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**Albedo** (`{{IPAc-en|æ|l|ˈ|b|iː|d|oʊ|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-albedo.wav}}`{=mediawiki} `{{respell|al|BEE|doh}}`{=mediawiki}; `{{etymology|la|albedo|whiteness}}`{=mediawiki}) is the fraction of sunlight that is diffusely reflected by a body. It is measured on a scale from 0 (corresponding to a black body that absorbs all incident radiation) to 1 (corresponding to a body that reflects all incident radiation). *Surface albedo* is defined as the ratio of radiosity *J*~e~ to the irradiance *E*~e~ (flux per unit area) received by a surface. The proportion reflected is not only determined by properties of the surface itself, but also by the spectral and angular distribution of solar radiation reaching the Earth\'s surface. These factors vary with atmospheric composition, geographic location, and time (see position of the Sun).
While directional-hemispherical reflectance factor is calculated for a single angle of incidence (i.e., for a given position of the Sun), albedo is the directional integration of reflectance over all solar angles in a given period. The temporal resolution may range from seconds (as obtained from flux measurements) to daily, monthly, or annual averages.
Unless given for a specific wavelength (spectral albedo), albedo refers to the entire spectrum of solar radiation. Due to measurement constraints, it is often given for the spectrum in which most solar energy reaches the surface (between 0.3 and 3 μm). This spectrum includes visible light (0.4--0.7 μm), which explains why surfaces with a low albedo appear dark (e.g., trees absorb most radiation), whereas surfaces with a high albedo appear bright (e.g., snow reflects most radiation).
Ice--albedo feedback is a positive feedback climate process where a change in the area of ice caps, glaciers, and sea ice alters the albedo and surface temperature of a planet. Ice is very reflective, therefore it reflects far more solar energy back to space than the other types of land area or open water. Ice--albedo feedback plays an important role in global climate change. Albedo is an important concept in climate science.
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## Terrestrial albedo {#terrestrial_albedo}
+------------------+---------------------+
| Surface | Typical\ |
| | albedo |
+==================+=====================+
| Fresh asphalt | 0.04{{cite web |
+------------------+---------------------+
| Open ocean | 0.06 |
+------------------+---------------------+
| Worn asphalt | 0.12 |
+------------------+---------------------+
| Conifer forest,\ | 0.08,{{Cite journal |
| summer | |
+------------------+---------------------+
| Deciduous forest | 0.15 to 0.18 |
+------------------+---------------------+
| Bare soil | 0.17{{Cite book |
+------------------+---------------------+
| Green grass | 0.25 |
+------------------+---------------------+
| Desert sand | 0.40{{Cite book |
+------------------+---------------------+
| New concrete | 0.55 |
+------------------+---------------------+
| Ocean ice | 0.50 to 0.70 |
+------------------+---------------------+
| Fresh snow | 0.80 |
+------------------+---------------------+
| Aluminium | 0.85 |
+------------------+---------------------+
: Sample albedos
Any albedo in visible light falls within a range of about 0.9 for fresh snow to about 0.04 for charcoal, one of the darkest substances. Deeply shadowed cavities can achieve an effective albedo approaching the zero of a black body. When seen from a distance, the ocean surface has a low albedo, as do most forests, whereas desert areas have some of the highest albedos among landforms. Most land areas are in an albedo range of 0.1 to 0.4. The average albedo of Earth is about 0.3. This is far higher than for the ocean primarily because of the contribution of clouds.
Earth\'s surface albedo is regularly estimated via Earth observation satellite sensors such as NASA\'s MODIS instruments on board the Terra and Aqua satellites, and the CERES instrument on the Suomi NPP and JPSS. As the amount of reflected radiation is only measured for a single direction by satellite, not all directions, a mathematical model is used to translate a sample set of satellite reflectance measurements into estimates of directional-hemispherical reflectance and bi-hemispherical reflectance (e.g.,). These calculations are based on the bidirectional reflectance distribution function (BRDF), which describes how the reflectance of a given surface depends on the view angle of the observer and the solar angle. BDRF can facilitate translations of observations of reflectance into albedo.
Earth\'s average surface temperature due to its albedo and the greenhouse effect is currently about 15 C. If Earth were frozen entirely (and hence be more reflective), the average temperature of the planet would drop below −40 C. If only the continental land masses became covered by glaciers, the mean temperature of the planet would drop to about 0 C. In contrast, if the entire Earth was covered by water -- a so-called ocean planet -- the average temperature on the planet would rise to almost 27 C.
In 2021, scientists reported that Earth dimmed by \~0.5% over two decades (1998--2017) as measured by earthshine using modern photometric techniques. This may have both been co-caused by climate change as well as a substantial increase in global warming. However, the link to climate change has not been explored to date and it is unclear whether or not this represents an ongoing trend.
### White-sky, black-sky, and blue-sky albedo {#white_sky_black_sky_and_blue_sky_albedo}
For land surfaces, it has been shown that the albedo at a particular solar zenith angle *θ*~*i*~ can be approximated by the proportionate sum of two terms:
- the directional-hemispherical reflectance at that solar zenith angle, ${\bar \alpha(\theta_i)}$, sometimes referred to as black-sky albedo, and
- the bi-hemispherical reflectance, $\bar{ \bar \alpha}$, sometimes referred to as white-sky albedo.
with ${1-D}$ being the proportion of direct radiation from a given solar angle, and ${D}$ being the proportion of diffuse illumination, the actual albedo ${\alpha}$ (also called blue-sky albedo) can then be given as:
$$\alpha = (1 - D) \bar\alpha(\theta_i) + D \bar{\bar\alpha}.$$
This formula is important because it allows the albedo to be calculated for any given illumination conditions from a knowledge of the intrinsic properties of the surface.
### Changes to albedo due to human activities {#changes_to_albedo_due_to_human_activities}
Human activities (e.g., deforestation, farming, and urbanization) change the albedo of various areas around the globe. Human impacts to \"the physical properties of the land surface can perturb the climate by altering the Earth's radiative energy balance\" even on a small scale or when undetected by satellites.
Urbanization generally decreases albedo (commonly being 0.01--0.02 lower than adjacent croplands), which contributes to global warming. Deliberately increasing albedo in urban areas can mitigate the urban heat island effect. An estimate in 2022 found that on a global scale, \"an albedo increase of 0.1 in worldwide urban areas would result in a cooling effect that is equivalent to absorbing \~44 Gt of CO~2~ emissions.\"
Intentionally enhancing the albedo of the Earth\'s surface, along with its daytime thermal emittance, has been proposed as a solar radiation management strategy to mitigate energy crises and global warming known as passive daytime radiative cooling (PDRC). Efforts toward widespread implementation of PDRCs may focus on maximizing the albedo of surfaces from very low to high values, so long as a thermal emittance of at least 90% can be achieved.
The tens of thousands of hectares of greenhouses in Almería, Spain form a large expanse of whitened plastic roofs. A 2008 study found that this anthropogenic change lowered the local surface area temperature of the high-albedo area, although changes were localized. A follow-up study found that \"CO2-eq. emissions associated to changes in surface albedo are a consequence of land transformation\" and can reduce surface temperature increases associated with climate change.
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## Examples of terrestrial albedo effects {#examples_of_terrestrial_albedo_effects}
thumb\|upright=1.3\|The percentage of diffusely reflected sunlight relative to various surface conditions
### Illumination
Albedo is not directly dependent on the illumination because changing the amount of incoming light proportionally changes the amount of reflected light, except in circumstances where a change in illumination induces a change in the Earth\'s surface at that location (e.g. through melting of reflective ice). However, albedo and illumination both vary by latitude. Albedo is highest near the poles and lowest in the subtropics, with a local maximum in the tropics.
### Insolation effects {#insolation_effects}
The intensity of albedo temperature effects depends on the amount of albedo and the level of local insolation (solar irradiance); high albedo areas in the Arctic and Antarctic regions are cold due to low insolation, whereas areas such as the Sahara Desert, which also have a relatively high albedo, will be hotter due to high insolation. Tropical and sub-tropical rainforest areas have low albedo, and are much hotter than their temperate forest counterparts, which have lower insolation. Because insolation plays such a big role in the heating and cooling effects of albedo, high insolation areas like the tropics will tend to show a more pronounced fluctuation in local temperature when local albedo changes.
Arctic regions notably release more heat back into space than what they absorb, effectively cooling the Earth. This has been a concern since arctic ice and snow has been melting at higher rates due to higher temperatures, creating regions in the arctic that are notably darker (being water or ground which is darker color) and reflects less heat back into space. This feedback loop results in a reduced albedo effect.
### Climate and weather {#climate_and_weather}
thumb\|right\|upright=1.5\| Some effects of global warming can either enhance (positive feedbacks such as the ice-albedo feedback) or inhibit (negative feedbacks) warming. Albedo affects climate by determining how much radiation a planet absorbs. The uneven heating of Earth from albedo variations between land, ice, or ocean surfaces can drive weather.
The response of the climate system to an initial forcing is modified by feedbacks: increased by \"self-reinforcing\" or \"positive\" feedbacks and reduced by \"balancing\" or \"negative\" feedbacks. The main reinforcing feedbacks are the water-vapour feedback, the ice--albedo feedback, and the net effect of clouds.
### Albedo--temperature feedback {#albedotemperature_feedback}
When an area\'s albedo changes due to snowfall, a snow--temperature feedback results. A layer of snowfall increases local albedo, reflecting away sunlight, leading to local cooling. In principle, if no outside temperature change affects this area (e.g., a warm air mass), the raised albedo and lower temperature would maintain the current snow and invite further snowfall, deepening the snow--temperature feedback. However, because local weather is dynamic due to the change of seasons, eventually warm air masses and a more direct angle of sunlight (higher insolation) cause melting. When the melted area reveals surfaces with lower albedo, such as grass, soil, or ocean, the effect is reversed: the darkening surface lowers albedo, increasing local temperatures, which induces more melting and thus reducing the albedo further, resulting in still more heating.
### Snow
Snow albedo is highly variable, ranging from as high as 0.9 for freshly fallen snow, to about 0.4 for melting snow, and as low as 0.2 for dirty snow. Over Antarctica, snow albedo averages a little more than 0.8. If a marginally snow-covered area warms, snow tends to melt, lowering the albedo, and hence leading to more snowmelt because more radiation is being absorbed by the snowpack (referred to as the ice--albedo positive feedback).
In Switzerland, the citizens have been protecting their glaciers with large white tarpaulins to slow down the ice melt. These large white sheets are helping to reject the rays from the sun and defecting the heat. Although this method is very expensive, it has been shown to work, reducing snow and ice melt by 60%.
Just as fresh snow has a higher albedo than does dirty snow, the albedo of snow-covered sea ice is far higher than that of sea water. Sea water absorbs more solar radiation than would the same surface covered with reflective snow. When sea ice melts, either due to a rise in sea temperature or in response to increased solar radiation from above, the snow-covered surface is reduced, and more surface of sea water is exposed, so the rate of energy absorption increases. The extra absorbed energy heats the sea water, which in turn increases the rate at which sea ice melts. As with the preceding example of snowmelt, the process of melting of sea ice is thus another example of a positive feedback. Both positive feedback loops have long been recognized as important for global warming.
Cryoconite, powdery windblown dust containing soot, sometimes reduces albedo on glaciers and ice sheets.
The dynamical nature of albedo in response to positive feedback, together with the effects of small errors in the measurement of albedo, can lead to large errors in energy estimates. Because of this, in order to reduce the error of energy estimates, it is important to measure the albedo of snow-covered areas through remote sensing techniques rather than applying a single value for albedo over broad regions.
### Small-scale effects {#small_scale_effects}
Albedo works on a smaller scale, too. In sunlight, dark clothes absorb more heat and light-coloured clothes reflect it better, thus allowing some control over body temperature by exploiting the albedo effect of the colour of external clothing.
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## Examples of terrestrial albedo effects {#examples_of_terrestrial_albedo_effects}
### Solar photovoltaic effects {#solar_photovoltaic_effects}
Albedo can affect the electrical energy output of solar photovoltaic devices. For example, the effects of a spectrally responsive albedo are illustrated by the differences between the spectrally weighted albedo of solar photovoltaic technology based on hydrogenated amorphous silicon (a-Si:H) and crystalline silicon (c-Si)-based compared to traditional spectral-integrated albedo predictions. Research showed impacts of over 10% for vertically (90°) mounted systems, but such effects were substantially lower for systems with lower surface tilts. Spectral albedo strongly affects the performance of bifacial solar cells where rear surface performance gains of over 20% have been observed for c-Si cells installed above healthy vegetation. An analysis on the bias due to the specular reflectivity of 22 commonly occurring surface materials (both human-made and natural) provided effective albedo values for simulating the performance of seven photovoltaic materials mounted on three common photovoltaic system topologies: industrial (solar farms), commercial flat rooftops and residential pitched-roof applications.
### Trees
Forests generally have a low albedo because the majority of the ultraviolet and visible spectrum is absorbed through photosynthesis. For this reason, the greater heat absorption by trees could offset some of the carbon benefits of afforestation (or offset the negative climate impacts of deforestation). In other words: The climate change mitigation effect of carbon sequestration by forests is partially counterbalanced in that reforestation can decrease the reflection of sunlight (albedo).
In the case of evergreen forests with seasonal snow cover, albedo reduction may be significant enough for deforestation to cause a net cooling effect. Trees also impact climate in extremely complicated ways through evapotranspiration. The water vapor causes cooling on the land surface, causes heating where it condenses, acts as strong greenhouse gas, and can increase albedo when it condenses into clouds. Scientists generally treat evapotranspiration as a net cooling impact, and the net climate impact of albedo and evapotranspiration changes from deforestation depends greatly on local climate.
Mid-to-high-latitude forests have a much lower albedo during snow seasons than flat ground, thus contributing to warming. Modeling that compares the effects of albedo differences between forests and grasslands suggests that expanding the land area of forests in temperate zones offers only a temporary mitigation benefit.
In seasonally snow-covered zones, winter albedos of treeless areas are 10% to 50% higher than nearby forested areas because snow does not cover the trees as readily. Deciduous trees have an albedo value of about 0.15 to 0.18 whereas coniferous trees have a value of about 0.09 to 0.15. Variation in summer albedo across both forest types is associated with maximum rates of photosynthesis because plants with high growth capacity display a greater fraction of their foliage for direct interception of incoming radiation in the upper canopy. The result is that wavelengths of light not used in photosynthesis are more likely to be reflected back to space rather than being absorbed by other surfaces lower in the canopy.
Studies by the Hadley Centre have investigated the relative (generally warming) effect of albedo change and (cooling) effect of carbon sequestration on planting forests. They found that new forests in tropical and midlatitude areas tended to cool; new forests in high latitudes (e.g., Siberia) were neutral or perhaps warming.
Research in 2023, drawing from 176 flux stations globally, revealed a climate trade-off: increased carbon uptake from afforestation results in reduced albedo. Initially, this reduction may lead to moderate global warming over a span of approximately 20 years, but it is expected to transition into significant cooling thereafter.
### Water
thumb\|upright=1.3\|Reflectivity of smooth water at 20 C (refractive index=1.333) Water reflects light very differently from typical terrestrial materials. The reflectivity of a water surface is calculated using the Fresnel equations.
At the scale of the wavelength of light even wavy water is always smooth so the light is reflected in a locally specular manner (not diffusely). The glint of light off water is a commonplace effect of this. At small angles of incident light, waviness results in reduced reflectivity because of the steepness of the reflectivity-vs.-incident-angle curve and a locally increased average incident angle.
Although the reflectivity of water is very low at low and medium angles of incident light, it becomes very high at high angles of incident light such as those that occur on the illuminated side of Earth near the terminator (early morning, late afternoon, and near the poles). However, as mentioned above, waviness causes an appreciable reduction. Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light.
Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces which reflect, adding up their reflectivities. Fresh \'black\' ice exhibits Fresnel reflection. Snow on top of this sea ice increases the albedo to 0.9.
### Clouds
Cloud albedo has substantial influence over atmospheric temperatures. Different types of clouds exhibit different reflectivity, theoretically ranging in albedo from a minimum of near 0 to a maximum approaching 0.8. \"On any given day, about half of Earth is covered by clouds, which reflect more sunlight than land and water. Clouds keep Earth cool by reflecting sunlight, but they can also serve as blankets to trap warmth.\"
Albedo and climate in some areas are affected by artificial clouds, such as those created by the contrails of heavy commercial airliner traffic. A study following the burning of the Kuwaiti oil fields during Iraqi occupation showed that temperatures under the burning oil fires were as much as 10 C-change colder than temperatures several miles away under clear skies.
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## Examples of terrestrial albedo effects {#examples_of_terrestrial_albedo_effects}
### Aerosol effects {#aerosol_effects}
Aerosols (very fine particles/droplets in the atmosphere) have both direct and indirect effects on Earth\'s radiative balance. The direct (albedo) effect is generally to cool the planet; the indirect effect (the particles act as cloud condensation nuclei and thereby change cloud properties) is less certain.
### Black carbon {#black_carbon}
Another albedo-related effect on the climate is from black carbon particles. The size of this effect is difficult to quantify: the Intergovernmental Panel on Climate Change estimates that the global mean radiative forcing for black carbon aerosols from fossil fuels is +0.2 W m^−2^, with a range +0.1 to +0.4 W m^−2^. Black carbon is a bigger cause of the melting of the polar ice cap in the Arctic than carbon dioxide due to its effect on the albedo.`{{Failed verification|date=January 2020}}`{=mediawiki}
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## Astronomical albedo {#astronomical_albedo}
thumb\|upright=1.2\|The moon Titan is darker than Saturn even though they receive the same amount of sunlight. This is due to a difference in albedo (0.22 versus 0.499 in geometric albedo).In astronomy, the term **albedo** can be defined in several different ways, depending upon the application and the wavelength of electromagnetic radiation involved.
### Optical or visual albedo {#optical_or_visual_albedo}
The albedos of planets, satellites and minor planets such as asteroids can be used to infer much about their properties. The study of albedos, their dependence on wavelength, lighting angle (\"phase angle\"), and variation in time composes a major part of the astronomical field of photometry. For small and far objects that cannot be resolved by telescopes, much of what we know comes from the study of their albedos. For example, the absolute albedo can indicate the surface ice content of outer Solar System objects, the variation of albedo with phase angle gives information about regolith properties, whereas unusually high radar albedo is indicative of high metal content in asteroids.
Enceladus, a moon of Saturn, has one of the highest known optical albedos of any body in the Solar System, with an albedo of 0.99. Another notable high-albedo body is Eris, with an albedo of 0.96. Many small objects in the outer Solar System and asteroid belt have low albedos down to about 0.05. A typical comet nucleus has an albedo of 0.04. Such a dark surface is thought to be indicative of a primitive and heavily space weathered surface containing some organic compounds.
The overall albedo of the Moon is measured to be around 0.14, but it is strongly directional and non-Lambertian, displaying also a strong opposition effect. Although such reflectance properties are different from those of any terrestrial terrains, they are typical of the regolith surfaces of airless Solar System bodies.
Two common optical albedos that are used in astronomy are the (V-band) geometric albedo (measuring brightness when illumination comes from directly behind the observer) and the Bond albedo (measuring total proportion of electromagnetic energy reflected). Their values can differ significantly, which is a common source of confusion.
Planet Geometric Bond
--------- ----------- ------------------------------------
Mercury 0.142 0.088 or 0.068
Venus 0.689 0.76 or 0.77
Earth 0.434 0.294
Mars 0.170 0.250
Jupiter 0.538 0.343±0.032 and also 0.503±0.012
Saturn 0.499 0.342
Uranus 0.488 0.300
Neptune 0.442 0.290
In detailed studies, the directional reflectance properties of astronomical bodies are often expressed in terms of the five Hapke parameters which semi-empirically describe the variation of albedo with phase angle, including a characterization of the opposition effect of regolith surfaces. One of these five parameters is yet another type of albedo called the single-scattering albedo. It is used to define scattering of electromagnetic waves on small particles. It depends on properties of the material (refractive index), the size of the particle, and the wavelength of the incoming radiation.
An important relationship between an object\'s astronomical (geometric) albedo, absolute magnitude and diameter is given by: $A =\left ( \frac{1329\times10^{-H/5}}{D} \right ) ^2,$ where $A$ is the astronomical albedo, $D$ is the diameter in kilometers, and $H$ is the absolute magnitude.
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## Astronomical albedo {#astronomical_albedo}
### Radar albedo {#radar_albedo}
In planetary radar astronomy, a microwave (or radar) pulse is transmitted toward a planetary target (e.g. Moon, asteroid, etc.) and the echo from the target is measured. In most instances, the transmitted pulse is circularly polarized and the received pulse is measured in the same sense of polarization as the transmitted pulse (SC) and the opposite sense (OC). The echo power is measured in terms of radar cross-section, ${\sigma}_{OC}$, ${\sigma}_{SC}$, or ${\sigma}_{T}$ (total power, SC + OC) and is equal to the cross-sectional area of a metallic sphere (perfect reflector) at the same distance as the target that would return the same echo power.
Those components of the received echo that return from first-surface reflections (as from a smooth or mirror-like surface) are dominated by the OC component as there is a reversal in polarization upon reflection. If the surface is rough at the wavelength scale or there is significant penetration into the regolith, there will be a significant SC component in the echo caused by multiple scattering.
For most objects in the solar system, the OC echo dominates and the most commonly reported radar albedo parameter is the (normalized) OC radar albedo (often shortened to radar albedo): $\hat{\sigma}_\text{OC} = \frac{{\sigma}_\text{OC}}{\pi r^2}$
where the denominator is the effective cross-sectional area of the target object with mean radius, $r$. A smooth metallic sphere would have $\hat{\sigma}_\text{OC} = 1$.
#### Radar albedos of Solar System objects {#radar_albedos_of_solar_system_objects}
Object $\hat{\sigma}_\text{OC}$
---------------------- --------------------------
Moon 0.06
Mercury 0.05
Venus 0.10
Mars 0.06
Avg. S-type asteroid 0.14
Avg. C-type asteroid 0.13
Avg. M-type asteroid 0.26
Comet P/2005 JQ5 0.02
The values reported for the Moon, Mercury, Mars, Venus, and Comet P/2005 JQ5 are derived from the total (OC+SC) radar albedo reported in those references.
#### Relationship to surface bulk density {#relationship_to_surface_bulk_density}
In the event that most of the echo is from first surface reflections ($\hat{\sigma}_\text{OC} < 0.1$ or so), the OC radar albedo is a first-order approximation of the Fresnel reflection coefficient (aka reflectivity) and can be used to estimate the bulk density of a planetary surface to a depth of a meter or so (a few wavelengths of the radar wavelength which is typically at the decimeter scale) using the following empirical relationships:
$$\rho = \begin{cases}
3.20 \text{ g cm}^{-3} \ln \left( \frac{1 + \sqrt{0.83 \hat{\sigma}_\text{OC}}}{1 - \sqrt{0.83 \hat{\sigma}_\text{OC}}} \right) & \text{for } \hat{\sigma}_\text{OC} \le 0.07 \\
(6.944 \hat{\sigma}_\text{OC} + 1.083) \text{ g cm}^{-3} & \text{for } \hat{\sigma}_\text{OC} > 0.07
\end{cases}$$.
## History
The term albedo was introduced into optics by Johann Heinrich Lambert in his 1760 work *Photometria*
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A-sharp}} `{{CS1 config|mode=}}`{=mediawiki} `{{Use dmy dates|date=November 2019}}`{=mediawiki} `{{Infobox grapheme
| letter = A a
| script = [[Latin script]]
| type = [[Alphabet]]
| typedesc = ic
| language = [[Latin language]]
| phonemes = {{flex list|width=2em|[{{IPAlink|a}}]|[{{IPAlink|ɑ}}]|[{{IPAlink|ɒ}}]|[{{IPAlink|æ}}]|[{{IPAlink|ə}}]|[{{IPAlink|ɛ}}]|[{{IPAlink|oː}}]|[{{IPAlink|ɔ}}]|[{{IPAlink|e}}]|[{{IPAlink|ʕ}}]|[{{IPAlink|ʌ}}] [{{IPAlink|ɐ}}] |{{IPAc-en|eɪ}}}}
| unicode = U+0041, U+0061
| alphanumber = 1
| fam1 = <hiero>F1</hiero>
| fam2 = [[File:Proto-semiticA-01.svg|class=skin-invert-image|20px|Proto-Sinaitic 'alp]]
| fam3 = [[File:Protoalef.svg|class=skin-invert-image|20px|Proto-Caananite aleph]]
| fam4 = [[File:Phoenician_aleph.svg|class=skin-invert-image|20px|Phoenician aleph]]
| fam5 = [[Alpha|Α α]]
| fam6 = [[𐌀]][[File:Greek-uncial-1.jpg|class=skin-invert-image|20px|Greek classical uncial]]
| fam7 = [[File:Semitic-2.jpg|class=skin-invert-image|20px|Early Latin A]][[File:Latin-uncial-1.jpg|class=skin-invert-image|20px|Latin 300 AD uncial, version 1]]
| usageperiod = {{circa|700 BCE}}{{snd}}present
| children = {{flex list|
* [[Æ]]
* [[Ä]]
* [[Â]]
* [[Ɑ]]
* [[Ʌ]]
* [[Ɐ]]
* [[ª]]
* [[Å]]
* [[₳]]
* [[@]]
* [[Ⓐ]]
* [[ⓐ]]
* [[⒜]]
* {{not a typo|[[🅰]]}}}}
| sisters = {{flex list|width=3em|
* [[𐌰]]
* [[А]]
* [[Ә]]
* [[Ӑ]]
* [[Aleph|<span>א</span> <span>ا</span> <span>ܐ</span>]]
* [[ࠀ]]
* [[𐎀]]
* [[ℵ]]
* [[አ]]
* [[ء]]
* [[Ա|Ա ա]]
* [[અ]]
* [[अ]]
* [[অ]]}}
| associates = [[List of Latin-script digraphs#A|a(x)]], [[Ae (digraph)|ae]], [[Eau (trigraph)|eau]], [[Au (digraph)|au]]
| direction = Left-to-right
| image = Latin_letter_A.svg
| imageclass = skin-invert-image
}}`{=mediawiki} `{{Latin letter info|a}}`{=mediawiki}
**A**, or **a**, is the first letter and the first vowel letter of the Latin alphabet, used in the modern English alphabet, and others worldwide. Its name in English is *a* (pronounced `{{IPAc-en|'|eɪ|audio=LL-Q1860 (eng)-Flame, not lame-A.wav}}`{=mediawiki} `{{respell|AY}}`{=mediawiki}), plural *aes*.`{{refn|group=nb|''Aes'' is the plural of the name of the letter. The plural of the letter itself is rendered ''A''s, A's, ''a''s, or a's.}}`{=mediawiki}
It is similar in shape to the Ancient Greek letter alpha, from which it derives. The uppercase version consists of the two slanting sides of a triangle, crossed in the middle by a horizontal bar. The lowercase version is often written in one of two forms: the double-storey \|a\| and single-storey \|ɑ\|. The latter is commonly used in handwriting and fonts based on it, especially fonts intended to be read by children, and is also found in italic type.
In English, *a* is the indefinite article, with the alternative form *an*.
## Name
In English, the name of the letter is the *long A* sound, pronounced `{{IPAc-en|'|eɪ}}`{=mediawiki}. Its name in most other languages matches the letter\'s pronunciation in open syllables. `{{wide image|Pronunciation of the name of the letter ⟨a⟩ in European languages.png|460px|Pronunciation of the name of the letter {{angbr|a}} in European languages. {{IPA|/a/}} and {{IPA|/aː/}} can differ phonetically between {{IPAblink|a}}, {{IPAblink|ä}}, {{IPAblink|æ}} and {{IPAblink|ɑ}} depending on the language.}}`{=mediawiki}
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## History
The earliest known ancestor of A is *aleph*---the first letter of the Phoenician alphabet---where it represented a glottal stop `{{IPA|[ʔ]}}`{=mediawiki}, as Phoenician only used consonantal letters. In turn, the ancestor of aleph may have been a pictogram of an ox head in proto-Sinaitic script influenced by Egyptian hieroglyphs, styled as a triangular head with two horns extended.
When the ancient Greeks adopted the alphabet, they had no use for a letter representing a glottal stop---so they adapted the sign to represent the vowel `{{IPAslink|a}}`{=mediawiki}, calling the letter by the similar name *alpha*. In the earliest Greek inscriptions dating to the 8th century BC following the Greek Dark Ages, the letter rests upon its side. However, in the later Greek alphabet it generally resembles the modern capital form---though many local varieties can be distinguished by the shortening of one leg, or by the angle at which the cross line is set.
The Etruscans brought the Greek alphabet to the Italian Peninsula, and left the form of alpha unchanged. When the Romans adopted the Etruscan alphabet to write Latin, the resulting form used in the Latin script would come to be used to write many other languages, including English.
Egyptian Proto-Sinaitic Proto-Canaanite Phoenician Western Greek Etruscan Latin
---------- ---------------- ----------------- ------------ --------------- ---------- -------
### Typographic variants {#typographic_variants}
class=skin-invert-image\|thumb\|upright=0.55\|Different glyphs of the lowercase letter `{{angbr|a}}`{=mediawiki} thumb\|upright=0.55\|Allographs include a double-storey `{{angbr|a}}`{=mediawiki} and single-storey `{{angbr|ɑ}}`{=mediawiki}. `{{stack end}}`{=mediawiki} During Roman times, there were many variant forms of the letter A. First was the monumental or lapidary style, which was used when inscribing on stone or other more permanent media. There was also a cursive style used for everyday or utilitarian writing, which was done on more perishable surfaces. Due to the perishable nature of these surfaces, there are not as many examples of this style as there are of the monumental, but there are still many surviving examples of different types of cursive, such as majuscule cursive, minuscule cursive, and semi-cursive minuscule. Variants also existed that were intermediate between the monumental and cursive styles. The known variants include the early semi-uncial (`{{cx|3rd century}}`{=mediawiki}), the uncial (`{{cx|4th–8th centuries}}`{=mediawiki}), and the late semi-uncial (`{{cx|6th–8th centuries}}`{=mediawiki}).
------------- ---------
Blackletter Uncial
Roman Italic
------------- ---------
At the end of the Roman Empire (5th century AD), several variants of the cursive minuscule developed through Western Europe. Among these were the semi-cursive minuscule of Italy, the Merovingian script in France, the Visigothic script in Spain, and the Insular or Anglo-Irish semi-uncial or Anglo-Saxon majuscule of Great Britain. By the ninth century, the Caroline script, which was very similar to the present-day form, was the principal form used in book-making, before the advent of the printing press. This form was derived through a combining of prior forms.
15th-century Italy saw the formation of the two main variants that are known today. These variants, the *Italic* and *Roman* forms, were derived from the Caroline Script version. The Italic form `{{angbr|ɑ}}`{=mediawiki}, also called *script a*, is often used in handwriting; it consists of a circle with a vertical stroke on its right. In the hands of medieval Irish and English writers, this form gradually developed from a 5th-century form resembling the Greek letter tau `{{angbr|τ}}`{=mediawiki}. The Roman form `{{angbr|a}}`{=mediawiki} is found in most printed material, and consists of a small loop with an arc over it. Both derive from the majuscule form `{{angbr|A}}`{=mediawiki}. In Greek handwriting, it was common to join the left leg and horizontal stroke into a single loop, as demonstrated by the uncial version shown. Many fonts then made the right leg vertical. In some of these, the serif that began the right leg stroke developed into an arc, resulting in the printed form, while in others it was dropped, resulting in the modern handwritten form. Graphic designers refer to the *Italic* and *Roman* forms as *single-decker a* and *double decker a* respectively.
Italic type is commonly used to mark emphasis or more generally to distinguish one part of a text from the rest set in Roman type. There are some other cases aside from italic type where *script a* `{{angbr|ɑ}}`{=mediawiki}, also called *Latin alpha*, is used in contrast with Latin `{{angbr|a}}`{=mediawiki}, such as in the International Phonetic Alphabet.
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## Use in writing systems {#use_in_writing_systems}
Orthography Phonemes
------------- -------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------
(pinyin)
English , `{{IPAslink|ɑː}}`{=mediawiki}, `{{IPAslink|ɒ}}`{=mediawiki}, `{{IPAslink|ɔː}}`{=mediawiki}, `{{IPA link|ɛ|/ɛː/}}`{=mediawiki}, `{{IPA|/eɪ/}}`{=mediawiki}, `{{IPAslink|ə}}`{=mediawiki}
French , `{{IPAslink|ɑ}}`{=mediawiki}
German , `{{IPAslink|aː}}`{=mediawiki}
Portuguese , `{{IPAslink|ɐ}}`{=mediawiki}
Saanich
Spanish
Turkish
: Pronunciation of `{{angbr|a}}`{=mediawiki} by language
Phone Orthography
------- -------------------------------------------------------------------------------------------------------------------------------------------------------------
Chuvash, Croatian, French, German, Indonesian, Italian, Malay, Polish, Portuguese, Spanish, Stavangersk Norwegian, Swedish, Tagalog, Turkish, Utrecht Dutch
Dutch (doubled), German
Afrikaans, Bulgarian, Spanish
New Zealand English, Lithuanian, Limburgish (doubled), Luxembourgish
Catalan, Czech, French, Northern England English, Terengganu Malay, Polish
West Frisian (doubled)
Bashkir, Spanish, Dutch, Finnish, French, Kaingang, Limburgish, Norwegian, Russian, West Frisian
Afrikaans (doubled), Danish, German, Southern England English, Kurdish, Norwegian
Azerbaijani, Kazakh, Luxembourgish
Southern England English, Hungarian, Kedah Malay
Hungarian
Swedish
Maastrichtian Limburgish, Ulster Irish
Danish, English, Russian, Zeta--Raška Serbian
Australian English, Bulgarian, Central Catalan, Emilian, Galician, Lithuanian, Portuguese, Tagalog, Ukrainian
Mapudungun
New Zealand English, Perak Malay
Chemnitz German, Transylvanian Romanian
Chemnitz German
Southern England English
English, Eastern Catalan
Saanich
English
: Cross-linguistic variation of `{{angbr|a}}`{=mediawiki} pronunciation
### English
In modern English orthography, the letter `{{angbr|a}}`{=mediawiki} represents at least seven different vowel sounds, here represented using the vowels of Received Pronunciation, with effects of `{{angbr|r}}`{=mediawiki} ignored and mergers in General American mentioned where relevant:
- the near-open front unrounded vowel `{{IPA|/æ/}}`{=mediawiki} as in *pad*
- the open back unrounded vowel `{{IPA|/ɑː/}}`{=mediawiki} as in *father*---merged with `{{IPAslink|ɒ}}`{=mediawiki} as `{{IPAslink|ɑ}}`{=mediawiki} in General American---which is closer to its original Latin and Greek sound
- the open back rounded vowel `{{IPA|/ɒ/}}`{=mediawiki} (merged with `{{IPA|/ɑː/}}`{=mediawiki} as `{{IPAslink|ɑ}}`{=mediawiki} in General American) in *was* and *what*
- the open-mid back rounded vowel `{{IPA|/ɔː/}}`{=mediawiki} in *water*
- the diphthong `{{IPA|/eɪ/}}`{=mediawiki} as in *ace* and *major*, usually when `{{vr|a}}`{=mediawiki} is followed by one, or occasionally two, consonants and then another vowel letter---this results from Middle English lengthening followed by the Great Vowel Shift
- a schwa `{{IPA|/ə/}}`{=mediawiki} in many unstressed syllables, as in *about*, *comma*, *solar*
The double `{{angbr|aa}}`{=mediawiki} sequence does not occur in native English words, but is found in some words derived from foreign languages such as *Aaron* and *aardvark*. However, `{{vr|a}}`{=mediawiki} occurs in many common digraphs, all with their own sound or sounds, particularly `{{vr|ai}}`{=mediawiki}, `{{vr|au}}`{=mediawiki}, `{{vr|aw}}`{=mediawiki}, `{{vr|ay}}`{=mediawiki}, `{{vr|ea}}`{=mediawiki} and `{{vr|oa}}`{=mediawiki}.
is the third-most-commonly used letter in English after `{{angbr|e}}`{=mediawiki} and `{{angbr|t}}`{=mediawiki}, as well as in French; it is the second most common in Spanish, and the most common in Portuguese. `{{angbr|a}}`{=mediawiki} represents approximately 8.2% of letters as used in English texts; the figure is around 7.6% in French 11.5% in Spanish, and 14.6% in Portuguese.
### Other languages {#other_languages}
In most languages that use the Latin alphabet, `{{angbr|a}}`{=mediawiki} denotes an open unrounded vowel, such as `{{IPAslink|a}}`{=mediawiki}, `{{IPAslink|ä}}`{=mediawiki}, or `{{IPAslink|ɑ}}`{=mediawiki}. An exception is Saanich, in which `{{angbr|a}}`{=mediawiki}---and the glyph `{{angbr|[[Á]]}}`{=mediawiki}---stands for a close-mid front unrounded vowel `{{IPA|/e/}}`{=mediawiki}.
### Other systems {#other_systems}
- In the International Phonetic Alphabet, `{{angbr IPA|a}}`{=mediawiki} is used for the open front unrounded vowel, `{{angbr IPA|ä}}`{=mediawiki} is used for the open central unrounded vowel, and `{{angbr IPA|ɑ}}`{=mediawiki} is used for the open back unrounded vowel.
- In X-SAMPA, `{{angbr|a}}`{=mediawiki} is used for the open front unrounded vowel and `{{angbr|A}}`{=mediawiki} is used for the open back unrounded vowel.
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## Other uses {#other_uses}
- When using base-16 notation, A or a is the conventional numeral corresponding to the number 10.
- In algebra, the letter *a* along with various other letters of the alphabet is often used to denote a variable, with various conventional meanings in different areas of mathematics. In 1637, René Descartes \"invented the convention of representing unknowns in equations by x, y, and z, and knowns by a, b, and c\", and this convention is still often followed, especially in elementary algebra.
- In geometry, capital Latin letters are used to denote objects including line segments, lines, and rays A capital A is also typically used as one of the letters to represent an angle in a triangle, the lowercase a representing the side opposite angle A.
- A is often used to denote something or someone of a better or more prestigious quality or status: A−, A or A+, the best grade that can be assigned by teachers for students\' schoolwork; \"A grade\" for clean restaurants; A-list celebrities, A1 at Lloyd\'s for shipping, etc. Such associations can have a motivating effect, as exposure to the letter A has been found to improve performance, when compared with other letters.
- A is used to denote size, as in a narrow size shoe, or a small cup size in a brassiere.
## Related characters {#related_characters}
### Latin alphabet {#latin_alphabet}
- `{{angbr|Æ æ}}`{=mediawiki}: a ligature of `{{angbr|AE}}`{=mediawiki} originally used in Latin
- with diacritics: Å å Ǻ ǻ Ḁ ḁ ẚ Ă ă Ặ ặ Ắ ắ Ằ ằ Ẳ ẳ Ẵ ẵ Ȃ ȃ Â â Ậ ậ Ấ ấ Ầ ầ Ẫ ẫ Ẩ ẩ Ả ả Ǎ ǎ Ⱥ ⱥ Ȧ ȧ Ǡ ǡ Ạ ạ Ä ä Ǟ ǟ À à Ȁ ȁ Á á Ā ā Ā̀ ā̀ Ã ã Ą ą Ą́ ą́ Ą̃ ą̃ A̲ a̲ ᶏ
- Phonetic alphabet symbols related to A---the International Phonetic Alphabet only uses lowercase, but uppercase forms are used in some other writing systems:
- : Latin alpha, represents an open back unrounded vowel in the IPA
- : Latin small alpha with a retroflex hook
- : Turned A, represents a near-open central vowel in the IPA
- : Turned V, represents an open-mid back unrounded vowel in IPA
- : Turned alpha or script A, represents an open back rounded vowel in the IPA
- : Modifier letter small turned alpha
- : Small capital A, an obsolete or non-standard symbol in the International Phonetic Alphabet used to represent various sounds (mainly open vowels)
- : Modifier letters are used in the Uralic Phonetic Alphabet (UPA), sometimes encoded with Unicode subscripts and superscripts
- : Subscript small a is used in Indo-European studies
- : Small letter a reversed-schwa is used in the Teuthonista phonetic transcription system
- : Glottal A, used in the transliteration of Ugaritic
### Derived signs, symbols and abbreviations {#derived_signs_symbols_and_abbreviations}
- : ordinal indicator
- : Ångström sign
- : turned capital letter A, used in predicate logic to specify universal quantification (\"for all\")
- : At sign
- : Argentine austral
- : anarchy symbol
### Ancestor and sibling letters {#ancestor_and_sibling_letters}
- : Phoenician aleph, from which the following symbols originally derive:
- : Greek letter alpha, from which the following letters derive:
- : Cyrillic letter A
- : Coptic letter alpha
- : Old Italic A, the ancestor of modern Latin A
- : Runic letter ansuz, which probably derives from old Italic A
- : Gothic letter aza
- : Armenian letter ayb
## Other representations {#other_representations}
### Computing
The Latin letters `{{angbr|A}}`{=mediawiki} and `{{angbr|a}}`{=mediawiki} have Unicode encodings `{{unichar|0041|Latin capital letter A}}`{=mediawiki} and `{{unichar|0061|Latin small letter a}}`{=mediawiki}. These are the same code points as those used in ASCII and ISO 8859. There are also precomposed character encodings for `{{angbr|A}}`{=mediawiki} and `{{angbr|a}}`{=mediawiki} with diacritics, for most of those listed above; the remainder are produced using combining diacritics.
Variant forms of the letter have unique code points for specialist use: the alphanumeric symbols set in mathematics and science, Latin alpha in linguistics, and halfwidth and fullwidth forms for legacy CJK font compatibility. The Cyrillic and Greek homoglyphs of the Latin `{{angbr|A}}`{=mediawiki} have separate encodings `{{unichar|0410|Cyrillic capital letter A|nlink=A (Cyrillic)}}`{=mediawiki} and `{{unichar|0391|Greek capital letter alpha|nlink=Alpha}}`{=mediawiki}
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***An American in Paris*** is a jazz-influenced symphonic poem (or tone poem) for orchestra by American composer George Gershwin first performed in 1928. It was inspired by the time that Gershwin had spent in Paris and evokes the sights and energy of the French capital during the **\[\[Années folles\]\]**.
Gershwin scored the piece for the standard instruments of the symphony orchestra plus celesta, saxophones, and automobile horns. He brought back four Parisian taxi horns for the New York premiere of the composition, which took place on December 13, 1928, in Carnegie Hall, with Walter Damrosch conducting the New York Philharmonic. It was Damrosch who had commissioned Gershwin to write his Concerto in F following the earlier success of *Rhapsody in Blue* (1924). He completed the orchestration on November 18, less than four weeks before the work\'s premiere. He collaborated on the original program notes with critic and composer Deems Taylor.
On January 1, 2025, *An American in Paris* entered the public domain.
## Background
Although the story is likely apocryphal, Gershwin is said to have been attracted by Maurice Ravel\'s unusual chords, and Gershwin went on his first trip to Paris in 1926 ready to study with Ravel. After his initial student audition with Ravel turned into a sharing of musical theories, Ravel said he could not teach him, saying, \"Why be a second-rate Ravel when you can be a first-rate Gershwin?\"
Gershwin strongly encouraged Ravel to come to the United States for a tour. To this end, upon his return to New York, Gershwin joined the efforts of Ravel\'s friend Robert Schmitz, a pianist Ravel had met during the war, to urge Ravel to tour the U.S. Schmitz was the head of Pro Musica, promoting Franco-American musical relations, and was able to offer Ravel a \$10,000 fee for the tour, an enticement Gershwin knew would be important to Ravel.
Gershwin greeted Ravel in New York in March 1928 during a party held for Ravel\'s birthday by Éva Gauthier. Ravel\'s tour reignited Gershwin\'s desire to return to Paris, which he and his brother Ira did after meeting Ravel. Ravel\'s high praise of Gershwin in an introductory letter to Nadia Boulanger caused Gershwin to seriously consider taking much more time to study abroad in Paris. Yet after he played for her, she told him she could not teach him. Boulanger gave Gershwin basically the same advice she gave all her accomplished master students: \"What could I give you that you haven\'t already got?\" This did not set Gershwin back, as his real intent abroad was to complete a new work based on Paris and perhaps a second rhapsody for piano and orchestra to follow his *Rhapsody in Blue*. Paris at this time hosted many expatriate writers, among them Ezra Pound, W. B. Yeats, Ernest Hemingway, F. Scott Fitzgerald and artist Pablo Picasso.
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## Composition
{{-}} Gershwin based *An American in Paris* on a melodic fragment called \"Very Parisienne\", written in 1926 on his first visit to Paris as a gift to his hosts, Robert and Mabel Schirmer. Gershwin called it \"a rhapsodic ballet\"; it is written freely and in a much more modern idiom than his prior works.
Gershwin explained in *Musical America*, \"My purpose here is to portray the impressions of an American visitor in Paris as he strolls about the city, listens to the various street noises, and absorbs the French atmosphere.\"
The piece is structured into five sections, which culminate in a loose A--B--A format. Gershwin\'s first A episode introduces the two main \"walking\" themes in the \"Allegretto grazioso\" and develops a third theme in the \"Subito con brio\". The style of this A section is written in the typical French style of composers Claude Debussy and Les Six. This A section featured duple meter, singsong rhythms, and diatonic melodies with the sounds of oboe, English horn, and taxi horns. It also includes a melody fragment of the song \"La Sorella\" by Charles Borel-Clerc (1879--1959) (published in 1905).
The B section\'s \"Andante ma con ritmo deciso\" introduces the American Blues and spasms of homesickness.
The \"Allegro\" that follows continues to express homesickness in a faster twelve-bar blues. In the B section, Gershwin uses common time, syncopated rhythms, and bluesy melodies with the sounds of trumpet, saxophone, and snare drum. \"Moderato con grazia\" is the last A section that returns to the themes set in A. After recapitulating the \"walking\" themes, Gershwin overlays the slow blues theme from section B in the final \"Grandioso\".
## Response
Gershwin did not particularly like Walter Damrosch\'s interpretation at the world premiere of *An American in Paris*. He stated that Damrosch\'s sluggish, dragging tempo caused him to walk out of the hall during a matinee performance of this work. The audience, according to Edward Cushing, responded with \"a demonstration of enthusiasm impressively genuine in contrast to the conventional applause which new music, good and bad, ordinarily arouses.\"
Critics believed that *An American in Paris* was better crafted than Gershwin\'s Concerto in F. *Evening Post* did not think it belonged in a program with classical composers César Franck, Richard Wagner, or Guillaume Lekeu on its premiere. Gershwin responded to the critics:
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## Instrumentation
*An American in Paris* was originally scored for 3 flutes (3rd doubling on piccolo), 2 oboes, English horn, 2 clarinets in B-flat, bass clarinet in B-flat, 2 bassoons, 4 horns in F, 3 trumpets in B-flat, 3 trombones, tuba, timpani, snare drum, bass drum, triangle, wood block, ratchet, cymbals, low and high tom-toms, xylophone, glockenspiel, celesta, 4 taxi horns labeled as A, B, C, and D with circles around them (but tuned as follows: A=Ab, B=Bb, C=D, and D=low A), alto saxophone, tenor saxophone, baritone saxophone (all doubling soprano and alto saxophones), and strings. Although most modern audiences have heard the taxi horns using the incorrect notes of A, B, C, and D, it had been Gershwin\'s intention to use the notes A`{{Music|flat}}`{=mediawiki}~4~, B`{{Music|flat}}`{=mediawiki}~4~, D~5~, and A~3~. It is likely that in labeling the taxi horns as A, B, C, and D with circles, he was referring to the four horns, and not the notes that they played. The correct tuning of the horns in sequence = D horn = low Ab, A horn = Ab an octave higher, B horn = Bb just above the Ab, and C horn = high D above the Bb.
A major revision of the work by composer and arranger F. Campbell-Watson simplified the instrumentation by reducing the saxophones to only three instruments: alto, tenor and baritone; the soprano and alto saxophone doublings were eliminated to avoid changing instruments. This became the standard performing edition until 2000, when Gershwin specialist Jack Gibbons made his own restoration of the original orchestration of *An American in Paris*, working directly from Gershwin\'s original manuscript, including the restoration of Gershwin\'s soprano saxophone parts removed in Campbell-Watson\'s revision. Gibbons\' restored orchestration of *An American in Paris* was performed at London\'s Queen Elizabeth Hall on July 9, 2000, by the City of Oxford Orchestra conducted by Levon Parikian.
William Daly arranged the score for piano solo; this was published by New World Music in 1929.
## Preservation status {#preservation_status}
On September 22, 2013, it was announced that a musicological critical edition of the full orchestral score would be eventually released. The Gershwin family, working in conjunction with the Library of Congress and the University of Michigan, were working to make scores available to the public that represent Gershwin\'s true intent. It was unknown whether the critical score would include the four minutes of material Gershwin later deleted from the work (such as the restatement of the blues theme after the faster 12 bar blues section), or if the score would document changes in the orchestration during Gershwin\'s composition process.
The score to *An American in Paris* was scheduled to be issued first in a series of scores to be released. The entire project was expected to take 30 to 40 years to complete, but *An American in Paris* was planned to be an early volume in the series.
Two urtext editions of the work were published by the German publisher B-Note Music in 2015. The changes made by Campbell-Watson were withdrawn in both editions. In the extended urtext, 120 bars of music were re-integrated. Conductor Walter Damrosch had cut them shortly before the first performance.
On September 9, 2017, The Cincinnati Symphony Orchestra gave the world premiere of the long-awaited critical edition of the piece prepared by Mark Clague, director of the Gershwin initiative at the University of Michigan. This performance was of the original 1928 orchestration.
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## Recordings
*An American in Paris* has been frequently recorded. The first recording was made for the Victor Talking Machine Company in 1929 with Nathaniel Shilkret conducting the Victor Symphony Orchestra, drawn from members of the Philadelphia Orchestra. Gershwin was on hand to \"supervise\" the recording; however, Shilkret was reported to be in charge and eventually asked the composer to leave the recording studio. Then, a little later, Shilkret discovered there was no one to play the brief celesta solo during the slow section, so he hastily asked Gershwin if he might play the solo; Gershwin said he could and so he briefly participated in the actual recording. This recording is believed to use the taxi horns in the way that Gershwin had intended using the notes A-flat, B-flat, a higher D, and a lower A.
The radio broadcast of the September 8, 1937, Hollywood Bowl George Gershwin Memorial Concert, in which *An American in Paris,* also conducted by Shilkret, was second on the program, was recorded and was released in 1998 in a two-CD set.
Arthur Fiedler and the Boston Pops Orchestra recorded the work for RCA Victor, including one of the first stereo recordings of the music.
In 1945, Arturo Toscanini conducting the NBC Symphony Orchestra recorded the piece for RCA Victor, one of the few commercial recordings Toscanini made of music by an American composer.
The Seattle Symphony also recorded a version in 1990 of Gershwin\'s original score, before numerous edits were made resulting in the score as we hear it today.
The blues section of *An American in Paris* has been recorded separately by a number of artists; Ralph Flanagan & His Orchestra released it as a single in 1951 which reached No. 15 on the *Billboard* chart. Harry James released a version of the blues section on his 1953 album *One Night Stand,* recorded live at the Aragon Ballroom in Chicago (Columbia GL 522 and CL 522).
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## Use in film {#use_in_film}
In 1951, Metro-Goldwyn-Mayer released the musical film *An American in Paris*, featuring Gene Kelly and Leslie Caron and directed by Vincente Minnelli. Winning the 1951 Best Picture Oscar and numerous other awards, the film featured many tunes of Gershwin and concluded with an extensive, elaborate dance sequence built around the symphonic poem *An American in Paris* (arranged for the film by Johnny Green), which at the time was the most expensive musical number ever filmed, costing \$500,000 `{{USDCY|500000|1951}}`{=mediawiki}
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***Actresses*** (Catalan: ***Actrius***) is a 1997 Catalan language Spanish drama film produced and directed by Ventura Pons and based on the award-winning stage play *E.R.* by Josep Maria Benet i Jornet. The film has no male actors, with all roles played by females. The film was produced in 1996.
## Synopsis
In order to prepare herself to play a role commemorating the life of legendary actress Empar Ribera, young actress (Mercè Pons) interviews three established actresses who had been the Ribera\'s pupils: the international diva Glòria Marc (Núria Espert), the television star Assumpta Roca (Rosa Maria Sardà), and dubbing director Maria Caminal (Anna Lizaran).
## Cast
- Núria Espert as Glòria Marc
- Rosa Maria Sardà as Assumpta Roca
- Anna Lizaran as Maria Caminal
- Mercè Pons as Estudiant
## Recognition
### Screenings
*Actrius* screened in 2001 at the Grauman\'s Egyptian Theatre in an American Cinematheque retrospective of the works of its director. The film had first screened at the same location in 1998. It was also shown at the 1997 Stockholm International Film Festival.
### Reception
In *Movie - Film - Review*, Christopher Tookey wrote that though the actresses were \"competent in roles that may have some reference to their own careers\", the film \"is visually unimaginative, never escapes its stage origins, and is almost totally lacking in revelation or surprising incident\". Noting that there were \"occasional, refreshing moments of intergenerational bitchiness\", they did not \"justify comparisons to *All About Eve*\", and were \"insufficiently different to deserve critical parallels with *Rashomon*\". He also wrote that *The Guardian* called the film a \"slow, stuffy chamber-piece\", and that *The Evening Standard* stated the film\'s \"best moments exhibit the bitchy tantrums seething beneath the threesome\'s composed veneers\". MRQE wrote \"This cinematic adaptation of a theatrical work is true to the original, but does not stray far from a theatrical rendering of the story
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***Animalia*** is an illustrated children\'s book by Graeme Base. It was originally published in 1986, followed by a tenth anniversary edition in 1996, and a 25th anniversary edition in 2012. Over four million copies have been sold worldwide. A special numbered and signed anniversary edition was also published in 1996, with an embossed gold jacket.
## Synopsis
*Animalia* is an alliterative alphabet book and contains twenty-six illustrations, one for each letter of the alphabet. Each illustration features an animal from the animal kingdom (A is for alligator and armadillo, B is for butterfly, C is for cat, etc.) along with a tongue-twister utilizing the letter of the page for many of the words. The illustrations contain many other objects beginning with that letter that the reader can try to identify (e.g. the \"D\" entry features, besides a pair of dragons, the dinosaur *Diplodocus* and the pelycosaur *Dimetrodon*; however, there are not necessarily \"a thousand things, or maybe more\", contrary to what the author states; for instance, the \"A\" entry features an alarm clock, as does the \"C\" entry; also, a tennis racket appears in the \"T\" entry as well as in the \"R\" entry). As an additional challenge, the author has hidden a picture of himself as a child in every picture.
## Related products {#related_products}
Julia MacRae Books published an *Animalia* colouring book in 2008. H. N. Abrams also published a wall calendar colouring book version for children the same year.
H. N. Abrams published *The Animalia Wall Frieze*, a fold-out over 26 feet in length, in which the author created new riddles for each letter.
The Great American Puzzle Factory created a 300-piece jigsaw puzzle based on the book\'s cover.
## Adaptations
A television series was also created, based on the book, which airs in Canada. The Australian Children\'s Television Foundation released a teaching resource DVD-ROM in 2011 to accompany the TV series with teaching aids for classroom use.
In 2010, The Base Factory and AppBooks released Animalia as an application for iPad and iPhone/iPod Touch.
## Awards
*Animalia* won the Young Australian\'s Best Book Award in 1987 for Best Picture Story Book.
The Children\'s Book Council of Australia designated *Animalia* a 1987 Picture Book of the Year: Honour Book.
Kid\'s Own Australian Literature Awards named *Animalia* the 1988 Picture Book Winner
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**International Atomic Time** (abbreviated **TAI**, from its French name ***temps atomique international***) is a high-precision atomic coordinate time standard based on the notional passage of proper time on Earth\'s geoid. TAI is a weighted average of the time kept by over 450 atomic clocks in over 80 national laboratories worldwide. It is a continuous scale of time, without leap seconds, and it is the principal realisation of Terrestrial Time (with a fixed offset of epoch). It is the basis for Coordinated Universal Time (UTC), which is used for civil timekeeping all over the Earth\'s surface and which has leap seconds.
UTC deviates from TAI by a number of whole seconds. `{{as of|2017|01|01}}`{=mediawiki}, immediately after the most recent leap second was put into effect, UTC has been exactly 37 seconds behind TAI. The 37 seconds result from the initial difference of 10 seconds at the start of 1972, plus 27 leap seconds in UTC since 1972. In 2022, the General Conference on Weights and Measures decided to abandon the leap second by or before 2035, at which point the difference between TAI and UTC will remain fixed.
TAI may be reported using traditional means of specifying days, carried over from non-uniform time standards based on the rotation of the Earth. Specifically, both Julian days and the Gregorian calendar are used. TAI in this form was synchronised with Universal Time at the beginning of 1958, and the two have drifted apart ever since, due primarily to the slowing rotation of the Earth.
## Operation
TAI is a weighted average of the time kept by over 450 atomic clocks in over 80 national laboratories worldwide. The majority of the clocks involved are caesium clocks; the International System of Units (SI) definition of the second is based on caesium. The clocks are compared using GPS signals and two-way satellite time and frequency transfer. Due to the signal averaging TAI is an order of magnitude more stable than its best constituent clock.
The participating institutions each broadcast, in real time, a frequency signal with timecodes, which is their estimate of TAI. Time codes are usually published in the form of UTC, which differs from TAI by a well-known integer number of seconds. These time scales are denoted in the form *UTC(NPL)* in the UTC form, where *NPL* here identifies the National Physical Laboratory, UK. The TAI form may be denoted *TAI(NPL)*. The latter is not to be confused with *TA(NPL)*, which denotes an independent atomic time scale, not synchronised to TAI or to anything else.
The clocks at different institutions are regularly compared against each other. The International Bureau of Weights and Measures (BIPM, France), combines these measurements to retrospectively calculate the weighted average that forms the most stable time scale possible. This combined time scale is published monthly in \"Circular T\", and is the canonical TAI. This time scale is expressed in the form of tables of differences UTC − UTC(*k*) (equal to TAI − TAI(*k*)) for each participating institution *k*. The same circular also gives tables of TAI − TA(*k*), for the various unsynchronised atomic time scales.
Errors in publication may be corrected by issuing a revision of the faulty Circular T or by errata in a subsequent Circular T. Aside from this, once published in Circular T, the TAI scale is not revised. In hindsight, it is possible to discover errors in TAI and to make better estimates of the true proper time scale. Since the published circulars are definitive, better estimates do not create another version of TAI; it is instead considered to be creating a better realisation of Terrestrial Time (TT).
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## History
Early atomic time scales consisted of quartz clocks with frequencies calibrated by a single atomic clock; the atomic clocks were not operated continuously. Atomic timekeeping services started experimentally in 1955, using the first caesium atomic clock at the National Physical Laboratory, UK (NPL). It was used as a basis for calibrating the quartz clocks at the Royal Greenwich Observatory and to establish a time scale, called Greenwich Atomic (GA). The United States Naval Observatory began the A.1 scale on 13 September 1956, using an Atomichron commercial atomic clock, followed by the NBS-A scale at the National Bureau of Standards, Boulder, Colorado on 9 October 1957.
The International Time Bureau (BIH) began a time scale, T~m~ or AM, in July 1955, using both local caesium clocks and comparisons to distant clocks using the phase of VLF radio signals. The BIH scale, A.1, and NBS-A were defined by an epoch at the beginning of 1958 The procedures used by the BIH evolved, and the name for the time scale changed: *A3* in 1964 and *TA(BIH)* in 1969.
The SI second was defined in terms of the caesium atom in 1967. From 1971 to 1975 the General Conference on Weights and Measures and the International Committee for Weights and Measures made a series of decisions that designated the BIPM time scale International Atomic Time (TAI).
In the 1970s, it became clear that the clocks participating in TAI were ticking at different rates due to gravitational time dilation, and the combined TAI scale, therefore, corresponded to an average of the altitudes of the various clocks. Starting from the Julian Date 2443144.5 (1 January 1977 00:00:00 TAI), corrections were applied to the output of all participating clocks, so that TAI would correspond to proper time at the geoid (mean sea level). Because the clocks were, on average, well above sea level, this meant that TAI slowed by about one part in a trillion. The former uncorrected time scale continues to be published under the name *EAL* (*Échelle Atomique Libre*, meaning *Free Atomic Scale*).
The instant that the gravitational correction started to be applied serves as the epoch for Barycentric Coordinate Time (TCB), Geocentric Coordinate Time (TCG), and Terrestrial Time (TT), which represent three fundamental time scales in the Solar System. All three of these time scales were defined to read JD 2443144.5003725 (1 January 1977 00:00:32.184) exactly at that instant. TAI was henceforth a realisation of TT, with the equation TT(TAI) = TAI + 32.184 s.
The continued existence of TAI was questioned in a 2007 letter from the BIPM to the ITU-R which stated, \"In the case of a redefinition of UTC without leap seconds, the CCTF would consider discussing the possibility of suppressing TAI, as it would remain parallel to the continuous UTC.\"
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## Relation to UTC {#relation_to_utc}
Contrary to TAI, UTC is a discontinuous time scale. It is occasionally adjusted by leap seconds. Between these adjustments, it is composed of segments that are mapped to atomic time by a constant offset. From its beginning in 1961 through December 1971, the adjustments were made regularly in fractional leap seconds so that UTC approximated UT2. Afterwards, these adjustments were made only in whole seconds to approximate UT1. This was a compromise arrangement in order to enable a publicly broadcast time scale. The less frequent whole-second adjustments meant that the time scale would be more stable and easier to synchronize internationally. The fact that it continues to approximate UT1 means that tasks such as navigation which require a source of Universal Time continue to be well served by the public broadcast of UTC
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**Alain Connes** (`{{IPA|fr|alɛ̃ kɔn|lang}}`{=mediawiki}; born 1 April 1947) is a French mathematician, known for his contributions to the study of operator algebras and noncommutative geometry. He was a professor at the *italic=no*, *italic=no*, Ohio State University and Vanderbilt University. He was awarded the Fields Medal in 1982.
## Career
Alain Connes attended high school at `{{Interlanguage link|Lycée Saint-Charles (Marseille)|lt=Lycée Saint-Charles|fr|Lycée Saint-Charles (Marseille)}}`{=mediawiki} in Marseille, and was then a student of the classes préparatoires in `{{Interlanguage link|Lycée Thiers|lt=Lycée Thiers|fr}}`{=mediawiki}. Between 1966 and 1970 he studied at École normale supérieure in Paris, and in 1973 he obtained a PhD from Pierre and Marie Curie University, under the supervision of Jacques Dixmier.
From 1970 to 1974 he was research fellow at the French National Centre for Scientific Research and during 1975 he held a visiting position at Queen\'s University at Kingston in Canada.
In 1976 he returned to France and worked as professor at Pierre and Marie Curie University until 1980 and at CNRS between 1981 and 1984. Moreover, since 1979 he holds the Léon Motchane Chair at IHES. From 1984 until his retirement in 2017 he held the chair of Analysis and Geometry at Collège de France.
In parallel, he was awarded a distinguished professorship at Vanderbilt University between 2003 and 2012, and at Ohio State University between 2012 and 2021.
## Research
Connes\' main research interests revolved around operator algebras. Besides noncommutative geometry, he has applied his works in various areas of mathematics and number theory, differential geometry. Since the 1990s, he developed noncommutative geometry.
In his early work on von Neumann algebras in the 1970s, he succeeded in obtaining the almost complete classification of injective factors. He also formulated the Connes embedding problem.
Following this, he made contributions in operator K-theory and index theory, which culminated in the Baum--Connes conjecture. He also introduced cyclic cohomology in the early 1980s as a first step in the study of noncommutative differential geometry.
He was a member of Nicolas Bourbaki. Over many years, he collaborated extensively with Henri Moscovici.
## Awards and honours {#awards_and_honours}
Connes was awarded the Peccot-Vimont Prize in 1976, the Ampère Prize in 1980, the Fields Medal in 1982, the Clay Research Award in 2000 and the Crafoord Prize in 2001. The French National Centre for Scientific Research granted him the silver medal in 1977 and the gold medal in 2004.
He was an invited speaker at the International Congress of Mathematicians in 1974 at Vancouver and in 1986 at Berkeley, and a plenary speaker at the ICM in 1978 at Helsinki. He was awarded honorary degrees from Queen\'s University at Kingston in 1979, University of Rome Tor Vergata in 1997, University of Oslo in 1999, University of Southern Denmark in 2009, Université libre de Bruxelles in 2010 and Shanghai Fudan University in 2017.
Since 1982 he is a member of the French Academy of Sciences. He was elected member of several foreign academies and societies, including the Royal Danish Academy of Sciences and Letters in 1980, the Norwegian Academy of Science and Letters in 1983, the American Academy of Arts and Sciences in 1989, the London Mathematical Society in 1994, the Canadian Academy of Sciences in 1995 (incorporated since 2002 in the Royal Society of Canada), the US National Academy of Sciences in 1997, the Russian Academy of Science in 2003 and the Royal Academy of Science, Letters and Fine Arts of Belgium in 2016.
In 2001 he received (together with his co-authors André Lichnerowicz and Marco Schutzenberger) the Peano Prize for his work *Triangle of Thoughts.*
## Family
Alain Connes is the middle-born of three sons -- born to parents both of whom lived to be 101 years old. He married in 1971.
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## Books
- Alain Connes and Matilde Marcolli, *Noncommutative Geometry, Quantum Fields and Motives*, Colloquium Publications, American Mathematical Society, 2007, `{{ISBN|978-0-8218-4210-2}}`{=mediawiki} [1](http://www.alainconnes.org/docs/bookwebfinal.pdf)
- Alain Connes, André Lichnerowicz, and Marcel-Paul Schutzenberger, *Triangle of Thought*, translated by Jennifer Gage, American Mathematical Society, 2001, `{{ISBN|978-0-8218-2614-0}}`{=mediawiki}
- Jean-Pierre Changeux and Alain Connes, *Conversations on Mind, Matter, and Mathematics*, translated by M. B
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**Analysis of variance (ANOVA)** is a family of statistical methods used to compare the means of two or more groups by analyzing variance. Specifically, ANOVA compares the amount of variation *between* the group means to the amount of variation *within* each group. If the between-group variation is substantially larger than the within-group variation, it suggests that the group means are likely different. This comparison is done using an F-test. The underlying principle of ANOVA is based on the law of total variance, which states that the total variance in a dataset can be broken down into components attributable to different sources. In the case of ANOVA, these sources are the variation between groups and the variation within groups.
ANOVA was developed by the statistician Ronald Fisher. In its simplest form, it provides a statistical test of whether two or more population means are equal, and therefore generalizes the *t*-test beyond two means. `{{TOC limit}}`{=mediawiki}
## History
While the analysis of variance reached fruition in the 20th century, antecedents extend centuries into the past according to Stigler. These include hypothesis testing, the partitioning of sums of squares, experimental techniques and the additive model. Laplace was performing hypothesis testing in the 1770s. Around 1800, Laplace and Gauss developed the least-squares method for combining observations, which improved upon methods then used in astronomy and geodesy. It also initiated much study of the contributions to sums of squares. Laplace knew how to estimate a variance from a residual (rather than a total) sum of squares. By 1827, Laplace was using least squares methods to address ANOVA problems regarding measurements of atmospheric tides. Before 1800, astronomers had isolated observational errors resulting from reaction times (the \"personal equation\") and had developed methods of reducing the errors. The experimental methods used in the study of the personal equation were later accepted by the emerging field of psychology which developed strong (full factorial) experimental methods to which randomization and blinding were soon added. An eloquent non-mathematical explanation of the additive effects model was available in 1885.
Ronald Fisher introduced the term variance and proposed its formal analysis in a 1918 article on theoretical population genetics, *The Correlation Between Relatives on the Supposition of Mendelian Inheritance*. His first application of the analysis of variance to data analysis was published in 1921, *Studies in Crop Variation I*. This divided the variation of a time series into components representing annual causes and slow deterioration. Fisher\'s next piece, *Studies in Crop Variation II*, written with Winifred Mackenzie and published in 1923, studied the variation in yield across plots sown with different varieties and subjected to different fertiliser treatments. Analysis of variance became widely known after being included in Fisher\'s 1925 book *Statistical Methods for Research Workers*.
Randomization models were developed by several researchers. The first was published in Polish by Jerzy Neyman in 1923.
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## Example
The analysis of variance can be used to describe otherwise complex relations among variables. A dog show provides an example. A dog show is not a random sampling of the breed: it is typically limited to dogs that are adult, pure-bred, and exemplary. A histogram of dog weights from a show is likely to be rather complicated, like the yellow-orange distribution shown in the illustrations. Suppose we wanted to predict the weight of a dog based on a certain set of characteristics of each dog. One way to do that is to *explain* the distribution of weights by dividing the dog population into groups based on those characteristics. A successful grouping will split dogs such that (a) each group has a low variance of dog weights (meaning the group is relatively homogeneous) and (b) the mean of each group is distinct (if two groups have the same mean, then it isn\'t reasonable to conclude that the groups are, in fact, separate in any meaningful way). In the illustrations to the right, groups are identified as *X*~1~, *X*~2~, etc. In the first illustration, the dogs are divided according to the product (interaction) of two binary groupings: young vs old, and short-haired vs long-haired (e.g., group 1 is young, short-haired dogs, group 2 is young, long-haired dogs, etc.). Since the distributions of dog weight within each of the groups (shown in blue) has a relatively large variance, and since the means are very similar across groups, grouping dogs by these characteristics does not produce an effective way to explain the variation in dog weights: knowing which group a dog is in doesn\'t allow us to predict its weight much better than simply knowing the dog is in a dog show. Thus, this grouping fails to explain the variation in the overall distribution (yellow-orange).
An attempt to explain the weight distribution by grouping dogs as *pet vs working breed* and *less athletic vs more athletic* would probably be somewhat more successful (fair fit). The heaviest show dogs are likely to be big, strong, working breeds, while breeds kept as pets tend to be smaller and thus lighter. As shown by the second illustration, the distributions have variances that are considerably smaller than in the first case, and the means are more distinguishable. However, the significant overlap of distributions, for example, means that we cannot distinguish *X*~1~ and *X*~2~ reliably. Grouping dogs according to a coin flip might produce distributions that look similar.
An attempt to explain weight by breed is likely to produce a very good fit. All Chihuahuas are light and all St Bernards are heavy. The difference in weights between Setters and Pointers does not justify separate breeds. The analysis of variance provides the formal tools to justify these intuitive judgments. A common use of the method is the analysis of experimental data or the development of models. The method has some advantages over correlation: not all of the data must be numeric and one result of the method is a judgment in the confidence in an explanatory relationship.
## Classes of models {#classes_of_models}
There are three classes of models used in the analysis of variance, and these are outlined here.
### Fixed-effects models {#fixed_effects_models}
The fixed-effects model (class I) of analysis of variance applies to situations in which the experimenter applies one or more treatments to the subjects of the experiment to see whether the response variable values change. This allows the experimenter to estimate the ranges of response variable values that the treatment would generate in the population as a whole.
### Random-effects models {#random_effects_models}
Random-effects model (class II) is used when the treatments are not fixed. This occurs when the various factor levels are sampled from a larger population. Because the levels themselves are random variables, some assumptions and the method of contrasting the treatments (a multi-variable generalization of simple differences) differ from the fixed-effects model.
### Mixed-effects models {#mixed_effects_models}
A mixed-effects model (class III) contains experimental factors of both fixed and random-effects types, with appropriately different interpretations and analysis for the two types.
### Example {#example_1}
Teaching experiments could be performed by a college or university department to find a good introductory textbook, with each text considered a treatment. The fixed-effects model would compare a list of candidate texts. The random-effects model would determine whether important differences exist among a list of randomly selected texts. The mixed-effects model would compare the (fixed) incumbent texts to randomly selected alternatives.
Defining fixed and random effects has proven elusive, with multiple competing definitions.
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## Assumptions
The analysis of variance has been studied from several approaches, the most common of which uses a linear model that relates the response to the treatments and blocks. Note that the model is linear in parameters but may be nonlinear across factor levels. Interpretation is easy when data is balanced across factors but much deeper understanding is needed for unbalanced data.
### Textbook analysis using a normal distribution {#textbook_analysis_using_a_normal_distribution}
The analysis of variance can be presented in terms of a linear model, which makes the following assumptions about the probability distribution of the responses:
- Independence of observations -- this is an assumption of the model that simplifies the statistical analysis.
- Normality -- the distributions of the residuals are normal.
- Equality (or \"homogeneity\") of variances, called homoscedasticity---the variance of data in groups should be the same.
The separate assumptions of the textbook model imply that the errors are independently, identically, and normally distributed for fixed effects models, that is, that the errors ($\varepsilon$) are independent and $\varepsilon \thicksim N(0, \sigma^2).$
### Randomization-based analysis {#randomization_based_analysis}
In a randomized controlled experiment, the treatments are randomly assigned to experimental units, following the experimental protocol. This randomization is objective and declared before the experiment is carried out. The objective random-assignment is used to test the significance of the null hypothesis, following the ideas of C. S. Peirce and Ronald Fisher. This design-based analysis was discussed and developed by Francis J. Anscombe at Rothamsted Experimental Station and by Oscar Kempthorne at Iowa State University. Kempthorne and his students make an assumption of *unit treatment additivity*, which is discussed in the books of Kempthorne and David R. Cox.
#### Unit-treatment additivity {#unit_treatment_additivity}
In its simplest form, the assumption of unit-treatment additivity states that the observed response $y_{i,j}$ from experimental unit $i$ when receiving treatment $j$ can be written as the sum of the unit\'s response $y_i$ and the treatment-effect $t_j$, that is $y_{i,j}=y_i+t_j.$ The assumption of unit-treatment additivity implies that, for every treatment $j$, the $j$th treatment has exactly the same effect $t_j$ on every experiment unit.
The assumption of unit treatment additivity usually cannot be directly falsified, according to Cox and Kempthorne. However, many *consequences* of treatment-unit additivity can be falsified. For a randomized experiment, the assumption of unit-treatment additivity *implies* that the variance is constant for all treatments. Therefore, by contraposition, a necessary condition for unit-treatment additivity is that the variance is constant.
The use of unit treatment additivity and randomization is similar to the design-based inference that is standard in finite-population survey sampling.
#### Derived linear model {#derived_linear_model}
Kempthorne uses the randomization-distribution and the assumption of *unit treatment additivity* to produce a *derived linear model*, very similar to the textbook model discussed previously. The test statistics of this derived linear model are closely approximated by the test statistics of an appropriate normal linear model, according to approximation theorems and simulation studies. However, there are differences. For example, the randomization-based analysis results in a small but (strictly) negative correlation between the observations. In the randomization-based analysis, there is *no assumption* of a *normal* distribution and certainly *no assumption* of *independence*. On the contrary, *the observations are dependent*!
The randomization-based analysis has the disadvantage that its exposition involves tedious algebra and extensive time. Since the randomization-based analysis is complicated and is closely approximated by the approach using a normal linear model, most teachers emphasize the normal linear model approach. Few statisticians object to model-based analysis of balanced randomized experiments.
#### Statistical models for observational data {#statistical_models_for_observational_data}
However, when applied to data from non-randomized experiments or observational studies, model-based analysis lacks the warrant of randomization. For observational data, the derivation of confidence intervals must use *subjective* models, as emphasized by Ronald Fisher and his followers. In practice, the estimates of treatment-effects from observational studies generally are often inconsistent. In practice, \"statistical models\" and observational data are useful for suggesting hypotheses that should be treated very cautiously by the public.
### Summary of assumptions {#summary_of_assumptions}
The normal-model based ANOVA analysis assumes the independence, normality, and homogeneity of variances of the residuals. The randomization-based analysis assumes only the homogeneity of the variances of the residuals (as a consequence of unit-treatment additivity) and uses the randomization procedure of the experiment. Both these analyses require homoscedasticity, as an assumption for the normal-model analysis and as a consequence of randomization and additivity for the randomization-based analysis.
However, studies of processes that change variances rather than means (called dispersion effects) have been successfully conducted using ANOVA. There are *no* necessary assumptions for ANOVA in its full generality, but the *F*-test used for ANOVA hypothesis testing has assumptions and practical limitations which are of continuing interest.
Problems which do not satisfy the assumptions of ANOVA can often be transformed to satisfy the assumptions. The property of unit-treatment additivity is not invariant under a \"change of scale\", so statisticians often use transformations to achieve unit-treatment additivity. If the response variable is expected to follow a parametric family of probability distributions, then the statistician may specify (in the protocol for the experiment or observational study) that the responses be transformed to stabilize the variance. Also, a statistician may specify that logarithmic transforms be applied to the responses which are believed to follow a multiplicative model. According to Cauchy\'s functional equation theorem, the logarithm is the only continuous transformation that transforms real multiplication to addition.
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## Characteristics
ANOVA is used in the analysis of comparative experiments, those in which only the difference in outcomes is of interest. The statistical significance of the experiment is determined by a ratio of two variances. This ratio is independent of several possible alterations to the experimental observations: Adding a constant to all observations does not alter significance. Multiplying all observations by a constant does not alter significance. So ANOVA statistical significance result is independent of constant bias and scaling errors as well as the units used in expressing observations. In the era of mechanical calculation it was common to subtract a constant from all observations (when equivalent to dropping leading digits) to simplify data entry. This is an example of data coding.
## Algorithm
The calculations of ANOVA can be characterized as computing a number of means and variances, dividing two variances and comparing the ratio to a handbook value to determine statistical significance. Calculating a treatment effect is then trivial: \"the effect of any treatment is estimated by taking the difference between the mean of the observations which receive the treatment and the general mean\".
### Partitioning of the sum of squares {#partitioning_of_the_sum_of_squares}
`{{see also|Lack-of-fit sum of squares}}`{=mediawiki} ANOVA uses traditional standardized terminology. The definitional equation of sample variance is $s^2 = \frac{1}{n-1} \sum_i (y_i-\bar{y})^2$, where the divisor is called the degrees of freedom (DF), the summation is called the sum of squares (SS), the result is called the mean square (MS) and the squared terms are deviations from the sample mean. ANOVA estimates 3 sample variances: a total variance based on all the observation deviations from the grand mean, an error variance based on all the observation deviations from their appropriate treatment means, and a treatment variance. The treatment variance is based on the deviations of treatment means from the grand mean, the result being multiplied by the number of observations in each treatment to account for the difference between the variance of observations and the variance of means.
The fundamental technique is a partitioning of the total sum of squares *SS* into components related to the effects used in the model. For example, the model for a simplified ANOVA with one type of treatment at different levels.
$SS_\text{Total} = SS_\text{Error} + SS_\text{Treatments}$
The number of degrees of freedom *DF* can be partitioned in a similar way: one of these components (that for error) specifies a chi-squared distribution which describes the associated sum of squares, while the same is true for \"treatments\" if there is no treatment effect.
$DF_\text{Total} = DF_\text{Error} + DF_\text{Treatments}$
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## Algorithm
### The *F*-test {#the_f_test}
The *F*-test is used for comparing the factors of the total deviation. For example, in one-way, or single-factor ANOVA, statistical significance is tested for by comparing the F test statistic
$F = \frac{\text{variance between treatments}}{\text{variance within treatments}}$ $F = \frac{MS_\text{Treatments}}{MS_\text{Error}} = {{SS_\text{Treatments} / (I-1)} \over {SS_\text{Error} / (n_T-I)}}$
where *MS* is mean square, $I$ is the number of treatments and $n_T$ is the total number of cases to the *F*-distribution with $I - 1$ being the numerator degrees of freedom and $n_T - I$ the denominator degrees of freedom. Using the *F*-distribution is a natural candidate because the test statistic is the ratio of two scaled sums of squares each of which follows a scaled chi-squared distribution.
The expected value of F is $1 + {n \sigma^2_\text{Treatment}} / {\sigma^2_\text{Error}}$ (where $n$ is the treatment sample size) which is 1 for no treatment effect. As values of F increase above 1, the evidence is increasingly inconsistent with the null hypothesis. Two apparent experimental methods of increasing F are increasing the sample size and reducing the error variance by tight experimental controls.
There are two methods of concluding the ANOVA hypothesis test, both of which produce the same result:
- The textbook method is to compare the observed value of F with the critical value of F determined from tables. The critical value of F is a function of the degrees of freedom of the numerator and the denominator and the significance level (*α*). If F ≥ F~Critical~, the null hypothesis is rejected.
- The computer method calculates the probability (p-value) of a value of F greater than or equal to the observed value. The null hypothesis is rejected if this probability is less than or equal to the significance level (*α*).
The ANOVA *F*-test is known to be nearly optimal in the sense of minimizing false negative errors for a fixed rate of false positive errors (i.e. maximizing power for a fixed significance level). For example, to test the hypothesis that various medical treatments have exactly the same effect, the *F*-test\'s *p*-values closely approximate the permutation test\'s p-values: The approximation is particularly close when the design is balanced. Such permutation tests characterize tests with maximum power against all alternative hypotheses, as observed by Rosenbaum. The ANOVA *F*-test (of the null-hypothesis that all treatments have exactly the same effect) is recommended as a practical test, because of its robustness against many alternative distributions.
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## Algorithm
### Extended algorithm {#extended_algorithm}
ANOVA consists of separable parts; partitioning sources of variance and hypothesis testing can be used individually. ANOVA is used to support other statistical tools. Regression is first used to fit more complex models to data, then ANOVA is used to compare models with the objective of selecting simple(r) models that adequately describe the data. \"Such models could be fit without any reference to ANOVA, but ANOVA tools could then be used to make some sense of the fitted models, and to test hypotheses about batches of coefficients.\" \"\[W\]e think of the analysis of variance as a way of understanding and structuring multilevel models---not as an alternative to regression but as a tool for summarizing complex high-dimensional inferences \...\"
## For a single factor {#for_a_single_factor}
The simplest experiment suitable for ANOVA analysis is the completely randomized experiment with a single factor. More complex experiments with a single factor involve constraints on randomization and include completely randomized blocks and Latin squares (and variants: Graeco-Latin squares, etc.). The more complex experiments share many of the complexities of multiple factors.
There are some alternatives to conventional one-way analysis of variance, e.g.: Welch\'s heteroscedastic F test, Welch\'s heteroscedastic F test with trimmed means and Winsorized variances, Brown-Forsythe test, Alexander-Govern test, James second order test and Kruskal-Wallis test, available in [onewaytests](https://cran.r-project.org/web/packages/onewaytests/index.html) R
It is useful to represent each data point in the following form, called a statistical model: $Y_{ij} = \mu + \tau_j + \varepsilon_{ij}$ where
- *i* = 1, 2, 3, \..., *R*
- *j* = 1, 2, 3, \..., *C*
- *μ* = overall average (mean)
- *τ*~*j*~ = differential effect (response) associated with the *j* level of X; `{{pb}}`{=mediawiki} this assumes that overall the values of *τ*~*j*~ add to zero (that is, $\sum_{j = 1}^C \tau_j = 0$)
- *ε*~*ij*~ = noise or error associated with the particular *ij* data value
That is, we envision an additive model that says every data point can be represented by summing three quantities: the true mean, averaged over all factor levels being investigated, plus an incremental component associated with the particular column (factor level), plus a final component associated with everything else affecting that specific data value.
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## For multiple factors {#for_multiple_factors}
ANOVA generalizes to the study of the effects of multiple factors. When the experiment includes observations at all combinations of levels of each factor, it is termed factorial. Factorial experiments are more efficient than a series of single factor experiments and the efficiency grows as the number of factors increases. Consequently, factorial designs are heavily used.
The use of ANOVA to study the effects of multiple factors has a complication. In a 3-way ANOVA with factors x, y and z, the ANOVA model includes terms for the main effects (x, y, z) and terms for interactions (xy, xz, yz, xyz). All terms require hypothesis tests. The proliferation of interaction terms increases the risk that some hypothesis test will produce a false positive by chance. Fortunately, experience says that high order interactions are rare. `{{verify source|date=December 2014}}`{=mediawiki} The ability to detect interactions is a major advantage of multiple factor ANOVA. Testing one factor at a time hides interactions, but produces apparently inconsistent experimental results.
Caution is advised when encountering interactions; Test interaction terms first and expand the analysis beyond ANOVA if interactions are found. Texts vary in their recommendations regarding the continuation of the ANOVA procedure after encountering an interaction. Interactions complicate the interpretation of experimental data. Neither the calculations of significance nor the estimated treatment effects can be taken at face value. \"A significant interaction will often mask the significance of main effects.\" Graphical methods are recommended to enhance understanding. Regression is often useful. A lengthy discussion of interactions is available in Cox (1958). Some interactions can be removed (by transformations) while others cannot.
A variety of techniques are used with multiple factor ANOVA to reduce expense. One technique used in factorial designs is to minimize replication (possibly no replication with support of analytical trickery) and to combine groups when effects are found to be statistically (or practically) insignificant. An experiment with many insignificant factors may collapse into one with a few factors supported by many replications.
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## Associated analysis {#associated_analysis}
Some analysis is required in support of the *design* of the experiment while other analysis is performed after changes in the factors are formally found to produce statistically significant changes in the responses. Because experimentation is iterative, the results of one experiment alter plans for following experiments.
### Preparatory analysis {#preparatory_analysis}
#### The number of experimental units {#the_number_of_experimental_units}
In the design of an experiment, the number of experimental units is planned to satisfy the goals of the experiment. Experimentation is often sequential.
Early experiments are often designed to provide mean-unbiased estimates of treatment effects and of experimental error. Later experiments are often designed to test a hypothesis that a treatment effect has an important magnitude; in this case, the number of experimental units is chosen so that the experiment is within budget and has adequate power, among other goals.
Reporting sample size analysis is generally required in psychology. \"Provide information on sample size and the process that led to sample size decisions.\" The analysis, which is written in the experimental protocol before the experiment is conducted, is examined in grant applications and administrative review boards.
Besides the power analysis, there are less formal methods for selecting the number of experimental units. These include graphical methods based on limiting the probability of false negative errors, graphical methods based on an expected variation increase (above the residuals) and methods based on achieving a desired confidence interval.
#### Power analysis {#power_analysis}
Power analysis is often applied in the context of ANOVA in order to assess the probability of successfully rejecting the null hypothesis if we assume a certain ANOVA design, effect size in the population, sample size and significance level. Power analysis can assist in study design by determining what sample size would be required in order to have a reasonable chance of rejecting the null hypothesis when the alternative hypothesis is true.
#### Effect size {#effect_size}
Several standardized measures of effect have been proposed for ANOVA to summarize the strength of the association between a predictor(s) and the dependent variable or the overall standardized difference of the complete model. Standardized effect-size estimates facilitate comparison of findings across studies and disciplines. However, while standardized effect sizes are commonly used in much of the professional literature, a non-standardized measure of effect size that has immediately \"meaningful\" units may be preferable for reporting purposes.
#### Model confirmation {#model_confirmation}
Sometimes tests are conducted to determine whether the assumptions of ANOVA appear to be violated. Residuals are examined or analyzed to confirm homoscedasticity and gross normality. Residuals should have the appearance of (zero mean normal distribution) noise when plotted as a function of anything including time and modeled data values. Trends hint at interactions among factors or among observations.
#### Follow-up tests {#follow_up_tests}
A statistically significant effect in ANOVA is often followed by additional tests. This can be done in order to assess which groups are different from which other groups or to test various other focused hypotheses. Follow-up tests are often distinguished in terms of whether they are \"planned\" (a priori) or \"post hoc.\" Planned tests are determined before looking at the data, and post hoc tests are conceived only after looking at the data (though the term \"post hoc\" is inconsistently used).
The follow-up tests may be \"simple\" pairwise comparisons of individual group means or may be \"compound\" comparisons (e.g., comparing the mean pooling across groups A, B and C to the mean of group D). Comparisons can also look at tests of trend, such as linear and quadratic relationships, when the independent variable involves ordered levels. Often the follow-up tests incorporate a method of adjusting for the multiple comparisons problem.
Follow-up tests to identify which specific groups, variables, or factors have statistically different means include the Tukey\'s range test, and Duncan\'s new multiple range test. In turn, these tests are often followed with a Compact Letter Display (CLD) methodology in order to render the output of the mentioned tests more transparent to a non-statistician audience.
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## Study designs {#study_designs}
There are several types of ANOVA. Many statisticians base ANOVA on the design of the experiment, especially on the protocol that specifies the random assignment of treatments to subjects; the protocol\'s description of the assignment mechanism should include a specification of the structure of the treatments and of any blocking. It is also common to apply ANOVA to observational data using an appropriate statistical model.
Some popular designs use the following types of ANOVA:
- One-way ANOVA is used to test for differences among two or more independent groups (means), e.g. different levels of urea application in a crop, or different levels of antibiotic action on several different bacterial species, or different levels of effect of some medicine on groups of patients. However, should these groups not be independent, and there is an order in the groups (such as mild, moderate and severe disease), or in the dose of a drug (such as 5 mg/mL, 10 mg/mL, 20 mg/mL) given to the same group of patients, then a linear trend estimation should be used. Typically, however, the one-way ANOVA is used to test for differences among at least three groups, since the two-group case can be covered by a t-test. When there are only two means to compare, the t-test and the ANOVA *F*-test are equivalent; the relation between ANOVA and *t* is given by `{{math|1=''F'' = ''t''<sup>2</sup>}}`{=mediawiki}.
- Factorial ANOVA is used when there is more than one factor.
- Repeated measures ANOVA is used when the same subjects are used for each factor (e.g., in a longitudinal study).
- Multivariate analysis of variance (MANOVA) is used when there is more than one response variable.
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## Cautions
Balanced experiments (those with an equal sample size for each treatment) are relatively easy to interpret; unbalanced experiments offer more complexity. For single-factor (one-way) ANOVA, the adjustment for unbalanced data is easy, but the unbalanced analysis lacks both robustness and power. For more complex designs the lack of balance leads to further complications. \"The orthogonality property of main effects and interactions present in balanced data does not carry over to the unbalanced case. This means that the usual analysis of variance techniques do not apply. Consequently, the analysis of unbalanced factorials is much more difficult than that for balanced designs.\" In the general case, \"The analysis of variance can also be applied to unbalanced data, but then the sums of squares, mean squares, and *F*-ratios will depend on the order in which the sources of variation are considered.\"
ANOVA is (in part) a test of statistical significance. The American Psychological Association (and many other organisations) holds the view that simply reporting statistical significance is insufficient and that reporting confidence bounds is preferred.
## Generalizations
ANOVA is considered to be a special case of linear regression which in turn is a special case of the general linear model. All consider the observations to be the sum of a model (fit) and a residual (error) to be minimized.
The Kruskal-Wallis test and the Friedman test are nonparametric tests which do not rely on an assumption of normality.
### Connection to linear regression {#connection_to_linear_regression}
Below we make clear the connection between multi-way ANOVA and linear regression.
Linearly re-order the data so that $k$-th observation is associated with a response $y_k$ and factors $Z_{k,b}$ where $b \in \{1,2,\ldots,B\}$ denotes the different factors and $B$ is the total number of factors. In one-way ANOVA $B=1$ and in two-way ANOVA $B = 2$. Furthermore, we assume the $b$-th factor has $I_b$ levels, namely $\{1,2,\ldots,I_b\}$. Now, we can one-hot encode the factors into the $\sum_{b=1}^B I_b$ dimensional vector $v_k$.
The one-hot encoding function $g_b : \{1,2,\ldots,I_b\} \mapsto \{0,1\}^{I_b}$ is defined such that the $i$-th entry of $g_b(Z_{k,b})$ is $g_b(Z_{k,b})_i = \begin{cases}
1 & \text{if } i=Z_{k,b} \\
0 & \text{otherwise}
\end{cases}$ The vector $v_k$ is the concatenation of all of the above vectors for all $b$. Thus, $v_k = [g_1(Z_{k,1}), g_2(Z_{k,2}), \ldots, g_B(Z_{k,B})]$. In order to obtain a fully general $B$-way interaction ANOVA we must also concatenate every additional interaction term in the vector $v_k$ and then add an intercept term. Let that vector be $X_k$.
With this notation in place, we now have the exact connection with linear regression. We simply regress response $y_k$ against the vector $X_k$. However, there is a concern about identifiability. In order to overcome such issues we assume that the sum of the parameters within each set of interactions is equal to zero. From here, one can use *F*-statistics or other methods to determine the relevance of the individual factors.
#### Example {#example_2}
We can consider the 2-way interaction example where we assume that the first factor has 2 levels and the second factor has 3 levels.
Define $a_i = 1$ if $Z_{k,1}=i$ and $b_i = 1$ if $Z_{k,2} = i$, i.e. $a$ is the one-hot encoding of the first factor and $b$ is the one-hot encoding of the second factor.
With that, $X_k = [a_1, a_2, b_1, b_2, b_3 ,a_1 \times b_1, a_1 \times b_2, a_1 \times b_3, a_2 \times b_1, a_2 \times b_2, a_2 \times b_3, 1]$ where the last term is an intercept term
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**United States appellate procedure** involves the rules and regulations for filing appeals in state courts and federal courts. The nature of an appeal can vary greatly depending on the type of case and the rules of the court in the jurisdiction where the case was prosecuted. There are many types of standard of review for appeals, such as *de novo* and abuse of discretion. However, most appeals begin when a party files a petition for review to a higher court for the purpose of overturning the lower court\'s decision.
An appellate court is a court that hears cases on appeal from another court. Depending on the particular legal rules that apply to each circumstance, a party to a court case who is unhappy with the result might be able to challenge that result in an appellate court on specific grounds. These grounds typically could include errors of law, fact, procedure or due process. In different jurisdictions, appellate courts are also called appeals courts, courts of appeals, superior courts, or supreme courts.
The specific procedures for appealing, including even whether there is a right of appeal from a particular type of decision, can vary greatly from state to state. The right to file an appeal can also vary from state to state; for example, the New Jersey Constitution vests judicial power in a Supreme Court, a Superior Court, and other courts of limited jurisdiction, with an appellate court being part of the Superior Court.
## Access to appellant status {#access_to_appellant_status}
A party who files an appeal is called an \"appellant\", \"plaintiff in error\", \"petitioner\" or \"pursuer\", and a party on the other side is called an \"appellee\", \"defendant in error\", \"respondent\". A \"cross-appeal\" is an appeal brought by the respondent. For example, suppose at trial the judge found for the plaintiff and ordered the defendant to pay \$50,000. If the defendant files an appeal arguing that he should not have to pay any money, then the plaintiff might file a cross-appeal arguing that the defendant should have to pay \$200,000 instead of \$50,000.
The appellant is the party who, having lost part or all their claim in a lower court decision, is appealing to a higher court to have their case reconsidered. This is usually done on the basis that the lower court judge erred in the application of law, but it may also be possible to appeal on the basis of court misconduct, or that a finding of fact was entirely unreasonable to make on the evidence.
The appellant in the new case can be either the plaintiff (or claimant), defendant, third-party intervenor, or respondent (appellee) from the lower case, depending on who was the losing party. The winning party from the lower court, however, is now the respondent. In unusual cases the appellant can be the victor in the court below, but still appeal.
An appellee is the party to an appeal in which the lower court judgment was in its favor. The appellee is required to respond to the petition, oral arguments, and legal briefs of the appellant. In general, the appellee takes the procedural posture that the lower court\'s decision should be affirmed.
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## Ability to appeal {#ability_to_appeal}
An appeal \"as of right\" is one that is guaranteed by statute or some underlying constitutional or legal principle. The appellate court cannot refuse to listen to the appeal. An appeal \"by leave\" or \"permission\" requires the appellant to obtain leave to appeal; in such a situation either or both of the lower court and the court may have the discretion to grant or refuse the appellant\'s demand to appeal the lower court\'s decision. In the Supreme Court, review in most cases is available only if the Court exercises its discretion and grants a writ of certiorari.
In tort, equity, or other civil matters either party to a previous case may file an appeal. In criminal matters, however, the state or prosecution generally has no appeal \"as of right\". And due to the double jeopardy principle, the state or prosecution may never appeal a jury or bench verdict of acquittal. But in some jurisdictions, the state or prosecution may appeal \"as of right\" from a trial court\'s dismissal of an indictment in whole or in part or from a trial court\'s granting of a defendant\'s suppression motion. Likewise, in some jurisdictions, the state or prosecution may appeal an issue of law \"by leave\" from the trial court or the appellate court. The ability of the prosecution to appeal a decision in favor of a defendant varies significantly internationally. All parties must present grounds to appeal, or it will not be heard.
By convention in some law reports, the appellant is named first. This can mean that where it is the defendant who appeals, the name of the case in the law reports reverses (in some cases twice) as the appeals work their way up the court hierarchy. This is not always true, however. In the federal courts, the parties\' names always stay in the same order as the lower court when an appeal is taken to the circuit courts of appeals, and are re-ordered only if the appeal reaches the Supreme Court.
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## Direct or collateral: Appealing criminal convictions {#direct_or_collateral_appealing_criminal_convictions}
Many jurisdictions recognize two types of appeals, particularly in the criminal context. The first is the traditional \"direct\" appeal in which the appellant files an appeal with the next higher court of review. The second is the collateral appeal or post-conviction petition, in which the petitioner-appellant files the appeal in a court of first instance---usually the court that tried the case.
The key distinguishing factor between direct and collateral appeals is that the former occurs in state courts, and the latter in federal courts.`{{dubious|Non-federal collateral review|date=May 2017}}`{=mediawiki}
Relief in post-conviction is rare and is most often found in capital or violent felony cases. The typical scenario involves an incarcerated defendant locating DNA evidence demonstrating the defendant\'s actual innocence.
### Appellate review {#appellate_review}
\"Appellate review\" is the general term for the process by which courts with appellate jurisdiction take jurisdiction of matters decided by lower courts. It is distinguished from judicial review, which refers to the court\'s overriding constitutional or statutory right to determine if a legislative act or administrative decision is defective for jurisdictional or other reasons (which may vary by jurisdiction).
In most jurisdictions the normal and preferred way of seeking appellate review is by filing an appeal of the final judgment. Generally, an appeal of the judgment will also allow appeal of all other orders or rulings made by the trial court in the course of the case. This is because such orders cannot be appealed \"as of right\". However, certain critical interlocutory court orders, such as the denial of a request for an interim injunction, or an order holding a person in contempt of court, can be appealed immediately although the case may otherwise not have been fully disposed of.
There are two distinct forms of appellate review, \"direct\" and \"collateral\". For example, a criminal defendant may be convicted in state court, and lose on \"direct appeal\" to higher state appellate courts, and if unsuccessful, mount a \"collateral\" action such as filing for a writ of habeas corpus in the federal courts. Generally speaking, \"\[d\]irect appeal statutes afford defendants the opportunity to challenge the merits of a judgment and allege errors of law or fact. \... \[Collateral review\], on the other hand, provide\[s\] an independent and civil inquiry into the validity of a conviction and sentence, and as such are generally limited to challenges to constitutional, jurisdictional, or other fundamental violations that occurred at trial.\" \"Graham v. Borgen\", 483 F 3d. 475 (7th Cir. 2007) (no. 04--4103) (slip op. at 7) (citation omitted).
In Anglo-American common law courts, appellate review of lower court decisions may also be obtained by filing a petition for review by prerogative writ in certain cases. There is no corresponding right to a writ in any pure or continental civil law legal systems, though some mixed systems such as Quebec recognize these prerogative writs.
#### Direct appeal {#direct_appeal}
After exhausting the first appeal as of right, defendants usually petition the highest state court to review the decision. This appeal is known as a direct appeal. The highest state court, generally known as the Supreme Court, exercises discretion over whether it will review the case. On direct appeal, a prisoner challenges the grounds of the conviction based on an error that occurred at trial or some other stage in the adjudicative process.
##### Preservation issues {#preservation_issues}
An appellant\'s claim(s) must usually be preserved at trial. This means that the defendant had to object to the error when it occurred in the trial. Because constitutional claims are of great magnitude, appellate courts might be more lenient to review the claim even if it was not preserved. For example, Connecticut applies the following standard to review unpreserved claims: 1.the record is adequate to review the alleged claim of error; 2. the claim is of constitutional magnitude alleging the violation of a fundamental right; 3. the alleged constitutional violation clearly exists and clearly deprived the defendant of a fair trial; 4. if subject to harmless error analysis, the state has failed to demonstrate harmlessness of the alleged constitutional violation beyond a reasonable doubt.
#### State post-conviction relief: collateral appeal {#state_post_conviction_relief_collateral_appeal}
All States have a post-conviction relief process. Similar to federal post-conviction relief, an appellant can petition the court to correct alleged fundamental errors that were not corrected on direct review. Typical claims might include ineffective assistance of counsel and actual innocence based on new evidence. These proceedings are normally separate from the direct appeal, however some states allow for collateral relief to be sought on direct appeal. After direct appeal, the conviction is considered final. An appeal from the post conviction court proceeds just as a direct appeal. That is, it goes to the intermediate appellate court, followed by the highest court. If the petition is granted the appellant could be released from incarceration, the sentence could be modified, or a new trial could be ordered.
#### Habeas corpus {#habeas_corpus}
## Notice of appeal {#notice_of_appeal}
A \"notice of appeal\" is a form or document that in many cases is required to begin an appeal. The form is completed by the appellant or by the appellant\'s legal representative. The nature of this form can vary greatly from country to country and from court to court within a country.
The specific rules of the legal system will dictate exactly how the appeal is officially begun. For example, the appellant might have to file the notice of appeal with the appellate court, or with the court from which the appeal is taken, or both.
Some courts have samples of a notice of appeal on the court\'s own web site. In New Jersey, for example, the Administrative Office of the Court has promulgated a form of notice of appeal for use by appellants, though using this exact form is not mandatory and the failure to use it is not a jurisdictional defect provided that all pertinent information is set forth in whatever form of notice of appeal is used.
The deadline for beginning an appeal can often be very short: traditionally, it is measured in days, not months. This can vary from country to country, as well as within a country, depending on the specific rules in force. In the U.S. federal court system, criminal defendants must file a notice of appeal within 10 days of the entry of either the judgment or the order being appealed, or the right to appeal is forfeited.
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## Appellate procedure {#appellate_procedure}
Generally speaking the appellate court examines the record of evidence presented in the trial court and the law that the lower court applied and decides whether that decision was legally sound or not. The appellate court will typically be deferential to the lower court\'s findings of fact (such as whether a defendant committed a particular act), unless clearly erroneous, and so will focus on the court\'s application of the law to those facts (such as whether the act found by the court to have occurred fits a legal definition at issue).
If the appellate court finds no defect, it \"affirms\" the judgment. If the appellate court does find a legal defect in the decision \"below\" (i.e., in the lower court), it may \"modify\" the ruling to correct the defect, or it may nullify (\"reverse\" or \"vacate\") the whole decision or any part of it. It may, in addition, send the case back (\"remand\" or \"remit\") to the lower court for further proceedings to remedy the defect.
In some cases, an appellate court may review a lower court decision \"de novo\" (or completely), challenging even the lower court\'s findings of fact. This might be the proper standard of review, for example, if the lower court resolved the case by granting a pre-trial motion to dismiss or motion for summary judgment which is usually based only upon written submissions to the trial court and not on any trial testimony.
Another situation is where appeal is by way of \"re-hearing\". Certain jurisdictions permit certain appeals to cause the trial to be heard afresh in the appellate court.
Sometimes, the appellate court finds a defect in the procedure the parties used in filing the appeal and dismisses the appeal without considering its merits, which has the same effect as affirming the judgment below. (This would happen, for example, if the appellant waited too long, under the appellate court\'s rules, to file the appeal.)
Generally, there is no trial in an appellate court, only consideration of the record of the evidence presented to the trial court and all the pre-trial and trial court proceedings are reviewed---unless the appeal is by way of re-hearing, new evidence will usually only be considered on appeal in \"very\" rare instances, for example if that material evidence was unavailable to a party for some very significant reason such as prosecutorial misconduct.
In some systems, an appellate court will only consider the written decision of the lower court, together with any written evidence that was before that court and is relevant to the appeal. In other systems, the appellate court will normally consider the record of the lower court. In those cases the record will first be certified by the lower court.
The appellant has the opportunity to present arguments for the granting of the appeal and the appellee (or respondent) can present arguments against it. Arguments of the parties to the appeal are presented through their appellate lawyers, if represented, or \"pro se\" if the party has not engaged legal representation. Those arguments are presented in written briefs and sometimes in oral argument to the court at a hearing. At such hearings each party is allowed a brief presentation at which the appellate judges ask questions based on their review of the record below and the submitted briefs.
In an adversarial system, appellate courts do not have the power to review lower court decisions unless a party appeals it. Therefore, if a lower court has ruled in an improper manner, or against legal precedent, that judgment will stand if not appealed -- even if it might have been overturned on appeal.
The United States legal system generally recognizes two types of appeals: a trial \"de novo\" or an appeal on the record.
A trial de novo is usually available for review of informal proceedings conducted by some minor judicial tribunals in proceedings that do not provide all the procedural attributes of a formal judicial trial. If unchallenged, these decisions have the power to settle more minor legal disputes once and for all. If a party is dissatisfied with the finding of such a tribunal, one generally has the power to request a trial \"de novo\" by a court of record. In such a proceeding, all issues and evidence may be developed newly, as though never heard before, and one is not restricted to the evidence heard in the lower proceeding. Sometimes, however, the decision of the lower proceeding is itself admissible as evidence, thus helping to curb frivolous appeals.
In some cases, an application for \"trial de novo\" effectively erases the prior trial as if it had never taken place. The Supreme Court of Virginia has stated that \'\"This Court has repeatedly held that the effect of an appeal to circuit court is to \"annul the judgment of the inferior tribunal as completely as if there had been no previous trial.\"\' The only exception to this is that if a defendant appeals a conviction for a crime having multiple levels of offenses, where they are convicted on a lesser offense, the appeal is of the lesser offense; the conviction represents an acquittal of the more serious offenses. \"\[A\] trial on the same charges in the circuit court does not violate double jeopardy principles, . . . subject only to the limitation that conviction in \[the\] district court for an offense lesser included in the one charged constitutes an acquittal of the greater offense, permitting trial de novo in the circuit court only for the lesser-included offense.\"
In an appeal on the record from a decision in a judicial proceeding, both appellant and respondent are bound to base their arguments wholly on the proceedings and body of evidence as they were presented in the lower tribunal. Each seeks to prove to the higher court that the result they desired was the just result. Precedent and case law figure prominently in the arguments. In order for the appeal to succeed, the appellant must prove that the lower court committed reversible error, that is, an impermissible action by the court acted to cause a result that was unjust, and which would not have resulted had the court acted properly. Some examples of reversible error would be erroneously instructing the jury on the law applicable to the case, permitting seriously improper argument by an attorney, admitting or excluding evidence improperly, acting outside the court\'s jurisdiction, injecting bias into the proceeding or appearing to do so, juror misconduct, etc. The failure to formally object at the time, to what one views as improper action in the lower court, may result in the affirmance of the lower court\'s judgment on the grounds that one did not \"preserve the issue for appeal\" by objecting.
In cases where a judge rather than a jury decided issues of fact, an appellate court will apply an \"abuse of discretion\" standard of review. Under this standard, the appellate court gives deference to the lower court\'s view of the evidence, and reverses its decision only if it were a clear abuse of discretion. This is usually defined as a decision outside the bounds of reasonableness. On the other hand, the appellate court normally gives less deference to a lower court\'s decision on issues of law, and may reverse if it finds that the lower court applied the wrong legal standard.
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## Appellate procedure {#appellate_procedure}
In some cases, an appellant may successfully argue that the law under which the lower decision was rendered was unconstitutional or otherwise invalid, or may convince the higher court to order a new trial on the basis that evidence earlier sought was concealed or only recently discovered. In the case of new evidence, there must be a high probability that its presence or absence would have made a material difference in the trial. Another issue suitable for appeal in criminal cases is effective assistance of counsel. If a defendant has been convicted and can prove that his lawyer did not adequately handle his case and that there is a reasonable probability that the result of the trial would have been different had the lawyer given competent representation, he is entitled to a new trial.
A lawyer traditionally starts an oral argument to any appellate court with the words \"May it please the court.\"
After an appeal is heard, the \"mandate\" is a formal notice of a decision by a court of appeal; this notice is transmitted to the trial court and, when filed by the clerk of the trial court, constitutes the final judgment on the case, unless the appeal court has directed further proceedings in the trial court. The mandate is distinguished from the appeal court\'s opinion, which sets out the legal reasoning for its decision. In some jurisdictions the mandate is known as the \"remittitur\".
## Results
The result of an appeal can be:
:\*Affirmed: Where the reviewing court basically agrees with the result of the lower courts\' ruling(s).
:\*Reversed: Where the reviewing court basically disagrees with the result of the lower courts\' ruling(s), and overturns their decision.
:\*Vacated: Where the reviewing court overturns the lower courts\' ruling(s) as invalid, without necessarily disagreeing with it/them, e.g. because the case was decided on the basis of a legal principle that no longer applies.
:\*Remanded: Where the reviewing court sends the case back to the lower court.
There can be multiple outcomes, so that the reviewing court can affirm some rulings, reverse others and remand the case all at the same time. Remand is not required where there is nothing left to do in the case. \"Generally speaking, an appellate court\'s judgment provides \'the final directive of the appeals courts as to the matter appealed, setting out with specificity the court\'s determination that the action appealed from should be affirmed, reversed, remanded or modified\'\".
Some reviewing courts who have discretionary review may send a case back without comment other than *review improvidently granted*. In other words, after looking at the case, they chose not to say anything. The result for the case of *review improvidently granted* is effectively the same as affirmed, but without that extra higher court stamp of approval
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In law, an **answer** was originally a solemn assertion in opposition to someone or something, and thus generally any counter-statement or defense, a reply to a question or response, or objection, or a correct solution of a problem.
In the common law, an **answer** is the first pleading by a defendant, usually filed and served upon the plaintiff within a certain strict time limit after a civil complaint or criminal information or indictment has been served upon the defendant. It may have been preceded by an *optional* \"pre-answer\" motion to dismiss or demurrer; if such a motion is unsuccessful, the defendant *must* file an answer to the complaint or risk an adverse default judgment.
In a criminal case, there is usually an arraignment or some other kind of appearance before the defendant comes to court. The pleading in the criminal case, which is entered on the record in open court, is usually either guilty or not guilty. Generally, speaking in private, civil cases there is no plea entered of guilt or innocence. There is only a judgment that grants money damages or some other kind of equitable remedy such as restitution or a permanent injunction. Criminal cases may lead to fines or other punishment, such as imprisonment.
The famous Latin *Responsa Prudentium* (\"answers of the learned ones\") were the accumulated views of many successive generations of Roman lawyers, a body of legal opinion which gradually became authoritative.
During debates of a contentious nature, deflection, colloquially known as \'changing the topic\', has been widely observed, and is often seen as a failure to answer a question
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ASA film speed\|other uses\|ANSI (disambiguation)}} `{{Distinguish|ASCII}}`{=mediawiki} `{{Update|date=July 2020}}`{=mediawiki} `{{Use mdy dates|date=June 2013}}`{=mediawiki} `{{Infobox organization
| name = American National Standards Institute
| image = ANSI logo.svg
| alt = The official logo of the American National Standards Institute
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| abbreviation = ANSI
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| formation = {{Start date and age|1918|10|19|paren=yes}}<ref>{{cite journal|date=October 19, 1918|title=Minutes|journal=American Engineering Standards Committee |page=1}}</ref>
| type = [[Nonprofit organization]]
| status = [[501(c)(3) organization|501(c)(3)]] private
| purpose = [[Standards organization|National standards]]
| headquarters = [[Washington, D.C.]], U.S.<br />{{Coordinates|38|54|14|N|77|02|35|W}}
| location =
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| membership = 125,000 companies and 3.5 million professionals<ref name="membership" />
| language = [[American English|English]]
| leader_title = President and [[Chief executive officer|CEO]]
| leader_name = Laurie E. Locascio, PhD
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The **American National Standards Institute** (**ANSI** `{{IPAc-en|ˈ|æ|n|s|i|audio=LL-Q1860 (eng)-Naomi Persephone Amethyst (NaomiAmethyst)-ANSI.wav}}`{=mediawiki} `{{respell|AN|see}}`{=mediawiki}) is a private nonprofit organization that oversees the development of voluntary consensus standards for products, services, processes, systems, and personnel in the United States.`{{ref RFC|4949}}`{=mediawiki} The organization also coordinates U.S. standards with international standards so that American products can be used worldwide.
ANSI accredits standards that are developed by representatives of other standards organizations, government agencies, consumer groups, companies, and others. These standards ensure that the characteristics and performance of products are consistent, that people use the same definitions and terms, and that products are tested the same way. ANSI also accredits organizations that carry out product or personnel certification in accordance with requirements defined in international standards.
The organization\'s headquarters are in Washington, D.C. ANSI\'s operations office is located in New York City. The ANSI annual operating budget is funded by the sale of publications, membership dues and fees, accreditation services, fee-based programs, and international standards programs.
Many ANSI regulations are incorporated by reference into United States federal statutes (i.e. by OSHA regulations referring to individual ANSI specifications). ANSI does not make these standards publicly available, and charges money for access to these documents; it further claims that it is copyright infringement for them to be provided to the public by others free of charge. These assertions have been the subject of criticism and litigation.
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## History
ANSI was most likely formed in 1918, when five engineering societies and three government agencies founded the **American Engineering Standards Committee** (**AESC**). In 1928, the AESC became the **American Standards Association** (**ASA**).
In 1966, the ASA was reorganized and became the **United States of America Standards Institute** (**USASI**).
In February 1969, Ralph Nader harshly criticized the USASI in public remarks as \"manifestly deceptive\" in several different ways. He specifically attacked the name USASI as improperly implying some kind of official connection with the federal government of the United States.
The present name was adopted in 1969.
Prior to 1918, these five founding engineering societies:
- American Institute of Electrical Engineers (AIEE, now IEEE)
- American Society of Mechanical Engineers (ASME)
- American Society of Civil Engineers (ASCE)
- American Institute of Mining Engineers (AIME, now American Institute of Mining, Metallurgical, and Petroleum Engineers)
- American Society for Testing and Materials (now ASTM International)
had been members of the United Engineering Society (UES). At the behest of the AIEE, they invited the U.S. government Departments of War, Navy (combined in 1947 to become the Department of Defense or DOD) and Commerce to join in founding a national standards organization.
According to Adam Stanton, the first permanent secretary and head of staff in 1919, AESC started as an ambitious program and little else. Staff for the first year consisted of one executive, Clifford B. LePage, who was on loan from a founding member, ASME. An annual budget of \$7,500 was provided by the founding bodies.
In 1931, the organization (renamed ASA in 1928) became affiliated with the U.S. National Committee of the International Electrotechnical Commission (IEC), which had been formed in 1904 to develop electrical and electronics standards.
## Members
ANSI\'s members are government agencies, organizations, academic and international bodies, and individuals. In total, the Institute represents the interests of more than 270,000 companies and organizations and 30 million professionals worldwide.
ANSI\'s market-driven, decentralized approach has been criticized in comparison with more planned and organized international approaches to standardization. An underlying issue is the difficulty of balancing \"the interests of both the nation\'s industrial and commercial sectors and the nation as a whole.\"
## Process
Although ANSI itself does not develop standards, the Institute oversees the development and use of standards by accrediting the procedures of standards developing organizations. ANSI accreditation signifies that the procedures used by standards developing organizations meet the institute\'s requirements for openness, balance, consensus, and due process.
ANSI also designates specific standards as American National Standards, or ANS, when the Institute determines that the standards were developed in an environment that is equitable, accessible and responsive to the requirements of various stakeholders.
Voluntary consensus standards quicken the market acceptance of products while making clear how to improve the safety of those products for the protection of consumers. There are approximately 9,500 American National Standards that carry the ANSI designation.
The American National Standards process involves:
- consensus by a group that is open to representatives from all interested parties
- broad-based public review and comment on draft standards
- consideration of and response to comments
- incorporation of submitted changes that meet the same consensus requirements into a draft standard
- availability of an appeal by any participant alleging that these principles were not respected during the standards-development process.
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## International activities {#international_activities}
In addition to facilitating the formation of standards in the United States, ANSI promotes the use of U.S. standards internationally, advocates U.S. policy and technical positions in international and regional standards organizations, and encourages the adoption of international standards as national standards where appropriate.
The institute is the official U.S. representative to the two major international standards organizations, the International Organization for Standardization (ISO), as a founding member, and the International Electrotechnical Commission (IEC), via the U.S. National Committee (USNC). ANSI participates in almost the entire technical program of both the ISO and the IEC, and administers many key committees and subgroups. In many instances, U.S. standards are taken forward to ISO and IEC, through ANSI or the USNC, where they are adopted in whole or in part as international standards.
Adoption of ISO and IEC standards as American standards increased from 0.2% in 1986 to 15.5% in May 2012.
### Standards panels {#standards_panels}
The Institute administers nine standards panels:
- ANSI Homeland Defense and Security Standardization Collaborative (HDSSC)
- ANSI Nanotechnology Standards Panel (ANSI-NSP)
- ID Theft Prevention and ID Management Standards Panel (IDSP)
- ANSI Energy Efficiency Standardization Coordination Collaborative (EESCC)
- Nuclear Energy Standards Coordination Collaborative (NESCC)
- Electric Vehicles Standards Panel (EVSP)
- ANSI-NAM Network on Chemical Regulation
- ANSI Biofuels Standards Coordination Panel
- Healthcare Information Technology Standards Panel (HITSP)
Each of the panels works to identify, coordinate, and harmonize voluntary standards relevant to these areas.
In 2009, ANSI and the National Institute of Standards and Technology (NIST) formed the Nuclear Energy Standards Coordination Collaborative (NESCC). NESCC is a joint initiative to identify and respond to the current need for standards in the nuclear industry.
### American national standards {#american_national_standards}
- The ASA (as for American Standards Association) photographic exposure system, originally defined in ASA Z38.2.1 (since 1943) and ASA PH2.5 (since 1954), together with the DIN system (DIN 4512 since 1934), became the basis for the ISO system (since 1974), currently used worldwide (ISO 6, ISO 2240, ISO 5800, ISO 12232).
- A standard for the set of values used to represent characters in digital computers. The ANSI code standard extended the previously created ASCII seven bit code standard (ASA X3.4-1963), with additional codes for European alphabets (see also Extended Binary Coded Decimal Interchange Code or EBCDIC). In Microsoft Windows, the phrase \"ANSI\" refers to the Windows ANSI code pages (even though they are not ANSI standards). Most of these are fixed width, though some characters for ideographic languages are variable width. Since these characters are based on a draft of the ISO-8859 series, some of Microsoft\'s symbols are visually very similar to the ISO symbols, leading many to falsely assume that they are identical.
- The first computer programming language standard was \"American Standard Fortran\" (informally known as \"FORTRAN 66\"), approved in March 1966 and published as ASA X3.9-1966.
- The programming language COBOL had ANSI standards in 1968, 1974, and 1985. The COBOL 2002 standard was issued by ISO.
- The original standard implementation of the C programming language was standardized as ANSI X3.159-1989, becoming the well-known ANSI C.
- The X3J13 committee was created in 1986 to formalize the ongoing consolidation of Common Lisp, culminating in 1994 with the publication of ANSI\'s first object-oriented programming standard.
- A popular Unified Thread Standard for nuts and bolts is ANSI/ASME B1.1 which was defined in 1935, 1949, 1989, and 2003.
- The ANSI-NSF International standards used for commercial kitchens, such as restaurants, cafeterias, delis, etc.
- The ANSI/APSP (Association of Pool & Spa Professionals) standards used for pools, spas, hot tubs, barriers, and suction entrapment avoidance.
- The ANSI/HI (Hydraulic Institute) standards used for pumps.
- The ANSI for eye protection is Z87.1, which gives a specific impact resistance rating to the eyewear. This standard is commonly used for shop glasses, shooting glasses, and many other examples of protective eyewear. While compliance to this standard is required by United States federal law, it is not made freely available by ANSI, who charges \$65 to read a PDF of it.
- The ANSI paper sizes (ANSI/ASME Y14.1)
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+----------------------------------+
| ↓ Period |
+==================================+
| 2 |
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| 3 |
+----------------------------------+
| 4 |
+----------------------------------+
| 5 |
+----------------------------------+
| 6 |
+----------------------------------+
| 7 |
+----------------------------------+
| *Legend* |
| |
| ------------------------------ |
| primordial |
| element by radioactive decay |
| ------------------------------ |
+----------------------------------+
The **alkali metals** consist of the chemical elements lithium (Li), sodium (Na), potassium (K), rubidium (Rb), caesium (Cs),`{{refn|''Caesium'' is the spelling recommended by the [[International Union of Pure and Applied Chemistry]] (IUPAC).<ref>{{RedBook2005|pages=248–49}}.</ref> The [[American Chemical Society]] (ACS) has used the spelling ''cesium'' since 1921,<ref>{{cite book |editor1-first= Anne M. |editor1-last= Coghill |editor2-first= Lorrin R. |editor2-last= Garson |year= 2006 |title= The ACS Style Guide: Effective Communication of Scientific Information |edition= 3rd |publisher= American Chemical Society |location= Washington, D.C. |isbn= 978-0-8412-3999-9 |page= [https://archive.org/details/acsstyleguideeff0000unse/page/127 127] |url= https://archive.org/details/acsstyleguideeff0000unse/page/127 }}</ref><ref>{{cite journal |journal=Pure Appl. Chem. |volume=70 |issue=1 |last1=Coplen |pages= 237–257 |year= 1998 |first1=T. B. |url= http://old.iupac.org/reports/1998/7001coplen/history.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://old.iupac.org/reports/1998/7001coplen/history.pdf |archive-date=2022-10-09 |url-status=live |last2=Peiser |first2=H. S. |title= History of the recommended atomic-weight values from 1882 to 1997: a comparison of differences from current values to the estimated uncertainties of earlier values |doi= 10.1351/pac199870010237|s2cid=96729044 }}</ref> following ''Webster's Third New International Dictionary''.|group=note}}`{=mediawiki} and francium (Fr). Together with hydrogen they constitute group 1,`{{refn|In both the old IUPAC and the [[Chemical Abstracts Service|CAS]] systems for group numbering, this group is known as '''group IA''' (pronounced as "group one A", as the "I" is a [[Roman numeral]]).<ref name = fluck>{{cite journal |last1=Fluck |first1=E. |year=1988 |title=New Notations in the Periodic Table |journal=[[Pure Appl. Chem.]] |volume=60 |issue=3 |pages=431–436 |publisher=[[IUPAC]] |doi=10.1351/pac198860030431 |s2cid=96704008 |url=http://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://www.iupac.org/publications/pac/1988/pdf/6003x0431.pdf |archive-date=2022-10-09 |url-status=live |access-date=24 March 2012}}</ref>|name=group-numbering|group=note}}`{=mediawiki} which lies in the s-block of the periodic table. All alkali metals have their outermost electron in an s-orbital: this shared electron configuration results in their having very similar characteristic properties.`{{refn|While hydrogen also has this electron configuration, it is not considered an alkali metal as it has very different behaviour owing to the lack of [[valence electron|valence]] p-orbitals in [[period 1 element]]s.|group=note}}`{=mediawiki} Indeed, the alkali metals provide the best example of group trends in properties in the periodic table, with elements exhibiting well-characterised homologous behaviour. This family of elements is also known as the **lithium family** after its leading element.
The alkali metals are all shiny, soft, highly reactive metals at standard temperature and pressure and readily lose their outermost electron to form cations with charge +1. They can all be cut easily with a knife due to their softness, exposing a shiny surface that tarnishes rapidly in air due to oxidation by atmospheric moisture and oxygen (and in the case of lithium, nitrogen). Because of their high reactivity, they must be stored under oil to prevent reaction with air, and are found naturally only in salts and never as the free elements. Caesium, the fifth alkali metal, is the most reactive of all the metals. All the alkali metals react with water, with the heavier alkali metals reacting more vigorously than the lighter ones.
All of the discovered alkali metals occur in nature as their compounds: in order of abundance, sodium is the most abundant, followed by potassium, lithium, rubidium, caesium, and finally francium, which is very rare due to its extremely high radioactivity; francium occurs only in minute traces in nature as an intermediate step in some obscure side branches of the natural decay chains. Experiments have been conducted to attempt the synthesis of element 119, which is likely to be the next member of the group; none were successful. However, ununennium may not be an alkali metal due to relativistic effects, which are predicted to have a large influence on the chemical properties of superheavy elements; even if it does turn out to be an alkali metal, it is predicted to have some differences in physical and chemical properties from its lighter homologues.
Most alkali metals have many different applications. One of the best-known applications of the pure elements is the use of rubidium and caesium in atomic clocks, of which caesium atomic clocks form the basis of the second. A common application of the compounds of sodium is the sodium-vapour lamp, which emits light very efficiently. Table salt, or sodium chloride, has been used since antiquity. Lithium finds use as a psychiatric medication and as an anode in lithium batteries. Sodium, potassium and possibly lithium are essential elements, having major biological roles as electrolytes, and although the other alkali metals are not essential, they also have various effects on the body, both beneficial and harmful. \_\_TOC\_\_ `{{clear left}}`{=mediawiki}
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## History
Sodium compounds have been known since ancient times; salt (sodium chloride) has been an important commodity in human activities. While potash has been used since ancient times, it was not understood for most of its history to be a fundamentally different substance from sodium mineral salts. Georg Ernst Stahl obtained experimental evidence which led him to suggest the fundamental difference of sodium and potassium salts in 1702, and Henri-Louis Duhamel du Monceau was able to prove this difference in 1736. The exact chemical composition of potassium and sodium compounds, and the status as chemical element of potassium and sodium, was not known then, and thus Antoine Lavoisier did not include either alkali in his list of chemical elements in 1789.
Pure potassium was first isolated in 1807 in England by Humphry Davy, who derived it from caustic potash (KOH, potassium hydroxide) by the use of electrolysis of the molten salt with the newly invented voltaic pile. Previous attempts at electrolysis of the aqueous salt were unsuccessful due to potassium\'s extreme reactivity. Potassium was the first metal that was isolated by electrolysis. Later that same year, Davy reported extraction of sodium from the similar substance caustic soda (NaOH, lye) by a similar technique, demonstrating the elements, and thus the salts, to be different.
Petalite (`{{chem2|LiAlSi4O10|auto=yes}}`{=mediawiki}) was discovered in 1800 by the Brazilian chemist José Bonifácio de Andrada in a mine on the island of Utö, Sweden. However, it was not until 1817 that Johan August Arfwedson, then working in the laboratory of the chemist Jöns Jacob Berzelius, detected the presence of a new element while analysing petalite ore. This new element was noted by him to form compounds similar to those of sodium and potassium, though its carbonate and hydroxide were less soluble in water and more alkaline than the other alkali metals. Berzelius gave the unknown material the name *lithion*/*lithina*, from the Greek word *λιθoς* (transliterated as *lithos*, meaning \"stone\"), to reflect its discovery in a solid mineral, as opposed to potassium, which had been discovered in plant ashes, and sodium, which was known partly for its high abundance in animal blood. He named the metal inside the material *lithium*. Lithium, sodium, and potassium were part of the discovery of periodicity, as they are among a series of triads of elements in the same group that were noted by Johann Wolfgang Döbereiner in 1850 as having similar properties.
Rubidium and caesium were the first elements to be discovered using the spectroscope, invented in 1859 by Robert Bunsen and Gustav Kirchhoff. The next year, they discovered caesium in the mineral water from Bad Dürkheim, Germany. Their discovery of rubidium came the following year in Heidelberg, Germany, finding it in the mineral lepidolite. The names of rubidium and caesium come from the most prominent lines in their emission spectra: a bright red line for rubidium (from the Latin word *rubidus*, meaning dark red or bright red), and a sky-blue line for caesium (derived from the Latin word *caesius*, meaning sky-blue).
Around 1865 John Newlands produced a series of papers where he listed the elements in order of increasing atomic weight and similar physical and chemical properties that recurred at intervals of eight; he likened such periodicity to the octaves of music, where notes an octave apart have similar musical functions. His version put all the alkali metals then known (lithium to caesium), as well as copper, silver, and thallium (which show the +1 oxidation state characteristic of the alkali metals), together into a group. His table placed hydrogen with the halogens.
thumb\|upright=1.75\|Dmitri Mendeleev\'s periodic system proposed in 1871 showing hydrogen and the alkali metals as part of his group I, along with copper, silver, and gold After 1869, Dmitri Mendeleev proposed his periodic table placing lithium at the top of a group with sodium, potassium, rubidium, caesium, and thallium. Two years later, Mendeleev revised his table, placing hydrogen in group 1 above lithium, and also moving thallium to the boron group. In this 1871 version, copper, silver, and gold were placed twice, once as part of group IB, and once as part of a \"group VIII\" encompassing today\'s groups 8 to 11. After the introduction of the 18-column table, the group IB elements were moved to their current position in the d-block, while alkali metals were left in *group IA*. Later the group\'s name was changed to *group 1* in 1988. The trivial name \"alkali metals\" comes from the fact that the hydroxides of the group 1 elements are all strong alkalis when dissolved in water.
There were at least four erroneous and incomplete discoveries before Marguerite Perey of the Curie Institute in Paris, France discovered francium in 1939 by purifying a sample of actinium-227, which had been reported to have a decay energy of 220 keV. However, Perey noticed decay particles with an energy level below 80 keV. Perey thought this decay activity might have been caused by a previously unidentified decay product, one that was separated during purification, but emerged again out of the pure actinium-227. Various tests eliminated the possibility of the unknown element being thorium, radium, lead, bismuth, or thallium. The new product exhibited chemical properties of an alkali metal (such as coprecipitating with caesium salts), which led Perey to believe that it was element 87, caused by the alpha decay of actinium-227. Perey then attempted to determine the proportion of beta decay to alpha decay in actinium-227. Her first test put the alpha branching at 0.6%, a figure that she later revised to 1%.
: `{{overunderset|→|α (1.38%)|21.77 y}}`{=mediawiki} **`{{nuclide|francium|223}}`{=mediawiki}** `{{overunderset|→|β<sup>−</sup>|22 min}}`{=mediawiki} `{{nuclide|radium|223}}`{=mediawiki} `{{overunderset|→|α|11.4 d}}`{=mediawiki}`{{nuclide|radon|219}}`{=mediawiki}
The next element below francium (eka-francium) in the periodic table would be ununennium (Uue), element 119. The synthesis of ununennium was first attempted in 1985 by bombarding a target of einsteinium-254 with calcium-48 ions at the superHILAC accelerator at the Lawrence Berkeley National Laboratory in Berkeley, California. No atoms were identified, leading to a limiting yield of 300 nb.
: \+ `{{nuclide|calcium|48|link=y}}`{=mediawiki} → `{{nuclide|ununennium|302}}`{=mediawiki}\* → *no atoms*
It is highly unlikely that this reaction will be able to create any atoms of ununennium in the near future, given the extremely difficult task of making sufficient amounts of einsteinium-254, which is favoured for production of ultraheavy elements because of its large mass, relatively long half-life of 270 days, and availability in significant amounts of several micrograms, to make a large enough target to increase the sensitivity of the experiment to the required level; einsteinium has not been found in nature and has only been produced in laboratories, and in quantities smaller than those needed for effective synthesis of superheavy elements. However, given that ununennium is only the first period 8 element on the extended periodic table, it may well be discovered in the near future through other reactions, and indeed an attempt to synthesise it is currently ongoing in Japan. Currently, none of the period 8 elements has been discovered yet, and it is also possible, due to drip instabilities, that only the lower period 8 elements, up to around element 128, are physically possible. No attempts at synthesis have been made for any heavier alkali metals: due to their extremely high atomic number, they would require new, more powerful methods and technology to make.
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## Occurrence
### In the Solar System {#in_the_solar_system}
thumb\|upright=2.5\|Estimated abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, from the Big Bang. The next three elements (lithium, beryllium, and boron) are rare because they are poorly synthesised in the Big Bang and also in stars. The two general trends in the remaining stellar-produced elements are: (1) an alternation of abundance in elements as they have even or odd atomic numbers, and (2) a general decrease in abundance, as elements become heavier. Iron is especially common because it represents the minimum-energy nuclide that can be made by fusion of helium in supernovae. The Oddo--Harkins rule holds that elements with even atomic numbers are more common that those with odd atomic numbers, with the exception of hydrogen. This rule argues that elements with odd atomic numbers have one unpaired proton and are more likely to capture another, thus increasing their atomic number. In elements with even atomic numbers, protons are paired, with each member of the pair offsetting the spin of the other, enhancing stability. All the alkali metals have odd atomic numbers and they are not as common as the elements with even atomic numbers adjacent to them (the noble gases and the alkaline earth metals) in the Solar System. The heavier alkali metals are also less abundant than the lighter ones as the alkali metals from rubidium onward can only be synthesised in supernovae and not in stellar nucleosynthesis. Lithium is also much less abundant than sodium and potassium as it is poorly synthesised in both Big Bang nucleosynthesis and in stars: the Big Bang could only produce trace quantities of lithium, beryllium and boron due to the absence of a stable nucleus with 5 or 8 nucleons, and stellar nucleosynthesis could only pass this bottleneck by the triple-alpha process, fusing three helium nuclei to form carbon, and skipping over those three elements.
### On Earth {#on_earth}
The Earth formed from the same cloud of matter that formed the Sun, but the planets acquired different compositions during the formation and evolution of the Solar System. In turn, the natural history of the Earth caused parts of this planet to have differing concentrations of the elements. The mass of the Earth is approximately 5.98`{{e|24}}`{=mediawiki} kg. It is composed mostly of iron (32.1%), oxygen (30.1%), silicon (15.1%), magnesium (13.9%), sulfur (2.9%), nickel (1.8%), calcium (1.5%), and aluminium (1.4%); with the remaining 1.2% consisting of trace amounts of other elements. Due to planetary differentiation, the core region is believed to be primarily composed of iron (88.8%), with smaller amounts of nickel (5.8%), sulfur (4.5%), and less than 1% trace elements.
The alkali metals, due to their high reactivity, do not occur naturally in pure form in nature. They are lithophiles and therefore remain close to the Earth\'s surface because they combine readily with oxygen and so associate strongly with silica, forming relatively low-density minerals that do not sink down into the Earth\'s core. Potassium, rubidium and caesium are also incompatible elements due to their large ionic radii.
Sodium and potassium are very abundant on Earth, both being among the ten most common elements in Earth\'s crust; sodium makes up approximately 2.6% of the Earth\'s crust measured by weight, making it the sixth most abundant element overall and the most abundant alkali metal. Potassium makes up approximately 1.5% of the Earth\'s crust and is the seventh most abundant element. Sodium is found in many different minerals, of which the most common is ordinary salt (sodium chloride), which occurs in vast quantities dissolved in seawater. Other solid deposits include halite, amphibole, cryolite, nitratine, and zeolite. Many of these solid deposits occur as a result of ancient seas evaporating, which still occurs now in places such as Utah\'s Great Salt Lake and the Dead Sea. Despite their near-equal abundance in Earth\'s crust, sodium is far more common than potassium in the ocean, both because potassium\'s larger size makes its salts less soluble, and because potassium is bound by silicates in soil and what potassium leaches is absorbed far more readily by plant life than sodium.
Despite its chemical similarity, lithium typically does not occur together with sodium or potassium due to its smaller size. Due to its relatively low reactivity, it can be found in seawater in large amounts; it is estimated that lithium concentration in seawater is approximately 0.14 to 0.25 parts per million (ppm) or 25 micromolar. Its diagonal relationship with magnesium often allows it to replace magnesium in ferromagnesium minerals, where its crustal concentration is about 18 ppm, comparable to that of gallium and niobium. Commercially, the most important lithium mineral is spodumene, which occurs in large deposits worldwide.
Rubidium is approximately as abundant as zinc and more abundant than copper. It occurs naturally in the minerals leucite, pollucite, carnallite, zinnwaldite, and lepidolite, although none of these contain only rubidium and no other alkali metals. Caesium is more abundant than some commonly known elements, such as antimony, cadmium, tin, and tungsten, but is much less abundant than rubidium.
Francium-223, the only naturally occurring isotope of francium, is the product of the alpha decay of actinium-227 and can be found in trace amounts in uranium minerals. In a given sample of uranium, there is estimated to be only one francium atom for every 10^18^ uranium atoms. It has been calculated that there are at most 30 grams of francium in the earth\'s crust at any time, due to its extremely short half-life of 22 minutes.
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## Properties
### Physical and chemical {#physical_and_chemical}
The physical and chemical properties of the alkali metals can be readily explained by their having an ns^1^ valence electron configuration, which results in weak metallic bonding. Hence, all the alkali metals are soft and have low densities, melting and boiling points, as well as heats of sublimation, vaporisation, and dissociation. They all crystallise in the body-centered cubic crystal structure, and have distinctive flame colours because their outer s electron is very easily excited. Indeed, these flame test colours are the most common way of identifying them since all their salts with common ions are soluble. The ns^1^ configuration also results in the alkali metals having very large atomic and ionic radii, as well as very high thermal and electrical conductivity. Their chemistry is dominated by the loss of their lone valence electron in the outermost s-orbital to form the +1 oxidation state, due to the ease of ionising this electron and the very high second ionisation energy. Most of the chemistry has been observed only for the first five members of the group. The chemistry of francium is not well established due to its extreme radioactivity; thus, the presentation of its properties here is limited. What little is known about francium shows that it is very close in behaviour to caesium, as expected. The physical properties of francium are even sketchier because the bulk element has never been observed; hence any data that may be found in the literature are certainly speculative extrapolations.
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Name | Lithium | Sodium | Potassium | Rubidium | Caesium | Francium |
+==================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+==========================================================================================================================================================================================================================================================+================+==============+==============+================+==============================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+
| Atomic number | 3 | 11 | 19 | 37 | 55 | 87 |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Standard atomic weight`{{refn|The number given in [[bracket|parentheses]] refers to the [[standard uncertainty|measurement uncertainty]]. This uncertainty applies to the [[significant figure|least significant figure]](s) of the number prior to the parenthesised value (ie. counting from rightmost digit to left). For instance, {{val|1.00794|(7)}} stands for {{val|1.00794|0.00007}}, while {{val|1.00794|(72)}} stands for {{val|1.00794|0.00072}}.<ref>{{cite web|url=http://physics.nist.gov/cgi-bin/cuu/Info/Constants/definitions.html|title=Standard Uncertainty and Relative Standard Uncertainty|work=[[CODATA]] reference|publisher=[[National Institute of Standards and Technology]]|access-date=26 September 2011|archive-date=16 October 2011|archive-url=https://web.archive.org/web/20111016021440/http://physics.nist.gov/cgi-bin/cuu/Info/Constants/definitions.html|url-status=live}}</ref>|group=note}}`{=mediawiki} | 6.94(1)`{{refn|The value listed is the conventional value suitable for trade and commerce; the actual value may range from 6.938 to 6.997 depending on the isotopic composition of the sample.<ref name="atomicweights2009" />|group=note}}`{=mediawiki} | 22.98976928(2) | 39.0983(1) | 85.4678(3) | 132.9054519(2) | \[223\]`{{refn|The element does not have any stable [[nuclide]]s, and a value in brackets indicates the [[mass number]] of the longest-lived [[isotope]] of the element.<ref name="atomicweights2007" /><ref name="atomicweights2009" />|group=note}}`{=mediawiki} |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Electron configuration | \[He\] 2s^1^ | \[Ne\] 3s^1^ | \[Ar\] 4s^1^ | \[Kr\] 5s^1^ | \[Xe\] 6s^1^ | \[Rn\] 7s^1^ |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Melting point (°C) | 180.54 | 97.72 | 63.38 | 39.31 | 28.44 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Boiling point (°C) | 1342 | 883 | 759 | 688 | 671 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Density (g·cm^−3^) | 0.534 | 0.968 | 0.89 | 1.532 | 1.93 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Heat of fusion (kJ·mol^−1^) | 3.00 | 2.60 | 2.321 | 2.19 | 2.09 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Heat of vaporisation (kJ·mol^−1^) | 136 | 97.42 | 79.1 | 69 | 66.1 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Heat of formation of monatomic gas (kJ·mol^−1^) | 162 | 108 | 89.6 | 82.0 | 78.2 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Electrical resistivity at 25 °C (nΩ·cm) | 94.7 | 48.8 | 73.9 | 131 | 208 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Atomic radius (pm) | 152 | 186 | 227 | 248 | 265 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Ionic radius of hexacoordinate M^+^ ion (pm) | 76 | 102 | 138 | 152 | 167 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| First ionisation energy (kJ·mol^−1^) | 520.2 | 495.8 | 418.8 | 403.0 | 375.7 | 392.8 |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Electron affinity (kJ·mol^−1^) | 59.62 | 52.87 | 48.38 | 46.89 | 45.51 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Enthalpy of dissociation of M~2~ (kJ·mol^−1^) | 106.5 | 73.6 | 57.3 | 45.6 | 44.77 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Pauling electronegativity | 0.98 | 0.93 | 0.82 | 0.82 | 0.79 | ?`{{refn|[[Linus Pauling]] estimated the electronegativity of francium at 0.7 on the [[Pauling scale]], the same as caesium;<ref>{{cite book |last= Pauling |first= Linus |title= The Nature of the Chemical Bond|url= https://archive.org/details/natureofchemical00paul |url-access= registration |edition= Third |author-link= Linus Pauling |publisher= Cornell University Press |year= 1960 |isbn= 978-0-8014-0333-0 |page= [https://archive.org/details/natureofchemical00paul/page/93 93]}}</ref> the value for caesium has since been refined to 0.79, although there are no experimental data to allow a refinement of the value for francium.<ref>{{cite journal |last=Allred|first=A. L. |year= 1961 |journal= J. Inorg. Nucl. Chem.|volume= 17 |issue= 3–4 |pages= 215–221 |title= Electronegativity values from thermochemical data |doi= 10.1016/0022-1902(61)80142-5}}</ref> Francium has a slightly higher ionisation energy than caesium,<ref name="andreev" /> 392.811(4) kJ/mol as opposed to 375.7041(2) kJ/mol for caesium, as would be expected from [[relativistic effects]], and this would imply that caesium is the less electronegative of the two.|name=Fr-electronegativity|group=note}}`{=mediawiki} |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Allen electronegativity | 0.91 | 0.87 | 0.73 | 0.71 | 0.66 | 0.67 |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Standard electrode potential (*E*°(M^+^→M^0^); V) | −3.04 | −2.71 | −2.93 | −2.98 | −3.03 | ? |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Flame test colour\ | Crimson\ | Yellow\ | Violet\ | Red-violet\ | Blue\ | ? |
| Principal emission/absorption wavelength (nm) | 670.8 | 589.2 | 766.5 | 780.0 | 455.5 | |
+--------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+----------------+--------------+--------------+----------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
: Properties of the alkali metals
The alkali metals are more similar to each other than the elements in any other group are to each other. Indeed, the similarity is so great that it is quite difficult to separate potassium, rubidium, and caesium, due to their similar ionic radii; lithium and sodium are more distinct. For instance, when moving down the table, all known alkali metals show increasing atomic radius, decreasing electronegativity, increasing reactivity, and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their densities increase when moving down the table, with the exception that potassium is less dense than sodium. One of the very few properties of the alkali metals that does not display a very smooth trend is their reduction potentials: lithium\'s value is anomalous, being more negative than the others. This is because the Li^+^ ion has a very high hydration energy in the gas phase: though the lithium ion disrupts the structure of water significantly, causing a higher change in entropy, this high hydration energy is enough to make the reduction potentials indicate it as being the most electropositive alkali metal, despite the difficulty of ionising it in the gas phase.
The stable alkali metals are all silver-coloured metals except for caesium, which has a pale golden tint: it is one of only three metals that are clearly coloured (the other two being copper and gold). Additionally, the heavy alkaline earth metals calcium, strontium, and barium, as well as the divalent lanthanides europium and ytterbium, are pale yellow, though the colour is much less prominent than it is for caesium. Their lustre tarnishes rapidly in air due to oxidation.
| 1,178 |
Alkali metal
| 3 |
666 |
## Properties
### Physical and chemical {#physical_and_chemical}
All the alkali metals are highly reactive and are never found in elemental forms in nature. Because of this, they are usually stored in mineral oil or kerosene (paraffin oil). They react aggressively with the halogens to form the alkali metal halides, which are white ionic crystalline compounds that are all soluble in water except lithium fluoride (LiF). The alkali metals also react with water to form strongly alkaline hydroxides and thus should be handled with great care. The heavier alkali metals react more vigorously than the lighter ones; for example, when dropped into water, caesium produces a larger explosion than potassium if the same number of moles of each metal is used. The alkali metals have the lowest first ionisation energies in their respective periods of the periodic table because of their low effective nuclear charge and the ability to attain a noble gas configuration by losing just one electron. Not only do the alkali metals react with water, but also with proton donors like alcohols and phenols, gaseous ammonia, and alkynes, the last demonstrating the phenomenal degree of their reactivity. Their great power as reducing agents makes them very useful in liberating other metals from their oxides or halides.
The second ionisation energy of all of the alkali metals is very high as it is in a full shell that is also closer to the nucleus; thus, they almost always lose a single electron, forming cations. The alkalides are an exception: they are unstable compounds which contain alkali metals in a −1 oxidation state, which is very unusual as before the discovery of the alkalides, the alkali metals were not expected to be able to form anions and were thought to be able to appear in salts only as cations. The alkalide anions have filled s-subshells, which gives them enough stability to exist. All the stable alkali metals except lithium are known to be able to form alkalides, and the alkalides have much theoretical interest due to their unusual stoichiometry and low ionisation potentials. Alkalides are chemically similar to the electrides, which are salts with trapped electrons acting as anions. A particularly striking example of an alkalide is \"inverse sodium hydride\", H^+^Na^−^ (both ions being complexed), as opposed to the usual sodium hydride, Na^+^H^−^: it is unstable in isolation, due to its high energy resulting from the displacement of two electrons from hydrogen to sodium, although several derivatives are predicted to be metastable or stable.
In aqueous solution, the alkali metal ions form aqua ions of the formula \[M(H~2~O)~*n*~\]^+^, where *n* is the solvation number. Their coordination numbers and shapes agree well with those expected from their ionic radii. In aqueous solution the water molecules directly attached to the metal ion are said to belong to the first coordination sphere, also known as the first, or primary, solvation shell. The bond between a water molecule and the metal ion is a dative covalent bond, with the oxygen atom donating both electrons to the bond. Each coordinated water molecule may be attached by hydrogen bonds to other water molecules. The latter are said to reside in the second coordination sphere. However, for the alkali metal cations, the second coordination sphere is not well-defined as the +1 charge on the cation is not high enough to polarise the water molecules in the primary solvation shell enough for them to form strong hydrogen bonds with those in the second coordination sphere, producing a more stable entity. The solvation number for Li^+^ has been experimentally determined to be 4, forming the tetrahedral \[Li(H~2~O)~4~\]^+^: while solvation numbers of 3 to 6 have been found for lithium aqua ions, solvation numbers less than 4 may be the result of the formation of contact ion pairs, and the higher solvation numbers may be interpreted in terms of water molecules that approach \[Li(H~2~O)~4~\]^+^ through a face of the tetrahedron, though molecular dynamic simulations may indicate the existence of an octahedral hexaaqua ion. There are also probably six water molecules in the primary solvation sphere of the sodium ion, forming the octahedral \[Na(H~2~O)~6~\]^+^ ion. While it was previously thought that the heavier alkali metals also formed octahedral hexaaqua ions, it has since been found that potassium and rubidium probably form the \[K(H~2~O)~8~\]^+^ and \[Rb(H~2~O)~8~\]^+^ ions, which have the square antiprismatic structure, and that caesium forms the 12-coordinate \[Cs(H~2~O)~12~\]^+^ ion. `{{clear left}}`{=mediawiki}
#### Lithium
The chemistry of lithium shows several differences from that of the rest of the group as the small Li^+^ cation polarises anions and gives its compounds a more covalent character. Lithium and magnesium have a diagonal relationship due to their similar atomic radii, so that they show some similarities. For example, lithium forms a stable nitride, a property common among all the alkaline earth metals (magnesium\'s group) but unique among the alkali metals. In addition, among their respective groups, only lithium and magnesium form organometallic compounds with significant covalent character (e.g. LiMe and MgMe~2~).
Lithium fluoride is the only alkali metal halide that is poorly soluble in water, and lithium hydroxide is the only alkali metal hydroxide that is not deliquescent. Conversely, lithium perchlorate and other lithium salts with large anions that cannot be polarised are much more stable than the analogous compounds of the other alkali metals, probably because Li^+^ has a high solvation energy. This effect also means that most simple lithium salts are commonly encountered in hydrated form, because the anhydrous forms are extremely hygroscopic: this allows salts like lithium chloride and lithium bromide to be used in dehumidifiers and air-conditioners.
| 927 |
Alkali metal
| 4 |
666 |
## Properties
### Physical and chemical {#physical_and_chemical}
#### Francium
Francium is also predicted to show some differences due to its high atomic weight, causing its electrons to travel at considerable fractions of the speed of light and thus making relativistic effects more prominent. In contrast to the trend of decreasing electronegativities and ionisation energies of the alkali metals, francium\'s electronegativity and ionisation energy are predicted to be higher than caesium\'s due to the relativistic stabilisation of the 7s electrons; also, its atomic radius is expected to be abnormally low. Thus, contrary to expectation, caesium is the most reactive of the alkali metals, not francium. All known physical properties of francium also deviate from the clear trends going from lithium to caesium, such as the first ionisation energy, electron affinity, and anion polarisability, though due to the paucity of known data about francium many sources give extrapolated values, ignoring that relativistic effects make the trend from lithium to caesium become inapplicable at francium. Some of the few properties of francium that have been predicted taking relativity into account are the electron affinity (47.2 kJ/mol) and the enthalpy of dissociation of the Fr~2~ molecule (42.1 kJ/mol). The CsFr molecule is polarised as Cs^+^Fr^−^, showing that the 7s subshell of francium is much more strongly affected by relativistic effects than the 6s subshell of caesium. Additionally, francium superoxide (FrO~2~) is expected to have significant covalent character, unlike the other alkali metal superoxides, because of bonding contributions from the 6p electrons of francium.
| 249 |
Alkali metal
| 5 |
666 |
## Properties
### Nuclear
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| Z\ | Alkali metal\ | Stable\ | *Decays*\ | *unstable: italics* |
| | | | | |
| | | | | odd--odd isotopes coloured pink |
+==========================================================================================================================================================================================================================================================+===============+=========+===========+==========================================================================+
| 3 | lithium | 2 | --- | |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| 11 | sodium | 1 | --- | |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| 19 | potassium | 2 | 1 | |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| 37 | rubidium | 1 | 1 | |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| 55 | caesium | 1 | --- | |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| 87 | francium | --- | --- | *No primordial isotopes*\ |
| | | | | (*`{{SimpleNuclide|francium|223}}`{=mediawiki}* is a radiogenic nuclide) |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
| Radioactive: `{{nowrap|<sup>40</sup>K, [[half-life|t<sub>1/2</sub>]] 1.25 billion years;}}`{=mediawiki} `{{nowrap|<sup>87</sup>Rb, t<sub>1/2</sub> 49 billion years;}}`{=mediawiki} `{{nowrap|<sup>223</sup>Fr, t<sub>1/2</sub> 22.0 min.}}`{=mediawiki} | | | | |
+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+---------------+---------+-----------+--------------------------------------------------------------------------+
: Primordial isotopes of the alkali metals
All the alkali metals have odd atomic numbers; hence, their isotopes must be either odd--odd (both proton and neutron number are odd) or odd--even (proton number is odd, but neutron number is even). Odd--odd nuclei have even mass numbers, whereas odd--even nuclei have odd mass numbers. Odd--odd primordial nuclides are rare because most odd--odd nuclei are highly unstable with respect to beta decay, because the decay products are even--even, and are therefore more strongly bound, due to nuclear pairing effects.
Due to the great rarity of odd--odd nuclei, almost all the primordial isotopes of the alkali metals are odd--even (the exceptions being the light stable isotope lithium-6 and the long-lived radioisotope potassium-40). For a given odd mass number, there can be only a single beta-stable nuclide, since there is not a difference in binding energy between even--odd and odd--even comparable to that between even--even and odd--odd, leaving other nuclides of the same mass number (isobars) free to beta decay toward the lowest-mass nuclide. An effect of the instability of an odd number of either type of nucleons is that odd-numbered elements, such as the alkali metals, tend to have fewer stable isotopes than even-numbered elements. Of the 26 monoisotopic elements that have only a single stable isotope, all but one have an odd atomic number and all but one also have an even number of neutrons. Beryllium is the single exception to both rules, due to its low atomic number.
All of the alkali metals except lithium and caesium have at least one naturally occurring radioisotope: sodium-22 and sodium-24 are trace radioisotopes produced cosmogenically, potassium-40 and rubidium-87 have very long half-lives and thus occur naturally, and all isotopes of francium are radioactive. Caesium was also thought to be radioactive in the early 20th century, although it has no naturally occurring radioisotopes. (Francium had not been discovered yet at that time.) The natural long-lived radioisotope of potassium, potassium-40, makes up about 0.012% of natural potassium, and thus natural potassium is weakly radioactive. This natural radioactivity became a basis for a mistaken claim of the discovery for element 87 (the next alkali metal after caesium) in 1925. Natural rubidium is similarly slightly radioactive, with 27.83% being the long-lived radioisotope rubidium-87.
Caesium-137, with a half-life of 30.17 years, is one of the two principal medium-lived fission products, along with strontium-90, which are responsible for most of the radioactivity of spent nuclear fuel after several years of cooling, up to several hundred years after use. It constitutes most of the radioactivity still left from the Chernobyl accident. Caesium-137 undergoes high-energy beta decay and eventually becomes stable barium-137. It is a strong emitter of gamma radiation. Caesium-137 has a very low rate of neutron capture and cannot be feasibly disposed of in this way, but must be allowed to decay. Caesium-137 has been used as a tracer in hydrologic studies, analogous to the use of tritium. Small amounts of caesium-134 and caesium-137 were released into the environment during nearly all nuclear weapon tests and some nuclear accidents, most notably the Goiânia accident and the Chernobyl disaster. As of 2005, caesium-137 is the principal source of radiation in the zone of alienation around the Chernobyl nuclear power plant. Its chemical properties as one of the alkali metals make it one of the most problematic of the short-to-medium-lifetime fission products because it easily moves and spreads in nature due to the high water solubility of its salts, and is taken up by the body, which mistakes it for its essential congeners sodium and potassium.
| 731 |
Alkali metal
| 6 |
666 |
## Periodic trends {#periodic_trends}
The alkali metals are more similar to each other than the elements in any other group are to each other. For instance, when moving down the table, all known alkali metals show increasing atomic radius, decreasing electronegativity, increasing reactivity, and decreasing melting and boiling points as well as heats of fusion and vaporisation. In general, their densities increase when moving down the table, with the exception that potassium is less dense than sodium.
### Atomic and ionic radii {#atomic_and_ionic_radii}
The atomic radii of the alkali metals increase going down the group. Because of the shielding effect, when an atom has more than one electron shell, each electron feels electric repulsion from the other electrons as well as electric attraction from the nucleus. In the alkali metals, the outermost electron only feels a net charge of +1, as some of the nuclear charge (which is equal to the atomic number) is cancelled by the inner electrons; the number of inner electrons of an alkali metal is always one less than the nuclear charge. Therefore, the only factor which affects the atomic radius of the alkali metals is the number of electron shells. Since this number increases down the group, the atomic radius must also increase down the group.
The ionic radii of the alkali metals are much smaller than their atomic radii. This is because the outermost electron of the alkali metals is in a different electron shell than the inner electrons, and thus when it is removed the resulting atom has one fewer electron shell and is smaller. Additionally, the effective nuclear charge has increased, and thus the electrons are attracted more strongly towards the nucleus and the ionic radius decreases.
### First ionisation energy {#first_ionisation_energy}
thumb\|upright=2.7\|Periodic trend for ionisation energy: each period begins at a minimum for the alkali metals, and ends at a maximum for the noble gases. Predicted values are used for elements beyond 104. The first ionisation energy of an element or molecule is the energy required to move the most loosely held electron from one mole of gaseous atoms of the element or molecules to form one mole of gaseous ions with electric charge +1. The factors affecting the first ionisation energy are the nuclear charge, the amount of shielding by the inner electrons and the distance from the most loosely held electron from the nucleus, which is always an outer electron in main group elements. The first two factors change the effective nuclear charge the most loosely held electron feels. Since the outermost electron of alkali metals always feels the same effective nuclear charge (+1), the only factor which affects the first ionisation energy is the distance from the outermost electron to the nucleus. Since this distance increases down the group, the outermost electron feels less attraction from the nucleus and thus the first ionisation energy decreases. This trend is broken in francium due to the relativistic stabilisation and contraction of the 7s orbital, bringing francium\'s valence electron closer to the nucleus than would be expected from non-relativistic calculations. This makes francium\'s outermost electron feel more attraction from the nucleus, increasing its first ionisation energy slightly beyond that of caesium.
The second ionisation energy of the alkali metals is much higher than the first as the second-most loosely held electron is part of a fully filled electron shell and is thus difficult to remove.
### Reactivity
The reactivities of the alkali metals increase going down the group. This is the result of a combination of two factors: the first ionisation energies and atomisation energies of the alkali metals. Because the first ionisation energy of the alkali metals decreases down the group, it is easier for the outermost electron to be removed from the atom and participate in chemical reactions, thus increasing reactivity down the group. The atomisation energy measures the strength of the metallic bond of an element, which falls down the group as the atoms increase in radius and thus the metallic bond must increase in length, making the delocalised electrons further away from the attraction of the nuclei of the heavier alkali metals. Adding the atomisation and first ionisation energies gives a quantity closely related to (but not equal to) the activation energy of the reaction of an alkali metal with another substance. This quantity decreases going down the group, and so does the activation energy; thus, chemical reactions can occur faster and the reactivity increases down the group.
### Electronegativity
thumb\|upright=1.25\|Periodic variation of Pauling electronegativities as one descends the main groups of the periodic table from the second to the sixth period.
Electronegativity is a chemical property that describes the tendency of an atom or a functional group to attract electrons (or electron density) towards itself. If the bond between sodium and chlorine in sodium chloride were covalent, the pair of shared electrons would be attracted to the chlorine because the effective nuclear charge on the outer electrons is +7 in chlorine but is only +1 in sodium. The electron pair is attracted so close to the chlorine atom that they are practically transferred to the chlorine atom (an ionic bond). However, if the sodium atom was replaced by a lithium atom, the electrons will not be attracted as close to the chlorine atom as before because the lithium atom is smaller, making the electron pair more strongly attracted to the closer effective nuclear charge from lithium. Hence, the larger alkali metal atoms (further down the group) will be less electronegative as the bonding pair is less strongly attracted towards them. As mentioned previously, francium is expected to be an exception.
Because of the higher electronegativity of lithium, some of its compounds have a more covalent character. For example, lithium iodide (LiI) will dissolve in organic solvents, a property of most covalent compounds. Lithium fluoride (LiF) is the only alkali halide that is not soluble in water, and lithium hydroxide (LiOH) is the only alkali metal hydroxide that is not deliquescent.
| 994 |
Alkali metal
| 7 |
666 |
## Periodic trends {#periodic_trends}
### Melting and boiling points {#melting_and_boiling_points}
The melting point of a substance is the point where it changes state from solid to liquid while the boiling point of a substance (in liquid state) is the point where the vapour pressure of the liquid equals the environmental pressure surrounding the liquid and all the liquid changes state to gas. As a metal is heated to its melting point, the metallic bonds keeping the atoms in place weaken so that the atoms can move around, and the metallic bonds eventually break completely at the metal\'s boiling point. Therefore, the falling melting and boiling points of the alkali metals indicate that the strength of the metallic bonds of the alkali metals decreases down the group. This is because metal atoms are held together by the electromagnetic attraction from the positive ions to the delocalised electrons. As the atoms increase in size going down the group (because their atomic radius increases), the nuclei of the ions move further away from the delocalised electrons and hence the metallic bond becomes weaker so that the metal can more easily melt and boil, thus lowering the melting and boiling points. The increased nuclear charge is not a relevant factor due to the shielding effect.
### Density
The alkali metals all have the same crystal structure (body-centred cubic) and thus the only relevant factors are the number of atoms that can fit into a certain volume and the mass of one of the atoms, since density is defined as mass per unit volume. The first factor depends on the volume of the atom and thus the atomic radius, which increases going down the group; thus, the volume of an alkali metal atom increases going down the group. The mass of an alkali metal atom also increases going down the group. Thus, the trend for the densities of the alkali metals depends on their atomic weights and atomic radii; if figures for these two factors are known, the ratios between the densities of the alkali metals can then be calculated. The resultant trend is that the densities of the alkali metals increase down the table, with an exception at potassium. Due to having the lowest atomic weight and the largest atomic radius of all the elements in their periods, the alkali metals are the least dense metals in the periodic table. Lithium, sodium, and potassium are the only three metals in the periodic table that are less dense than water: in fact, lithium is the least dense known solid at room temperature.
| 427 |
Alkali metal
| 8 |
666 |
## Compounds
The alkali metals form complete series of compounds with all usually encountered anions, which well illustrate group trends. These compounds can be described as involving the alkali metals losing electrons to acceptor species and forming monopositive ions. This description is most accurate for alkali halides and becomes less and less accurate as cationic and anionic charge increase, and as the anion becomes larger and more polarisable. For instance, ionic bonding gives way to metallic bonding along the series NaCl, Na~2~O, Na~2~S, Na~3~P, Na~3~As, Na~3~Sb, Na~3~Bi, Na.
### Hydroxides
All the alkali metals react vigorously or explosively with cold water, producing an aqueous solution of a strongly basic alkali metal hydroxide and releasing hydrogen gas. This reaction becomes more vigorous going down the group: lithium reacts steadily with effervescence, but sodium and potassium can ignite, and rubidium and caesium sink in water and generate hydrogen gas so rapidly that shock waves form in the water that may shatter glass containers. When an alkali metal is dropped into water, it produces an explosion, of which there are two separate stages. The metal reacts with the water first, breaking the hydrogen bonds in the water and producing hydrogen gas; this takes place faster for the more reactive heavier alkali metals. Second, the heat generated by the first part of the reaction often ignites the hydrogen gas, causing it to burn explosively into the surrounding air. This secondary hydrogen gas explosion produces the visible flame above the bowl of water, lake or other body of water, not the initial reaction of the metal with water (which tends to happen mostly under water). The alkali metal hydroxides are the most basic known hydroxides.
Recent research has suggested that the explosive behavior of alkali metals in water is driven by a Coulomb explosion rather than solely by rapid generation of hydrogen itself. All alkali metals melt as a part of the reaction with water. Water molecules ionise the bare metallic surface of the liquid metal, leaving a positively charged metal surface and negatively charged water ions. The attraction between the charged metal and water ions will rapidly increase the surface area, causing an exponential increase of ionisation. When the repulsive forces within the liquid metal surface exceeds the forces of the surface tension, it vigorously explodes.
The hydroxides themselves are the most basic hydroxides known, reacting with acids to give salts and with alcohols to give oligomeric alkoxides. They easily react with carbon dioxide to form carbonates or bicarbonates, or with hydrogen sulfide to form sulfides or bisulfides, and may be used to separate thiols from petroleum. They react with amphoteric oxides: for example, the oxides of aluminium, zinc, tin, and lead react with the alkali metal hydroxides to give aluminates, zincates, stannates, and plumbates. Silicon dioxide is acidic, and thus the alkali metal hydroxides can also attack silicate glass.
### Intermetallic compounds {#intermetallic_compounds}
The alkali metals form many intermetallic compounds with each other and the elements from groups 2 to 13 in the periodic table of varying stoichiometries, such as the sodium amalgams with mercury, including Na~5~Hg~8~ and Na~3~Hg. Some of these have ionic characteristics: taking the alloys with gold, the most electronegative of metals, as an example, NaAu and KAu are metallic, but RbAu and CsAu are semiconductors. NaK is an alloy of sodium and potassium that is very useful because it is liquid at room temperature, although precautions must be taken due to its extreme reactivity towards water and air. The eutectic mixture melts at −12.6 °C. An alloy of 41% caesium, 47% sodium, and 12% potassium has the lowest known melting point of any metal or alloy, −78 °C.
### Compounds with the group 13 elements {#compounds_with_the_group_13_elements}
The intermetallic compounds of the alkali metals with the heavier group 13 elements (aluminium, gallium, indium, and thallium), such as NaTl, are poor conductors or semiconductors, unlike the normal alloys with the preceding elements, implying that the alkali metal involved has lost an electron to the Zintl anions involved. Nevertheless, while the elements in group 14 and beyond tend to form discrete anionic clusters, group 13 elements tend to form polymeric ions with the alkali metal cations located between the giant ionic lattice. For example, NaTl consists of a polymeric anion (---Tl^−^---)~n~ with a covalent diamond cubic structure with Na^+^ ions located between the anionic lattice. The larger alkali metals cannot fit similarly into an anionic lattice and tend to force the heavier group 13 elements to form anionic clusters.
Boron is a special case, being the only nonmetal in group 13. The alkali metal borides tend to be boron-rich, involving appreciable boron--boron bonding involving deltahedral structures, and are thermally unstable due to the alkali metals having a very high vapour pressure at elevated temperatures. This makes direct synthesis problematic because the alkali metals do not react with boron below 700 °C, and thus this must be accomplished in sealed containers with the alkali metal in excess. Furthermore, exceptionally in this group, reactivity with boron decreases down the group: lithium reacts completely at 700 °C, but sodium at 900 °C and potassium not until 1200 °C, and the reaction is instantaneous for lithium but takes hours for potassium. Rubidium and caesium borides have not even been characterised. Various phases are known, such as LiB~10~, NaB~6~, NaB~15~, and KB~6~. Under high pressure the boron--boron bonding in the lithium borides changes from following Wade\'s rules to forming Zintl anions like the rest of group 13.
| 910 |
Alkali metal
| 9 |
666 |
## Compounds
### Compounds with the group 14 elements {#compounds_with_the_group_14_elements}
Lithium and sodium react with carbon to form acetylides, Li~2~C~2~ and Na~2~C~2~, which can also be obtained by reaction of the metal with acetylene. Potassium, rubidium, and caesium react with graphite; their atoms are intercalated between the hexagonal graphite layers, forming graphite intercalation compounds of formulae MC~60~ (dark grey, almost black), MC~48~ (dark grey, almost black), MC~36~ (blue), MC~24~ (steel blue), and MC~8~ (bronze) (M = K, Rb, or Cs). These compounds are over 200 times more electrically conductive than pure graphite, suggesting that the valence electron of the alkali metal is transferred to the graphite layers (e.g. `{{chem2|M+C8-}}`{=mediawiki}). Upon heating of KC~8~, the elimination of potassium atoms results in the conversion in sequence to KC~24~, KC~36~, KC~48~ and finally KC~60~. KC~8~ is a very strong reducing agent and is pyrophoric and explodes on contact with water. While the larger alkali metals (K, Rb, and Cs) initially form MC~8~, the smaller ones initially form MC~6~, and indeed they require reaction of the metals with graphite at high temperatures around 500 °C to form. Apart from this, the alkali metals are such strong reducing agents that they can even reduce buckminsterfullerene to produce solid fullerides M~*n*~C~60~; sodium, potassium, rubidium, and caesium can form fullerides where *n* = 2, 3, 4, or 6, and rubidium and caesium additionally can achieve *n* = 1.
When the alkali metals react with the heavier elements in the carbon group (silicon, germanium, tin, and lead), ionic substances with cage-like structures are formed, such as the silicides M~4~Si~4~ (M = K, Rb, or Cs), which contains M^+^ and tetrahedral `{{chem2|Si4(4-)}}`{=mediawiki} ions. The chemistry of alkali metal germanides, involving the germanide ion Ge^4−^ and other cluster (Zintl) ions such as `{{chem2|Ge4(2-)}}`{=mediawiki}, `{{chem2|Ge9(4-)}}`{=mediawiki}, `{{chem2|Ge9(2-)}}`{=mediawiki}, and \[(Ge~9~)~2~\]^6−^, is largely analogous to that of the corresponding silicides. Alkali metal stannides are mostly ionic, sometimes with the stannide ion (Sn^4−^), and sometimes with more complex Zintl ions such as `{{chem2|Sn9(4-)}}`{=mediawiki}, which appears in tetrapotassium nonastannide (K~4~Sn~9~). The monatomic plumbide ion (Pb^4−^) is unknown, and indeed its formation is predicted to be energetically unfavourable; alkali metal plumbides have complex Zintl ions, such as `{{chem2|Pb9(4-)}}`{=mediawiki}. These alkali metal germanides, stannides, and plumbides may be produced by reducing germanium, tin, and lead with sodium metal in liquid ammonia.
| 383 |
Alkali metal
| 10 |
666 |
## Compounds
### Nitrides and pnictides {#nitrides_and_pnictides}
Lithium, the lightest of the alkali metals, is the only alkali metal which reacts with nitrogen at standard conditions, and its nitride is the only stable alkali metal nitride. Nitrogen is an unreactive gas because breaking the strong triple bond in the dinitrogen molecule (N~2~) requires a lot of energy. The formation of an alkali metal nitride would consume the ionisation energy of the alkali metal (forming M^+^ ions), the energy required to break the triple bond in N~2~ and the formation of N^3−^ ions, and all the energy released from the formation of an alkali metal nitride is from the lattice energy of the alkali metal nitride. The lattice energy is maximised with small, highly charged ions; the alkali metals do not form highly charged ions, only forming ions with a charge of +1, so only lithium, the smallest alkali metal, can release enough lattice energy to make the reaction with nitrogen exothermic, forming lithium nitride. The reactions of the other alkali metals with nitrogen would not release enough lattice energy and would thus be endothermic, so they do not form nitrides at standard conditions. Sodium nitride (Na~3~N) and potassium nitride (K~3~N), while existing, are extremely unstable, being prone to decomposing back into their constituent elements, and cannot be produced by reacting the elements with each other at standard conditions. Steric hindrance forbids the existence of rubidium or caesium nitride. However, sodium and potassium form colourless azide salts involving the linear `{{chem2|N3-}}`{=mediawiki} anion; due to the large size of the alkali metal cations, they are thermally stable enough to be able to melt before decomposing.
All the alkali metals react readily with phosphorus and arsenic to form phosphides and arsenides with the formula M~3~Pn (where M represents an alkali metal and Pn represents a pnictogen -- phosphorus, arsenic, antimony, or bismuth). This is due to the greater size of the P^3−^ and As^3−^ ions, so that less lattice energy needs to be released for the salts to form. These are not the only phosphides and arsenides of the alkali metals: for example, potassium has nine different known phosphides, with formulae K~3~P, K~4~P~3~, K~5~P~4~, KP, K~4~P~6~, K~3~P~7~, K~3~P~11~, KP~10.3~, and KP~15~. While most metals form arsenides, only the alkali and alkaline earth metals form mostly ionic arsenides. The structure of Na~3~As is complex with unusually short Na--Na distances of 328--330 pm which are shorter than in sodium metal, and this indicates that even with these electropositive metals the bonding cannot be straightforwardly ionic. Other alkali metal arsenides not conforming to the formula M~3~As are known, such as LiAs, which has a metallic lustre and electrical conductivity indicating the presence of some metallic bonding. The antimonides are unstable and reactive as the Sb^3−^ ion is a strong reducing agent; reaction of them with acids form the toxic and unstable gas stibine (SbH~3~). Indeed, they have some metallic properties, and the alkali metal antimonides of stoichiometry MSb involve antimony atoms bonded in a spiral Zintl structure. Bismuthides are not even wholly ionic; they are intermetallic compounds containing partially metallic and partially ionic bonds.
| 518 |
Alkali metal
| 11 |
666 |
## Compounds
### Oxides and chalcogenides {#oxides_and_chalcogenides}
All the alkali metals react vigorously with oxygen at standard conditions. They form various types of oxides, such as simple oxides (containing the O^2−^ ion), peroxides (containing the `{{chem2|O2(2-)}}`{=mediawiki} ion, where there is a single bond between the two oxygen atoms), superoxides (containing the `{{chem2|O2-}}`{=mediawiki} ion), and many others. Lithium burns in air to form lithium oxide, but sodium reacts with oxygen to form a mixture of sodium oxide and sodium peroxide. Potassium forms a mixture of potassium peroxide and potassium superoxide, while rubidium and caesium form the superoxide exclusively. Their reactivity increases going down the group: while lithium, sodium and potassium merely burn in air, rubidium and caesium are pyrophoric (spontaneously catch fire in air).
The smaller alkali metals tend to polarise the larger anions (the peroxide and superoxide) due to their small size. This attracts the electrons in the more complex anions towards one of its constituent oxygen atoms, forming an oxide ion and an oxygen atom. This causes lithium to form the oxide exclusively on reaction with oxygen at room temperature. This effect becomes drastically weaker for the larger sodium and potassium, allowing them to form the less stable peroxides. Rubidium and caesium, at the bottom of the group, are so large that even the least stable superoxides can form. Because the superoxide releases the most energy when formed, the superoxide is preferentially formed for the larger alkali metals where the more complex anions are not polarised. The oxides and peroxides for these alkali metals do exist, but do not form upon direct reaction of the metal with oxygen at standard conditions. In addition, the small size of the Li^+^ and O^2−^ ions contributes to their forming a stable ionic lattice structure. Under controlled conditions, however, all the alkali metals, with the exception of francium, are known to form their oxides, peroxides, and superoxides. The alkali metal peroxides and superoxides are powerful oxidising agents. Sodium peroxide and potassium superoxide react with carbon dioxide to form the alkali metal carbonate and oxygen gas, which allows them to be used in submarine air purifiers; the presence of water vapour, naturally present in breath, makes the removal of carbon dioxide by potassium superoxide even more efficient. All the stable alkali metals except lithium can form red ozonides (MO~3~) through low-temperature reaction of the powdered anhydrous hydroxide with ozone: the ozonides may be then extracted using liquid ammonia. They slowly decompose at standard conditions to the superoxides and oxygen, and hydrolyse immediately to the hydroxides when in contact with water. Potassium, rubidium, and caesium also form sesquioxides M~2~O~3~, which may be better considered peroxide disuperoxides, `{{chem2|[(M+)4(O2(2-))(O2-)2]}}`{=mediawiki}.
Rubidium and caesium can form a great variety of suboxides with the metals in formal oxidation states below +1. Rubidium can form Rb~6~O and Rb~9~O~2~ (copper-coloured) upon oxidation in air, while caesium forms an immense variety of oxides, such as the ozonide CsO~3~ and several brightly coloured suboxides, such as Cs~7~O (bronze), Cs~4~O (red-violet), Cs~11~O~3~ (violet), Cs~3~O (dark green), CsO, Cs~3~O~2~, as well as Cs~7~O~2~. The last of these may be heated under vacuum to generate Cs~2~O.
The alkali metals can also react analogously with the heavier chalcogens (sulfur, selenium, tellurium, and polonium), and all the alkali metal chalcogenides are known (with the exception of francium\'s). Reaction with an excess of the chalcogen can similarly result in lower chalcogenides, with chalcogen ions containing chains of the chalcogen atoms in question. For example, sodium can react with sulfur to form the sulfide (Na~2~S) and various polysulfides with the formula Na~2~S~*x*~ (*x* from 2 to 6), containing the `{{chem|S|''x''|2-}}`{=mediawiki} ions. Due to the basicity of the Se^2−^ and Te^2−^ ions, the alkali metal selenides and tellurides are alkaline in solution; when reacted directly with selenium and tellurium, alkali metal polyselenides and polytellurides are formed along with the selenides and tellurides with the `{{chem|Se|''x''|2-}}`{=mediawiki} and `{{chem|Te|''x''|2-}}`{=mediawiki} ions. They may be obtained directly from the elements in liquid ammonia or when air is not present, and are colourless, water-soluble compounds that air oxidises quickly back to selenium or tellurium. The alkali metal polonides are all ionic compounds containing the Po^2−^ ion; they are very chemically stable and can be produced by direct reaction of the elements at around 300--400 °C.
### Halides, hydrides, and pseudohalides {#halides_hydrides_and_pseudohalides}
The alkali metals are among the most electropositive elements on the periodic table and thus tend to bond ionically to the most electronegative elements on the periodic table, the halogens (fluorine, chlorine, bromine, iodine, and astatine), forming salts known as the alkali metal halides. The reaction is very vigorous and can sometimes result in explosions. All twenty stable alkali metal halides are known; the unstable ones are not known, with the exception of sodium astatide, because of the great instability and rarity of astatine and francium. The most well-known of the twenty is certainly sodium chloride, otherwise known as common salt. All of the stable alkali metal halides have the formula MX where M is an alkali metal and X is a halogen. They are all white ionic crystalline solids that have high melting points. All the alkali metal halides are soluble in water except for lithium fluoride (LiF), which is insoluble in water due to its very high lattice enthalpy. The high lattice enthalpy of lithium fluoride is due to the small sizes of the Li^+^ and F^−^ ions, causing the electrostatic interactions between them to be strong: a similar effect occurs for magnesium fluoride, consistent with the diagonal relationship between lithium and magnesium.
The alkali metals also react similarly with hydrogen to form ionic alkali metal hydrides, where the hydride anion acts as a pseudohalide: these are often used as reducing agents, producing hydrides, complex metal hydrides, or hydrogen gas. Other pseudohalides are also known, notably the cyanides. These are isostructural to the respective halides except for lithium cyanide, indicating that the cyanide ions may rotate freely. Ternary alkali metal halide oxides, such as Na~3~ClO, K~3~BrO (yellow), Na~4~Br~2~O, Na~4~I~2~O, and K~4~Br~2~O, are also known. The polyhalides are rather unstable, although those of rubidium and caesium are greatly stabilised by the feeble polarising power of these extremely large cations.
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Alkali metal
| 12 |
666 |
## Compounds
### Coordination complexes {#coordination_complexes}
Alkali metal cations do not usually form coordination complexes with simple Lewis bases due to their low charge of just +1 and their relatively large size; thus the Li^+^ ion forms most complexes and the heavier alkali metal ions form less and less (though exceptions occur for weak complexes). Lithium in particular has a very rich coordination chemistry in which it exhibits coordination numbers from 1 to 12, although octahedral hexacoordination is its preferred mode. In aqueous solution, the alkali metal ions exist as octahedral hexahydrate complexes \[M(H~2~O)~6~\]^+^, with the exception of the lithium ion, which due to its small size forms tetrahedral tetrahydrate complexes \[Li(H~2~O)~4~\]^+^; the alkali metals form these complexes because their ions are attracted by electrostatic forces of attraction to the polar water molecules. Because of this, anhydrous salts containing alkali metal cations are often used as desiccants. Alkali metals also readily form complexes with crown ethers (e.g. 12-crown-4 for Li^+^, 15-crown-5 for Na^+^, 18-crown-6 for K^+^, and 21-crown-7 for Rb^+^) and cryptands due to electrostatic attraction.
### Ammonia solutions {#ammonia_solutions}
The alkali metals dissolve slowly in liquid ammonia, forming ammoniacal solutions of solvated metal cation M^+^ and solvated electron e^−^, which react to form hydrogen gas and the alkali metal amide (MNH~2~, where M represents an alkali metal): this was first noted by Humphry Davy in 1809 and rediscovered by W. Weyl in 1864. The process may be speeded up by a catalyst. Similar solutions are formed by the heavy divalent alkaline earth metals calcium, strontium, barium, as well as the divalent lanthanides, europium and ytterbium. The amide salt is quite insoluble and readily precipitates out of solution, leaving intensely coloured ammonia solutions of the alkali metals. In 1907, Charles A. Kraus identified the colour as being due to the presence of solvated electrons, which contribute to the high electrical conductivity of these solutions. At low concentrations (below 3 M), the solution is dark blue and has ten times the conductivity of aqueous sodium chloride; at higher concentrations (above 3 M), the solution is copper-coloured and has approximately the conductivity of liquid metals like mercury. In addition to the alkali metal amide salt and solvated electrons, such ammonia solutions also contain the alkali metal cation (M^+^), the neutral alkali metal atom (M), diatomic alkali metal molecules (M~2~) and alkali metal anions (M^−^). These are unstable and eventually become the more thermodynamically stable alkali metal amide and hydrogen gas. Solvated electrons are powerful reducing agents and are often used in chemical synthesis.
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Alkali metal
| 13 |
666 |
## Compounds
### Organometallic
#### Organolithium
thumb\|upright=1.15\|Structure of the octahedral *n*-butyllithium hexamer, (C~4~H~9~Li)~6~. The aggregates are held together by delocalised covalent bonds between lithium and the terminal carbon of the butyl chain. There is no direct lithium--lithium bonding in any organolithium compound. thumb\|upright=1.15\|Solid phenyllithium forms monoclinic crystals that can be described as consisting of dimeric Li~2~(C~6~H~5~)~2~ subunits. The lithium atoms and the *ipso* carbons of the phenyl rings form a planar four-membered ring. The plane of the phenyl groups is perpendicular to the plane of this Li~2~C~2~ ring. Additional strong intermolecular bonding occurs between these phenyllithium dimers and the π electrons of the phenyl groups in the adjacent dimers, resulting in an infinite polymeric ladder structure.
Being the smallest alkali metal, lithium forms the widest variety of and most stable organometallic compounds, which are bonded covalently. Organolithium compounds are electrically non-conducting volatile solids or liquids that melt at low temperatures, and tend to form oligomers with the structure (RLi)~*x*~ where R is the organic group. As the electropositive nature of lithium puts most of the charge density of the bond on the carbon atom, effectively creating a carbanion, organolithium compounds are extremely powerful bases and nucleophiles. For use as bases, butyllithiums are often used and are commercially available. An example of an organolithium compound is methyllithium ((CH~3~Li)~*x*~), which exists in tetrameric (*x* = 4, tetrahedral) and hexameric (*x* = 6, octahedral) forms. Organolithium compounds, especially *n*-butyllithium, are useful reagents in organic synthesis, as might be expected given lithium\'s diagonal relationship with magnesium, which plays an important role in the Grignard reaction. For example, alkyllithiums and aryllithiums may be used to synthesise aldehydes and ketones by reaction with metal carbonyls. The reaction with nickel tetracarbonyl, for example, proceeds through an unstable acyl nickel carbonyl complex which then undergoes electrophilic substitution to give the desired aldehyde (using H^+^ as the electrophile) or ketone (using an alkyl halide) product.
: LiR \\ + \\ Ni(CO)4 \\ \\longrightarrow Li\^{+}\[RCONi(CO)3\]\^{-}
: Li\^{+}\[RCONi(CO)3\]\^{-}-\>\[\\ce{H\^{+}}\]\[\\ce{solvent}\] \\ Li\^{+} \\ + \\ RCHO \\ + \\ \[(solvent)Ni(CO)3\]
: Li\^{+}\[RCONi(CO)3\]\^{-}-\>\[\\ce{R\^{\'}Br}\]\[\\ce{solvent}\] \\ Li\^{+} \\ + \\ RR\^{\'}CO \\ + \\ \[(solvent)Ni(CO)3\]
Alkyllithiums and aryllithiums may also react with *N*,*N*-disubstituted amides to give aldehydes and ketones, and symmetrical ketones by reacting with carbon monoxide. They thermally decompose to eliminate a β-hydrogen, producing alkenes and lithium hydride: another route is the reaction of ethers with alkyl- and aryllithiums that act as strong bases. In non-polar solvents, aryllithiums react as the carbanions they effectively are, turning carbon dioxide to aromatic carboxylic acids (ArCO~2~H) and aryl ketones to tertiary carbinols (Ar\'~2~C(Ar)OH). Finally, they may be used to synthesise other organometallic compounds through metal-halogen exchange.
#### Heavier alkali metals {#heavier_alkali_metals}
Unlike the organolithium compounds, the organometallic compounds of the heavier alkali metals are predominantly ionic. The application of organosodium compounds in chemistry is limited in part due to competition from organolithium compounds, which are commercially available and exhibit more convenient reactivity. The principal organosodium compound of commercial importance is sodium cyclopentadienide. Sodium tetraphenylborate can also be classified as an organosodium compound since in the solid state sodium is bound to the aryl groups. Organometallic compounds of the higher alkali metals are even more reactive than organosodium compounds and of limited utility. A notable reagent is Schlosser\'s base, a mixture of *n*-butyllithium and potassium *tert*-butoxide. This reagent reacts with propene to form the compound allylpotassium (KCH~2~CHCH~2~). *cis*-2-Butene and *trans*-2-butene equilibrate when in contact with alkali metals. Whereas isomerisation is fast with lithium and sodium, it is slow with the heavier alkali metals. The heavier alkali metals also favour the sterically congested conformation. Several crystal structures of organopotassium compounds have been reported, establishing that they, like the sodium compounds, are polymeric. Organosodium, organopotassium, organorubidium and organocaesium compounds are all mostly ionic and are insoluble (or nearly so) in nonpolar solvents.
Alkyl and aryl derivatives of sodium and potassium tend to react with air. They cause the cleavage of ethers, generating alkoxides. Unlike alkyllithium compounds, alkylsodiums and alkylpotassiums cannot be made by reacting the metals with alkyl halides because Wurtz coupling occurs:
: RM + R\'X → R--R\' + MX
As such, they have to be made by reacting alkylmercury compounds with sodium or potassium metal in inert hydrocarbon solvents. While methylsodium forms tetramers like methyllithium, methylpotassium is more ionic and has the nickel arsenide structure with discrete methyl anions and potassium cations.
The alkali metals and their hydrides react with acidic hydrocarbons, for example cyclopentadienes and terminal alkynes, to give salts. Liquid ammonia, ether, or hydrocarbon solvents are used, the most common of which being tetrahydrofuran. The most important of these compounds is sodium cyclopentadienide, NaC~5~H~5~, an important precursor to many transition metal cyclopentadienyl derivatives. Similarly, the alkali metals react with cyclooctatetraene in tetrahydrofuran to give alkali metal cyclooctatetraenides; for example, dipotassium cyclooctatetraenide (K~2~C~8~H~8~) is an important precursor to many metal cyclooctatetraenyl derivatives, such as uranocene. The large and very weakly polarising alkali metal cations can stabilise large, aromatic, polarisable radical anions, such as the dark-green sodium naphthalenide, Na^+^\[C~10~H~8~•\]^−^, a strong reducing agent.
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## Representative reactions of alkali metals {#representative_reactions_of_alkali_metals}
### Reaction with oxygen {#reaction_with_oxygen}
Upon reacting with oxygen, alkali metals form oxides, peroxides, superoxides and suboxides. However, the first three are more common. The table below shows the types of compounds formed in reaction with oxygen. The compound in brackets represents the minor product of combustion.
------------------ ----------- -------------- ----------------
**Alkali metal** **Oxide** **Peroxide** **Superoxide**
Li Li~2~O (Li~2~O~2~)
Na (Na~2~O) Na~2~O~2~
K KO~2~
Rb RbO~2~
Cs CsO~2~
------------------ ----------- -------------- ----------------
The alkali metal peroxides are ionic compounds that are unstable in water. The peroxide anion is weakly bound to the cation, and it is hydrolysed, forming stronger covalent bonds.
: Na~2~O~2~ + 2H~2~O → 2NaOH + H~2~O~2~
The other oxygen compounds are also unstable in water.
: 2KO~2~ + 2H~2~O → 2KOH + H~2~O~2~ + O~2~
: Li~2~O + H~2~O → 2LiOH
### Reaction with sulfur {#reaction_with_sulfur}
With sulfur, they form sulfides and polysulfides.
: 2Na + 1/8S~8~ → Na~2~S + 1/8S~8~ → Na~2~S~2~\...Na~2~S~7~
Because alkali metal sulfides are essentially salts of a weak acid and a strong base, they form basic solutions.
: S^2-^ + H~2~O → HS^−^ + HO^−^
: HS^−^ + H~2~O → H~2~S + HO^−^
### Reaction with nitrogen {#reaction_with_nitrogen}
Lithium is the only metal that combines directly with nitrogen at room temperature.
: 3Li + 1/2N~2~ → Li~3~N
Li~3~N can react with water to liberate ammonia.
: Li~3~N + 3H~2~O → 3LiOH + NH~3~
### Reaction with hydrogen {#reaction_with_hydrogen}
With hydrogen, alkali metals form saline hydrides that hydrolyse in water.
: 2 Na \\ + H2 \\ -\>\[\\ce{\\Delta}\] \\ 2 NaH
: 2 NaH \\ + \\ 2 H2O \\ \\longrightarrow \\ 2 NaOH \\ + \\ H2 \\uparrow
### Reaction with carbon {#reaction_with_carbon}
Lithium is the only metal that reacts directly with carbon to give dilithium acetylide. Na and K can react with acetylene to give acetylides.
: 2 Li \\ + \\ 2 C \\ \\longrightarrow \\ Li2C2
: 2 Na \\ + \\ 2 C2H2 \\ -\>\[\\ce{150 \\ \^{o}C}\] \\ 2 NaC2H \\ + \\ H2
: 2 Na \\ + \\ 2 NaC2H \\ -\>\[\\ce{220 \\ \^{o}C}\] \\ 2 Na2C2 \\ + \\ H2
### Reaction with water {#reaction_with_water}
On reaction with water, they generate hydroxide ions and hydrogen gas. This reaction is vigorous and highly exothermic and the hydrogen resulted may ignite in air or even explode in the case of Rb and Cs.
: Na + H~2~O → NaOH + 1/2H~2~
### Reaction with other salts {#reaction_with_other_salts}
The alkali metals are very good reducing agents. They can reduce metal cations that are less electropositive. Titanium is produced industrially by the reduction of titanium tetrachloride with Na at 400 °C (van Arkel--de Boer process).
: TiCl~4~ + 4Na → 4NaCl + Ti
### Reaction with organohalide compounds {#reaction_with_organohalide_compounds}
Alkali metals react with halogen derivatives to generate hydrocarbon via the Wurtz reaction.
: 2CH~3~-Cl + 2Na → H~3~C-CH~3~ + 2NaCl
### Alkali metals in liquid ammonia {#alkali_metals_in_liquid_ammonia}
Alkali metals dissolve in liquid ammonia or other donor solvents like aliphatic amines or hexamethylphosphoramide to give blue solutions. These solutions are believed to contain free electrons.
: Na + xNH~3~ → Na^+^ + e(NH~3~)~x~^−^
Due to the presence of solvated electrons, these solutions are very powerful reducing agents used in organic synthesis.
thumb\|upright=1.25\|centre\|Reduction reactions using sodium in liquid ammonia
Reaction 1) is known as Birch reduction. Other reductions that can be carried by these solutions are:
: S~8~ + 2e^−^ → S~8~^2-^
: Fe(CO)~5~ + 2e^−^ → Fe(CO)~4~^2-^ + CO
| 586 |
Alkali metal
| 15 |
666 |
## Extensions
thumb\|upright=1.12\|Empirical (Na--Cs, Mg--Ra) and predicted (Fr--Uhp, Ubn--Uhh) atomic radius of the alkali and alkaline earth metals from the third to the ninth period, measured in angstroms Although francium is the heaviest alkali metal that has been discovered, there has been some theoretical work predicting the physical and chemical characteristics of hypothetical heavier alkali metals. Being the first period 8 element, the undiscovered element ununennium (element 119) is predicted to be the next alkali metal after francium and behave much like their lighter congeners; however, it is also predicted to differ from the lighter alkali metals in some properties. Its chemistry is predicted to be closer to that of potassium or rubidium instead of caesium or francium. This is unusual as periodic trends, ignoring relativistic effects would predict ununennium to be even more reactive than caesium and francium. This lowered reactivity is due to the relativistic stabilisation of ununennium\'s valence electron, increasing ununennium\'s first ionisation energy and decreasing the metallic and ionic radii; this effect is already seen for francium. This assumes that ununennium will behave chemically as an alkali metal, which, although likely, may not be true due to relativistic effects. The relativistic stabilisation of the 8s orbital also increases ununennium\'s electron affinity far beyond that of caesium and francium; indeed, ununennium is expected to have an electron affinity higher than all the alkali metals lighter than it. Relativistic effects also cause a very large drop in the polarisability of ununennium. On the other hand, ununennium is predicted to continue the trend of melting points decreasing going down the group, being expected to have a melting point between 0 °C and 30 °C.
The stabilisation of ununennium\'s valence electron and thus the contraction of the 8s orbital cause its atomic radius to be lowered to 240 pm, very close to that of rubidium (247 pm), so that the chemistry of ununennium in the +1 oxidation state should be more similar to the chemistry of rubidium than to that of francium. On the other hand, the ionic radius of the Uue^+^ ion is predicted to be larger than that of Rb^+^, because the 7p orbitals are destabilised and are thus larger than the p-orbitals of the lower shells. Ununennium may also show the +3 and +5 oxidation states, which are not seen in any other alkali metal, in addition to the +1 oxidation state that is characteristic of the other alkali metals and is also the main oxidation state of all the known alkali metals: this is because of the destabilisation and expansion of the 7p~3/2~ spinor, causing its outermost electrons to have a lower ionisation energy than what would otherwise be expected. Indeed, many ununennium compounds are expected to have a large covalent character, due to the involvement of the 7p~3/2~ electrons in the bonding.
Not as much work has been done predicting the properties of the alkali metals beyond ununennium. Although a simple extrapolation of the periodic table (by the Aufbau principle) would put element 169, unhexennium, under ununennium, Dirac-Fock calculations predict that the next element after ununennium with alkali-metal-like properties may be element 165, unhexpentium, which is predicted to have the electron configuration \[Og\] 5g^18^ 6f^14^ 7d^10^ 8s^2^ 8p~1/2~^2^ 9s^1^. This element would be intermediate in properties between an alkali metal and a group 11 element, and while its physical and atomic properties would be closer to the former, its chemistry may be closer to that of the latter. Further calculations show that unhexpentium would follow the trend of increasing ionisation energy beyond caesium, having an ionisation energy comparable to that of sodium, and that it should also continue the trend of decreasing atomic radii beyond caesium, having an atomic radius comparable to that of potassium. However, the 7d electrons of unhexpentium may also be able to participate in chemical reactions along with the 9s electron, possibly allowing oxidation states beyond +1, whence the likely transition metal behaviour of unhexpentium. Due to the alkali and alkaline earth metals both being s-block elements, these predictions for the trends and properties of ununennium and unhexpentium also mostly hold quite similarly for the corresponding alkaline earth metals unbinilium (Ubn) and unhexhexium (Uhh). Unsepttrium, element 173, may be an even better heavier homologue of ununennium; with a predicted electron configuration of \[Usb\] 6g^1^, it returns to the alkali-metal-like situation of having one easily removed electron far above a closed p-shell in energy, and is expected to be even more reactive than caesium.
The probable properties of further alkali metals beyond unsepttrium have not been explored yet as of 2019, and they may or may not be able to exist. In periods 8 and above of the periodic table, relativistic and shell-structure effects become so strong that extrapolations from lighter congeners become completely inaccurate. In addition, the relativistic and shell-structure effects (which stabilise the s-orbitals and destabilise and expand the d-, f-, and g-orbitals of higher shells) have opposite effects, causing even larger difference between relativistic and non-relativistic calculations of the properties of elements with such high atomic numbers. Interest in the chemical properties of ununennium, unhexpentium, and unsepttrium stems from the fact that they are located close to the expected locations of islands of stability, centered at elements 122 (^306^Ubb) and 164 (^482^Uhq).
| 873 |
Alkali metal
| 16 |
666 |
## Pseudo-alkali metals {#pseudo_alkali_metals}
Many other substances are similar to the alkali metals in their tendency to form monopositive cations. Analogously to the pseudohalogens, they have sometimes been called \"pseudo-alkali metals\". These substances include some elements and many more polyatomic ions; the polyatomic ions are especially similar to the alkali metals in their large size and weak polarising power.
### Hydrogen
The element hydrogen, with one electron per neutral atom, is usually placed at the top of Group 1 of the periodic table because of its electron configuration. But hydrogen is not normally considered to be an alkali metal. Metallic hydrogen, which only exists at very high pressures, is known for its electrical and magnetic properties, not its chemical properties. Under typical conditions, pure hydrogen exists as a diatomic gas consisting of two atoms per molecule (H~2~); however, the alkali metals form diatomic molecules (such as dilithium, Li~2~) only at high temperatures, when they are in the gaseous state.
Hydrogen, like the alkali metals, has one valence electron and reacts easily with the halogens, but the similarities mostly end there because of the small size of a bare proton H^+^ compared to the alkali metal cations. Its placement above lithium is primarily due to its electron configuration. It is sometimes placed above fluorine due to their similar chemical properties, though the resemblance is likewise not absolute.
The first ionisation energy of hydrogen (1312.0 kJ/mol) is much higher than that of the alkali metals. As only one additional electron is required to fill in the outermost shell of the hydrogen atom, hydrogen often behaves like a halogen, forming the negative hydride ion, and is very occasionally considered to be a halogen on that basis. (The alkali metals can also form negative ions, known as alkalides, but these are little more than laboratory curiosities, being unstable.) An argument against this placement is that formation of hydride from hydrogen is endothermic, unlike the exothermic formation of halides from halogens. The radius of the H^−^ anion also does not fit the trend of increasing size going down the halogens: indeed, H^−^ is very diffuse because its single proton cannot easily control both electrons. It was expected for some time that liquid hydrogen would show metallic properties; while this has been shown to not be the case, under extremely high pressures, such as those found at the cores of Jupiter and Saturn, hydrogen does become metallic and behaves like an alkali metal; in this phase, it is known as metallic hydrogen. The electrical resistivity of liquid metallic hydrogen at 3000 K is approximately equal to that of liquid rubidium and caesium at 2000 K at the respective pressures when they undergo a nonmetal-to-metal transition.
The 1s^1^ electron configuration of hydrogen, while analogous to that of the alkali metals (ns^1^), is unique because there is no 1p subshell. Hence it can lose an electron to form the hydron H^+^, or gain one to form the hydride ion H^−^. In the former case it resembles superficially the alkali metals; in the latter case, the halogens, but the differences due to the lack of a 1p subshell are important enough that neither group fits the properties of hydrogen well. Group 14 is also a good fit in terms of thermodynamic properties such as ionisation energy and electron affinity, but hydrogen cannot be tetravalent. Thus none of the three placements are entirely satisfactory, although group 1 is the most common placement (if one is chosen) because of the electron configuration and the fact that the hydron is by far the most important of all monatomic hydrogen species, being the foundation of acid-base chemistry. As an example of hydrogen\'s unorthodox properties stemming from its unusual electron configuration and small size, the hydrogen ion is very small (radius around 150 fm compared to the 50--220 pm size of most other atoms and ions) and so is nonexistent in condensed systems other than in association with other atoms or molecules. Indeed, transferring of protons between chemicals is the basis of acid-base chemistry. Also unique is hydrogen\'s ability to form hydrogen bonds, which are an effect of charge-transfer, electrostatic, and electron correlative contributing phenomena. While analogous lithium bonds are also known, they are mostly electrostatic. Nevertheless, hydrogen can take on the same structural role as the alkali metals in some molecular crystals, and has a close relationship with the lightest alkali metals (especially lithium).
### Ammonium and derivatives {#ammonium_and_derivatives}
The ammonium ion (`{{chem2|NH4+}}`{=mediawiki}) has very similar properties to the heavier alkali metals, acting as an alkali metal intermediate between potassium and rubidium, and is often considered a close relative. For example, most alkali metal salts are soluble in water, a property which ammonium salts share. Ammonium is expected to behave stably as a metal (`{{chem2|NH4+}}`{=mediawiki} ions in a sea of delocalised electrons) at very high pressures (though less than the typical pressure where transitions from insulating to metallic behaviour occur around, 100 GPa), and could possibly occur inside the ice giants Uranus and Neptune, which may have significant impacts on their interior magnetic fields. It has been estimated that the transition from a mixture of ammonia and dihydrogen molecules to metallic ammonium may occur at pressures just below 25 GPa. Under standard conditions, ammonium can form a metallic amalgam with mercury.
Other \"pseudo-alkali metals\" include the alkylammonium cations, in which some of the hydrogen atoms in the ammonium cation are replaced by alkyl or aryl groups. In particular, the quaternary ammonium cations (`{{chem2|NR4+}}`{=mediawiki}) are very useful since they are permanently charged, and they are often used as an alternative to the expensive Cs^+^ to stabilise very large and very easily polarisable anions such as `{{chem2|HI2-}}`{=mediawiki}. Tetraalkylammonium hydroxides, like alkali metal hydroxides, are very strong bases that react with atmospheric carbon dioxide to form carbonates. Furthermore, the nitrogen atom may be replaced by a phosphorus, arsenic, or antimony atom (the heavier nonmetallic pnictogens), creating a phosphonium (`{{chem2|PH4+}}`{=mediawiki}) or arsonium (`{{chem2|AsH4+}}`{=mediawiki}) cation that can itself be substituted similarly; while stibonium (`{{chem2|SbH4+}}`{=mediawiki}) itself is not known, some of its organic derivatives are characterised.
| 1,007 |
Alkali metal
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## Pseudo-alkali metals {#pseudo_alkali_metals}
### Cobaltocene and derivatives {#cobaltocene_and_derivatives}
Cobaltocene, Co(C~5~H~5~)~2~, is a metallocene, the cobalt analogue of ferrocene. It is a dark purple solid. Cobaltocene has 19 valence electrons, one more than usually found in organotransition metal complexes, such as its very stable relative, ferrocene, in accordance with the 18-electron rule. This additional electron occupies an orbital that is antibonding with respect to the Co--C bonds. Consequently, many chemical reactions of Co(C~5~H~5~)~2~ are characterized by its tendency to lose this \"extra\" electron, yielding a very stable 18-electron cation known as cobaltocenium. Many cobaltocenium salts coprecipitate with caesium salts, and cobaltocenium hydroxide is a strong base that absorbs atmospheric carbon dioxide to form cobaltocenium carbonate. Like the alkali metals, cobaltocene is a strong reducing agent, and decamethylcobaltocene is stronger still due to the combined inductive effect of the ten methyl groups. Cobalt may be substituted by its heavier congener rhodium to give rhodocene, an even stronger reducing agent. Iridocene (involving iridium) would presumably be still more potent, but is not very well-studied due to its instability.
### Thallium
Thallium is the heaviest stable element in group 13 of the periodic table. At the bottom of the periodic table, the inert-pair effect is quite strong, because of the relativistic stabilisation of the 6s orbital and the decreasing bond energy as the atoms increase in size so that the amount of energy released in forming two more bonds is not worth the high ionisation energies of the 6s electrons. It displays the +1 oxidation state that all the known alkali metals display, and thallium compounds with thallium in its +1 oxidation state closely resemble the corresponding potassium or silver compounds stoichiometrically due to the similar ionic radii of the Tl^+^ (164 pm), K^+^ (152 pm) and Ag^+^ (129 pm) ions. It was sometimes considered an alkali metal in continental Europe (but not in England) in the years immediately following its discovery, and was placed just after caesium as the sixth alkali metal in Dmitri Mendeleev\'s 1869 periodic table and Julius Lothar Meyer\'s 1868 periodic table. Mendeleev\'s 1871 periodic table and Meyer\'s 1870 periodic table put thallium in its current position in the boron group and left the space below caesium blank. However, thallium also displays the oxidation state +3, which no known alkali metal displays (although ununennium, the undiscovered seventh alkali metal, is predicted to possibly display the +3 oxidation state). The sixth alkali metal is now considered to be francium. While Tl^+^ is stabilised by the inert-pair effect, this inert pair of 6s electrons is still able to participate chemically, so that these electrons are stereochemically active in aqueous solution. Additionally, the thallium halides (except TlF) are quite insoluble in water, and TlI has an unusual structure because of the presence of the stereochemically active inert pair in thallium.
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## Pseudo-alkali metals {#pseudo_alkali_metals}
### Copper, silver, and gold {#copper_silver_and_gold}
The group 11 metals (or coinage metals), copper, silver, and gold, are typically categorised as transition metals given they can form ions with incomplete d-shells. Physically, they have the relatively low melting points and high electronegativity values associated with post-transition metals. \"The filled *d* subshell and free *s* electron of Cu, Ag, and Au contribute to their high electrical and thermal conductivity. Transition metals to the left of group 11 experience interactions between *s* electrons and the partially filled *d* subshell that lower electron mobility.\" Chemically, the group 11 metals behave like main-group metals in their +1 valence states, and are hence somewhat related to the alkali metals: this is one reason for their previously being labelled as \"group IB\", paralleling the alkali metals\' \"group IA\". They are occasionally classified as post-transition metals. Their spectra are analogous to those of the alkali metals. Their monopositive ions are paramagnetic and contribute no colour to their salts, like those of the alkali metals.
In Mendeleev\'s 1871 periodic table, copper, silver, and gold are listed twice, once under group VIII (with the iron triad and platinum group metals), and once under group IB. Group IB was nonetheless parenthesised to note that it was tentative. Mendeleev\'s main criterion for group assignment was the maximum oxidation state of an element: on that basis, the group 11 elements could not be classified in group IB, due to the existence of copper(II) and gold(III) compounds being known at that time. However, eliminating group IB would make group I the only main group (group VIII was labelled a transition group) to lack an A--B bifurcation. Soon afterward, a majority of chemists chose to classify these elements in group IB and remove them from group VIII for the resulting symmetry: this was the predominant classification until the rise of the modern medium-long 18-column periodic table, which separated the alkali metals and group 11 metals.
The coinage metals were traditionally regarded as a subdivision of the alkali metal group, due to them sharing the characteristic s^1^ electron configuration of the alkali metals (group 1: p^6^s^1^; group 11: d^10^s^1^). However, the similarities are largely confined to the stoichiometries of the +1 compounds of both groups, and not their chemical properties. This stems from the filled d subshell providing a much weaker shielding effect on the outermost s electron than the filled p subshell, so that the coinage metals have much higher first ionisation energies and smaller ionic radii than do the corresponding alkali metals. Furthermore, they have higher melting points, hardnesses, and densities, and lower reactivities and solubilities in liquid ammonia, as well as having more covalent character in their compounds. Finally, the alkali metals are at the top of the electrochemical series, whereas the coinage metals are almost at the very bottom. The coinage metals\' filled d shell is much more easily disrupted than the alkali metals\' filled p shell, so that the second and third ionisation energies are lower, enabling higher oxidation states than +1 and a richer coordination chemistry, thus giving the group 11 metals clear transition metal character. Particularly noteworthy is gold forming ionic compounds with rubidium and caesium, in which it forms the auride ion (Au^−^) which also occurs in solvated form in liquid ammonia solution: here gold behaves as a pseudohalogen because its 5d^10^6s^1^ configuration has one electron less than the quasi-closed shell 5d^10^6s^2^ configuration of mercury.
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666 |
## Production and isolation {#production_and_isolation}
The production of pure alkali metals is somewhat complicated due to their extreme reactivity with commonly used substances, such as water. From their silicate ores, all the stable alkali metals may be obtained the same way: sulfuric acid is first used to dissolve the desired alkali metal ion and aluminium(III) ions from the ore (leaching), whereupon basic precipitation removes aluminium ions from the mixture by precipitating it as the hydroxide. The remaining insoluble alkali metal carbonate is then precipitated selectively; the salt is then dissolved in hydrochloric acid to produce the chloride. The result is then left to evaporate and the alkali metal can then be isolated. Lithium and sodium are typically isolated through electrolysis from their liquid chlorides, with calcium chloride typically added to lower the melting point of the mixture. The heavier alkali metals, however, are more typically isolated in a different way, where a reducing agent (typically sodium for potassium and magnesium or calcium for the heaviest alkali metals) is used to reduce the alkali metal chloride. The liquid or gaseous product (the alkali metal) then undergoes fractional distillation for purification. Most routes to the pure alkali metals require the use of electrolysis due to their high reactivity; one of the few which does not is the pyrolysis of the corresponding alkali metal azide, which yields the metal for sodium, potassium, rubidium, and caesium and the nitride for lithium.
Lithium salts have to be extracted from the water of mineral springs, brine pools, and brine deposits. The metal is produced electrolytically from a mixture of fused lithium chloride and potassium chloride.
Sodium occurs mostly in seawater and dried seabed, but is now produced through electrolysis of sodium chloride by lowering the melting point of the substance to below 700 °C through the use of a Downs cell. Extremely pure sodium can be produced through the thermal decomposition of sodium azide. Potassium occurs in many minerals, such as sylvite (potassium chloride). Previously, potassium was generally made from the electrolysis of potassium chloride or potassium hydroxide, found extensively in places such as Canada, Russia, Belarus, Germany, Israel, United States, and Jordan, in a method similar to how sodium was produced in the late 1800s and early 1900s. It can also be produced from seawater. However, these methods are problematic because the potassium metal tends to dissolve in its molten chloride and vaporises significantly at the operating temperatures, potentially forming the explosive superoxide. As a result, pure potassium metal is now produced by reducing molten potassium chloride with sodium metal at 850 °C.
: Na (g) + KCl (l) `{{eqm}}`{=mediawiki} NaCl (l) + K (g)
Although sodium is less reactive than potassium, this process works because at such high temperatures potassium is more volatile than sodium and can easily be distilled off, so that the equilibrium shifts towards the right to produce more potassium gas and proceeds almost to completion.
Metals like sodium are obtained by electrolysis of molten salts. Rb & Cs obtained mainly as by products of Li processing. To make pure caesium, ores of caesium and rubidium are crushed and heated to 650 °C with sodium metal, generating an alloy that can then be separated via a fractional distillation technique. Because metallic caesium is too reactive to handle, it is normally offered as caesium azide (CsN3). Caesium hydroxide is formed when caesium interacts aggressively with water and ice (CsOH).
Rubidium is the 16th most abundant element in the earth\'s crust; however, it is quite rare. Some minerals found in North America, South Africa, Russia, and Canada contain rubidium. Some potassium minerals (lepidolites, biotites, feldspar, carnallite) contain it, together with caesium. Pollucite, carnallite, leucite, and lepidolite are all minerals that contain rubidium. As a by-product of lithium extraction, it is commercially obtained from lepidolite. Rubidium is also found in potassium rocks and brines, which is a commercial supply. The majority of rubidium is now obtained as a byproduct of refining lithium. Rubidium is used in vacuum tubes as a getter, a material that combines with and removes trace gases from vacuum tubes. For several years in the 1950s and 1960s, a by-product of the potassium production called Alkarb was a main source for rubidium. Alkarb contained 21% rubidium while the rest was potassium and a small fraction of caesium. Today the largest producers of caesium, for example the Tanco Mine in Manitoba, Canada, produce rubidium as by-product from pollucite. Today, a common method for separating rubidium from potassium and caesium is the fractional crystallisation of a rubidium and caesium alum (Cs, Rb)Al(SO~4~)~2~·12H~2~O, which yields pure rubidium alum after approximately 30 recrystallisations. The limited applications and the lack of a mineral rich in rubidium limit the production of rubidium compounds to 2 to 4 tonnes per year. Caesium, however, is not produced from the above reaction. Instead, the mining of pollucite ore is the main method of obtaining pure caesium, extracted from the ore mainly by three methods: acid digestion, alkaline decomposition, and direct reduction. Both metals are produced as by-products of lithium production: after 1958, when interest in lithium\'s thermonuclear properties increased sharply, the production of rubidium and caesium also increased correspondingly. Pure rubidium and caesium metals are produced by reducing their chlorides with calcium metal at 750 °C and low pressure.
As a result of its extreme rarity in nature, most francium is synthesised in the nuclear reaction ^197^Au + ^18^O → ^210^Fr + 5 n, yielding francium-209, francium-210, and francium-211. The greatest quantity of francium ever assembled to date is about 300,000 neutral atoms, which were synthesised using the nuclear reaction given above. When the only natural isotope francium-223 is specifically required, it is produced as the alpha daughter of actinium-227, itself produced synthetically from the neutron irradiation of natural radium-226, one of the daughters of natural uranium-238.
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| 20 |
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## Applications
Lithium, sodium, and potassium have many useful applications, while rubidium and caesium are very notable in academic contexts but do not have many applications yet. Lithium is the key ingredient for a range of lithium-based batteries, and lithium oxide can help process silica. Lithium stearate is a thickener and can be used to make lubricating greases; it is produced from lithium hydroxide, which is also used to absorb carbon dioxide in space capsules and submarines. Lithium chloride is used as a brazing alloy for aluminium parts. In medicine, some lithium salts are used as mood-stabilising pharmaceuticals. Metallic lithium is used in alloys with magnesium and aluminium to give very tough and light alloys.
Sodium compounds have many applications, the most well-known being sodium chloride as table salt. Sodium salts of fatty acids are used as soap. Pure sodium metal also has many applications, including use in sodium-vapour lamps, which produce very efficient light compared to other types of lighting, and can help smooth the surface of other metals. Being a strong reducing agent, it is often used to reduce many other metals, such as titanium and zirconium, from their chlorides. Furthermore, it is very useful as a heat-exchange liquid in fast breeder nuclear reactors due to its low melting point, viscosity, and cross-section towards neutron absorption. Sodium-ion batteries may provide cheaper alternatives to their equivalent lithium-based cells. Both sodium and potassium are commonly used as GRAS counterions to create more water-soluble and hence more bioavailable salt forms of acidic pharmaceuticals.
Potassium compounds are often used as fertilisers as potassium is an important element for plant nutrition. Potassium hydroxide is a very strong base, and is used to control the pH of various substances. Potassium nitrate and potassium permanganate are often used as powerful oxidising agents. Potassium superoxide is used in breathing masks, as it reacts with carbon dioxide to give potassium carbonate and oxygen gas. Pure potassium metal is not often used, but its alloys with sodium may substitute for pure sodium in fast breeder nuclear reactors.
Rubidium and caesium are often used in atomic clocks. Caesium atomic clocks are extraordinarily accurate; if a clock had been made at the time of the dinosaurs, it would be off by less than four seconds (after 80 million years). For that reason, caesium atoms are used as the definition of the second. Rubidium ions are often used in purple fireworks, and caesium is often used in drilling fluids in the petroleum industry.
Francium has no commercial applications, but because of francium\'s relatively simple atomic structure, among other things, it has been used in spectroscopy experiments, leading to more information regarding energy levels and the coupling constants of the weak interaction. Studies on the light emitted by laser-trapped francium-210 ions have provided accurate data on transitions between atomic energy levels, similar to those predicted by quantum theory.
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## Biological role and precautions {#biological_role_and_precautions}
### Metals
Pure alkali metals are dangerously reactive with air and water and must be kept away from heat, fire, oxidising agents, acids, most organic compounds, halocarbons, plastics, and moisture. They also react with carbon dioxide and carbon tetrachloride, so that normal fire extinguishers are counterproductive when used on alkali metal fires. Some Class D dry powder extinguishers designed for metal fires are effective, depriving the fire of oxygen and cooling the alkali metal.
Experiments are usually conducted using only small quantities of a few grams in a fume hood. Small quantities of lithium may be disposed of by reaction with cool water, but the heavier alkali metals should be dissolved in the less reactive isopropanol. The alkali metals must be stored under mineral oil or an inert atmosphere. The inert atmosphere used may be argon or nitrogen gas, except for lithium, which reacts with nitrogen. Rubidium and caesium must be kept away from air, even under oil, because even a small amount of air diffused into the oil may trigger formation of the dangerously explosive peroxide; for the same reason, potassium should not be stored under oil in an oxygen-containing atmosphere for longer than 6 months.
### Ions
The bioinorganic chemistry of the alkali metal ions has been extensively reviewed. Solid state crystal structures have been determined for many complexes of alkali metal ions in small peptides, nucleic acid constituents, carbohydrates and ionophore complexes.
Lithium naturally only occurs in traces in biological systems and has no known biological role, but does have effects on the body when ingested. Lithium carbonate is used as a mood stabiliser in psychiatry to treat bipolar disorder (manic-depression) in daily doses of about 0.5 to 2 grams, although there are side-effects. Excessive ingestion of lithium causes drowsiness, slurred speech and vomiting, among other symptoms, and poisons the central nervous system, which is dangerous as the required dosage of lithium to treat bipolar disorder is only slightly lower than the toxic dosage. Its biochemistry, the way it is handled by the human body and studies using rats and goats suggest that it is an essential trace element, although the natural biological function of lithium in humans has yet to be identified.
Sodium and potassium occur in all known biological systems, generally functioning as electrolytes inside and outside cells. Sodium is an essential nutrient that regulates blood volume, blood pressure, osmotic equilibrium and pH; the minimum physiological requirement for sodium is 500 milligrams per day. Sodium chloride (also known as common salt) is the principal source of sodium in the diet, and is used as seasoning and preservative, such as for pickling and jerky; most of it comes from processed foods. The Dietary Reference Intake for sodium is 1.5 grams per day, but most people in the United States consume more than 2.3 grams per day, the minimum amount that promotes hypertension; this in turn causes 7.6 million premature deaths worldwide.
Potassium is the major cation (positive ion) inside animal cells, while sodium is the major cation outside animal cells. The concentration differences of these charged particles causes a difference in electric potential between the inside and outside of cells, known as the membrane potential. The balance between potassium and sodium is maintained by ion transporter proteins in the cell membrane. The cell membrane potential created by potassium and sodium ions allows the cell to generate an action potential---a \"spike\" of electrical discharge. The ability of cells to produce electrical discharge is critical for body functions such as neurotransmission, muscle contraction, and heart function. Disruption of this balance may thus be fatal: for example, ingestion of large amounts of potassium compounds can lead to hyperkalemia strongly influencing the cardiovascular system. Potassium chloride is used in the United States for lethal injection executions.
Due to their similar atomic radii, rubidium and caesium in the body mimic potassium and are taken up similarly. Rubidium has no known biological role, but may help stimulate metabolism, and, similarly to caesium, replace potassium in the body causing potassium deficiency. Partial substitution is quite possible and rather non-toxic: a 70 kg person contains on average 0.36 g of rubidium, and an increase in this value by 50 to 100 times did not show negative effects in test persons. Rats can survive up to 50% substitution of potassium by rubidium. Rubidium (and to a much lesser extent caesium) can function as temporary cures for hypokalemia; while rubidium can adequately physiologically substitute potassium in some systems, caesium is never able to do so. There is only very limited evidence in the form of deficiency symptoms for rubidium being possibly essential in goats; even if this is true, the trace amounts usually present in food are more than enough.
Caesium compounds are rarely encountered by most people, but most caesium compounds are mildly toxic. Like rubidium, caesium tends to substitute potassium in the body, but is significantly larger and is therefore a poorer substitute. Excess caesium can lead to hypokalemia, arrhythmia, and acute cardiac arrest, but such amounts would not ordinarily be encountered in natural sources. As such, caesium is not a major chemical environmental pollutant. The median lethal dose (LD~50~) value for caesium chloride in mice is 2.3 g per kilogram, which is comparable to the LD~50~ values of potassium chloride and sodium chloride. Caesium chloride has been promoted as an alternative cancer therapy, but has been linked to the deaths of over 50 patients, on whom it was used as part of a scientifically unvalidated cancer treatment.
Radioisotopes of caesium require special precautions: the improper handling of caesium-137 gamma ray sources can lead to release of this radioisotope and radiation injuries. Perhaps the best-known case is the Goiânia accident of 1987, in which an improperly-disposed-of radiation therapy system from an abandoned clinic in the city of Goiânia, Brazil, was scavenged from a junkyard, and the glowing caesium salt sold to curious, uneducated buyers. This led to four deaths and serious injuries from radiation exposure. Together with caesium-134, iodine-131, and strontium-90, caesium-137 was among the isotopes distributed by the Chernobyl disaster which constitute the greatest risk to health. Radioisotopes of francium would presumably be dangerous as well due to their high decay energy and short half-life, but none have been produced in large enough amounts to pose any serious risk
| 1,052 |
Alkali metal
| 22 |
673 |
The **atomic number** or **nuclear charge number** (symbol ***Z***) of a chemical element is the charge number of its atomic nucleus. For ordinary nuclei composed of protons and neutrons, this is equal to the **proton number** (***n*~p~**) or the number of protons found in the nucleus of every atom of that element. The atomic number can be used to uniquely identify ordinary chemical elements. In an ordinary uncharged atom, the atomic number is also equal to the number of electrons.
For an ordinary atom which contains protons, neutrons and electrons, the sum of the atomic number *Z* and the neutron number *N* gives the atom\'s atomic mass number *A*. Since protons and neutrons have approximately the same mass (and the mass of the electrons is negligible for many purposes) and the mass defect of the nucleon binding is always small compared to the nucleon mass, the atomic mass of any atom, when expressed in daltons (making a quantity called the \"relative isotopic mass\"), is within 1% of the whole number *A*.
Atoms with the same atomic number but different neutron numbers, and hence different mass numbers, are known as isotopes. A little more than three-quarters of naturally occurring elements exist as a mixture of isotopes (see monoisotopic elements), and the average isotopic mass of an isotopic mixture for an element (called the relative atomic mass) in a defined environment on Earth determines the element\'s standard atomic weight. Historically, it was these atomic weights of elements (in comparison to hydrogen) that were the quantities measurable by chemists in the 19th century.
The conventional symbol *Z* comes from the German word *Zahl* \'number\', which, before the modern synthesis of ideas from chemistry and physics, merely denoted an element\'s numerical place in the periodic table, whose order was then approximately, but not completely, consistent with the order of the elements by atomic weights. Only after 1915, with the suggestion and evidence that this *Z* number was also the nuclear charge and a physical characteristic of atoms, did the word *Atomzahl* (and its English equivalent *atomic number*) come into common use in this context.
The rules above do not always apply to exotic atoms which contain short-lived elementary particles other than protons, neutrons and electrons.
## Notation
The atomic number is used in AZE notation, (with *A* as the mass number, *Z* the atomic number, and E for element) to denote an isotope. When a chemical symbol is used, e.g. \"C\" for carbon, standard notation uses a superscript at the upper left of the chemical symbol for the mass number and indicates the atomic number with a subscript at the lower left (e.g. `{{nuclide|He|3}}`{=mediawiki}, `{{nuclide|He|4}}`{=mediawiki}, `{{nuclide|C|12}}`{=mediawiki}, `{{nuclide|C|14}}`{=mediawiki}, `{{nuclide|U|235}}`{=mediawiki}, and `{{nuclide|U|239}}`{=mediawiki}). Because the atomic number is given by the element symbol, it is common to state only the mass number in the superscript and leave out the atomic number subscript (e.g. `{{SimpleNuclide|He|3}}`{=mediawiki}, `{{SimpleNuclide|He|4}}`{=mediawiki}, `{{SimpleNuclide|C|12}}`{=mediawiki}, `{{SimpleNuclide|C|14}}`{=mediawiki}, `{{SimpleNuclide|U|235}}`{=mediawiki}, and `{{SimpleNuclide|U|239}}`{=mediawiki}).
The common pronunciation of the AZE notation is different from how it is written: `{{nuclide|He|4}}`{=mediawiki} is commonly pronounced as helium-four instead of four-two-helium, and `{{nuclide|U|235}}`{=mediawiki} as uranium two-thirty-five (American English) or uranium-two-three-five (British) instead of 235-92-uranium. Various notations appear in older sources were used, such as Ne(22) in 1934, Ne^22^ for neon-22 (1935) or Pb~210~ for lead-210 (1933)
| 541 |
Atomic number
| 0 |
673 |
## History
In the 19th century, the term \"atomic number\" typically meant the number of atoms in a given volume. Modern chemists prefer to use the concept of molar concentration.
In 1913, Antonius van den Broek proposed that the electric charge of an atomic nucleus, expressed as a multiplier of the elementary charge, was equal to the element\'s sequential position on the periodic table. Ernest Rutherford, in various articles in which he discussed van den Broek\'s idea, used the term \"atomic number\" to refer to an element\'s position on the periodic table. No writer before Rutherford is known to have used the term \"atomic number\" in this way, so it was probably he who established this definition.
After Rutherford deduced the existence of the proton in 1920, \"atomic number\" customarily referred to the proton number of an atom. In 1921, the German Atomic Weight Commission based its new periodic table on the nuclear charge number and in 1923 the International Committee on Chemical Elements followed suit.
### The periodic table and a natural number for each element {#the_periodic_table_and_a_natural_number_for_each_element}
The periodic table of elements creates an ordering of the elements, and so they can be numbered in order. Dmitri Mendeleev arranged his first periodic tables (first published on March 6, 1869) in order of atomic weight (\"Atomgewicht\"). However, in consideration of the elements\' observed chemical properties, he changed the order slightly and placed tellurium (atomic weight 127.6) ahead of iodine (atomic weight 126.9). This placement is consistent with the modern practice of ordering the elements by proton number, *Z*, but that number was not known or suspected at the time.
A simple numbering based on atomic weight position was never entirely satisfactory. In addition to the case of iodine and tellurium, several other pairs of elements (such as argon and potassium, cobalt and nickel) were later shown to have nearly identical or reversed atomic weights, thus requiring their placement in the periodic table to be determined by their chemical properties. However the gradual identification of more and more chemically similar lanthanide elements, whose atomic number was not obvious, led to inconsistency and uncertainty in the periodic numbering of elements at least from lutetium (element 71) onward (hafnium was not known at this time).
### The Rutherford-Bohr model and van den Broek {#the_rutherford_bohr_model_and_van_den_broek}
In 1911, Ernest Rutherford gave a model of the atom in which a central nucleus held most of the atom\'s mass and a positive charge which, in units of the electron\'s charge, was to be approximately equal to half of the atom\'s atomic weight, expressed in numbers of hydrogen atoms. This central charge would thus be approximately half the atomic weight (though it was almost 25% different from the atomic number of gold `{{nowrap|1=(''Z'' = 79}}`{=mediawiki}, `{{nowrap|1=''A'' = 197}}`{=mediawiki}), the single element from which Rutherford made his guess). Nevertheless, in spite of Rutherford\'s estimation that gold had a central charge of about 100 (but was element `{{nowrap|1=''Z'' = 79}}`{=mediawiki} on the periodic table), a month after Rutherford\'s paper appeared, Antonius van den Broek first formally suggested that the central charge and number of electrons in an atom were *exactly* equal to its place in the periodic table (also known as element number, atomic number, and symbolized *Z*). This eventually proved to be the case.
### Moseley\'s 1913 experiment {#moseleys_1913_experiment}
The experimental position improved dramatically after research by Henry Moseley in 1913. Moseley, after discussions with Bohr who was at the same lab (and who had used Van den Broek\'s hypothesis in his Bohr model of the atom), decided to test Van den Broek\'s and Bohr\'s hypothesis directly, by seeing if spectral lines emitted from excited atoms fitted the Bohr theory\'s postulation that the frequency of the spectral lines be proportional to the square of *Z*.
To do this, Moseley measured the wavelengths of the innermost photon transitions (K and L lines) produced by the elements from aluminium (*Z* = 13) to gold (*Z* = 79) used as a series of movable anodic targets inside an x-ray tube. The square root of the frequency of these photons `{{nowrap|(x-rays)}}`{=mediawiki} increased from one target to the next in an arithmetic progression. This led to the conclusion (Moseley\'s law) that the atomic number does closely correspond (with an offset of one unit for K-lines, in Moseley\'s work) to the calculated electric charge of the nucleus, i.e. the element number *Z*. Among other things, Moseley demonstrated that the lanthanide series (from lanthanum to lutetium inclusive) must have 15 members---no fewer and no more---which was far from obvious from known chemistry at that time.
### Missing elements {#missing_elements}
After Moseley\'s death in 1915, the atomic numbers of all known elements from hydrogen to uranium (*Z* = 92) were examined by his method. There were seven elements (with *Z* \< 92) which were not found and therefore identified as still undiscovered, corresponding to atomic numbers 43, 61, 72, 75, 85, 87 and 91. From 1918 to 1947, all seven of these missing elements were discovered. By this time, the first four transuranium elements had also been discovered, so that the periodic table was complete with no gaps as far as curium (*Z* = 96).
| 858 |
Atomic number
| 1 |
673 |
## History
### The proton and the idea of nuclear electrons {#the_proton_and_the_idea_of_nuclear_electrons}
In 1915, the reason for nuclear charge being quantized in units of *Z*, which were now recognized to be the same as the element number, was not understood. An old idea called Prout\'s hypothesis had postulated that the elements were all made of residues (or \"protyles\") of the lightest element hydrogen, which in the Bohr-Rutherford model had a single electron and a nuclear charge of one. However, as early as 1907, Rutherford and Thomas Royds had shown that alpha particles, which had a charge of +2, were the nuclei of helium atoms, which had a mass four times that of hydrogen, not two times. If Prout\'s hypothesis were true, something had to be neutralizing some of the charge of the hydrogen nuclei present in the nuclei of heavier atoms.
In 1917, Rutherford succeeded in generating hydrogen nuclei from a nuclear reaction between alpha particles and nitrogen gas, and believed he had proven Prout\'s law. He called the new heavy nuclear particles protons in 1920 (alternate names being proutons and protyles). It had been immediately apparent from the work of Moseley that the nuclei of heavy atoms have more than twice as much mass as would be expected from their being made of hydrogen nuclei, and thus there was required a hypothesis for the neutralization of the extra protons presumed present in all heavy nuclei. A helium nucleus was presumed to have four protons plus two \"nuclear electrons\" (electrons bound inside the nucleus) to cancel two charges. At the other end of the periodic table, a nucleus of gold with a mass 197 times that of hydrogen was thought to contain 118 nuclear electrons in the nucleus to give it a residual charge of +79, consistent with its atomic number.
### Discovery of the neutron makes *Z* the proton number {#discovery_of_the_neutron_makes_z_the_proton_number}
All consideration of nuclear electrons ended with James Chadwick\'s discovery of the neutron in 1932. An atom of gold now was seen as containing 118 neutrons rather than 118 nuclear electrons, and its positive nuclear charge now was realized to come entirely from a content of 79 protons. Since Moseley had previously shown that the atomic number *Z* of an element equals this positive charge, it was now clear that *Z* is identical to the number of protons of its nuclei.
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## Chemical properties {#chemical_properties}
Each element has a specific set of chemical properties as a consequence of the number of electrons present in the neutral atom, which is *Z* (the atomic number). The configuration of these electrons follows from the principles of quantum mechanics. The number of electrons in each element\'s electron shells, particularly the outermost valence shell, is the primary factor in determining its chemical bonding behavior. Hence, it is the atomic number alone that determines the chemical properties of an element; and it is for this reason that an element can be defined as consisting of *any* mixture of atoms with a given atomic number.
## New elements {#new_elements}
The quest for new elements is usually described using atomic numbers. As of `{{year}}`{=mediawiki}, all elements with atomic numbers 1 to 118 have been observed. The most recent element discovered was number 117 (tennessine) in 2009. Synthesis of new elements is accomplished by bombarding target atoms of heavy elements with ions, such that the sum of the atomic numbers of the target and ion elements equals the atomic number of the element being created. In general, the half-life of a nuclide becomes shorter as atomic number increases, though undiscovered nuclides with certain \"magic\" numbers of protons and neutrons may have relatively longer half-lives and comprise an island of stability.
A hypothetical element composed only of neutrons, neutronium, has also been proposed and would have atomic number 0, but has never been observed
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*Volume 5: Anatomic*}} `{{for-multi|the anatomy of plants|Plant anatomy|other uses}}`{=mediawiki} `{{good article}}`{=mediawiki} `{{Use dmy dates|date=July 2022}}`{=mediawiki} `{{Use Oxford spelling|date=September 2016}}`{=mediawiki} `{{TopicTOC-Biology}}`{=mediawiki} **Anatomy** (`{{etymology|grc|''{{wikt-lang|grc|ἀνατομή}}'' ({{grc-transl|ἀνατομή}})|[[dissection]]}}`{=mediawiki}) is the branch of morphology concerned with the study of the internal structure of organisms and their parts. Anatomy is a branch of natural science that deals with the structural organization of living things. It is an old science, having its beginnings in prehistoric times. Anatomy is inherently tied to developmental biology, embryology, comparative anatomy, evolutionary biology, and phylogeny, as these are the processes by which anatomy is generated, both over immediate and long-term timescales. Anatomy and physiology, which study the structure and function of organisms and their parts respectively, make a natural pair of related disciplines, and are often studied together. Human anatomy is one of the essential basic sciences that are applied in medicine, and is often studied alongside physiology.
Anatomy is a complex and dynamic field that is constantly evolving as discoveries are made. In recent years, there has been a significant increase in the use of advanced imaging techniques, such as MRI and CT scans, which allow for more detailed and accurate visualizations of the body\'s structures.
The discipline of anatomy is divided into macroscopic and microscopic parts. Macroscopic anatomy, or gross anatomy, is the examination of an animal\'s body parts using unaided eyesight. Gross anatomy also includes the branch of superficial anatomy. Microscopic anatomy involves the use of optical instruments in the study of the tissues of various structures, known as histology, and also in the study of cells.
The history of anatomy is characterized by a progressive understanding of the functions of the organs and structures of the human body. Methods have also improved dramatically, advancing from the examination of animals by dissection of carcasses and cadavers (corpses) to 20th-century medical imaging techniques, including X-ray, ultrasound, and magnetic resonance imaging.
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## Etymology and definition {#etymology_and_definition}
Derived from the Greek *ἀνατομή* *anatomē* \"dissection\" (from *ἀνατέμνω* *anatémnō* \"I cut up, cut open\" from ἀνά *aná* \"up\", and τέμνω *témnō* \"I cut\"), anatomy is the scientific study of the structure of organisms including their systems, organs and tissues. It includes the appearance and position of the various parts, the materials from which they are composed, and their relationships with other parts. Anatomy is quite distinct from physiology and biochemistry, which deal respectively with the functions of those parts and the chemical processes involved. For example, an anatomist is concerned with the shape, size, position, structure, blood supply and innervation of an organ such as the liver; while a physiologist is interested in the production of bile, the role of the liver in nutrition and the regulation of bodily functions.
The discipline of anatomy can be subdivided into a number of branches, including gross or macroscopic anatomy and microscopic anatomy. Gross anatomy is the study of structures large enough to be seen with the naked eye, and also includes superficial anatomy or surface anatomy, the study by sight of the external body features. Microscopic anatomy is the study of structures on a microscopic scale, along with histology (the study of tissues), and embryology (the study of an organism in its immature condition). Regional anatomy is the study of the interrelationships of all of the structures in a specific body region, such as the abdomen. In contrast, systemic anatomy is the study of the structures that make up a discrete body system---that is, a group of structures that work together to perform a unique body function, such as the digestive system.
Anatomy can be studied using both invasive and non-invasive methods with the goal of obtaining information about the structure and organization of organs and systems. Methods used include dissection, in which a body is opened and its organs studied, and endoscopy, in which a video camera-equipped instrument is inserted through a small incision in the body wall and used to explore the internal organs and other structures. Angiography using X-rays or magnetic resonance angiography are methods to visualize blood vessels.
The term \"anatomy\" is commonly taken to refer to human anatomy. However, substantially similar structures and tissues are found throughout the rest of the animal kingdom, and the term also includes the anatomy of other animals. The term *zootomy* is also sometimes used to specifically refer to non-human animals. The structure and tissues of plants are of a dissimilar nature and they are studied in plant anatomy.
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## Animal tissues {#animal_tissues}
The kingdom Animalia contains multicellular organisms that are heterotrophic and motile (although some have secondarily adopted a sessile lifestyle). Most animals have bodies differentiated into separate tissues and these animals are also known as eumetazoans. They have an internal digestive chamber, with one or two openings; the gametes are produced in multicellular sex organs, and the zygotes include a blastula stage in their embryonic development. Metazoans do not include the sponges, which have undifferentiated cells.
Unlike plant cells, animal cells have neither a cell wall nor chloroplasts. Vacuoles, when present, are more in number and much smaller than those in the plant cell. The body tissues are composed of numerous types of cells, including those found in muscles, nerves and skin. Each typically has a cell membrane formed of phospholipids, cytoplasm and a nucleus. All of the different cells of an animal are derived from the embryonic germ layers. Those simpler invertebrates which are formed from two germ layers of ectoderm and endoderm are called diploblastic and the more developed animals whose structures and organs are formed from three germ layers are called triploblastic. All of a triploblastic animal\'s tissues and organs are derived from the three germ layers of the embryo, the ectoderm, mesoderm and endoderm.
Animal tissues can be grouped into four basic types: connective, epithelial, muscle and nervous tissue.
### Connective tissue {#connective_tissue}
Connective tissues are fibrous and made up of cells scattered among inorganic material called the extracellular matrix. Often called fascia (from the Latin \"fascia,\" meaning \"band\" or \"bandage\"), connective tissues give shape to organs and holds them in place. The main types are loose connective tissue, adipose tissue, fibrous connective tissue, cartilage and bone. The extracellular matrix contains proteins, the chief and most abundant of which is collagen. Collagen plays a major part in organizing and maintaining tissues. The matrix can be modified to form a skeleton to support or protect the body. An exoskeleton is a thickened, rigid cuticle which is stiffened by mineralization, as in crustaceans or by the cross-linking of its proteins as in insects. An endoskeleton is internal and present in all developed animals, as well as in many of those less developed.
### Epithelium
Epithelial tissue is composed of closely packed cells, bound to each other by cell adhesion molecules, with little intercellular space. Epithelial cells can be squamous (flat), cuboidal or columnar and rest on a basal lamina, the upper layer of the basement membrane, the lower layer is the reticular lamina lying next to the connective tissue in the extracellular matrix secreted by the epithelial cells. There are many different types of epithelium, modified to suit a particular function. In the respiratory tract there is a type of ciliated epithelial lining; in the small intestine there are microvilli on the epithelial lining and in the large intestine there are intestinal villi. Skin consists of an outer layer of keratinized stratified squamous epithelium that covers the exterior of the vertebrate body. Keratinocytes make up to 95% of the cells in the skin. The epithelial cells on the external surface of the body typically secrete an extracellular matrix in the form of a cuticle. In simple animals this may just be a coat of glycoproteins. In more advanced animals, many glands are formed of epithelial cells.
### Muscle tissue {#muscle_tissue}
Muscle cells (myocytes) form the active contractile tissue of the body. Muscle tissue functions to produce force and cause motion, either locomotion or movement within internal organs. Muscle is formed of contractile filaments and is separated into three main types; smooth muscle, skeletal muscle and cardiac muscle. Smooth muscle has no striations when examined microscopically. It contracts slowly but maintains contractibility over a wide range of stretch lengths. It is found in such organs as sea anemone tentacles and the body wall of sea cucumbers. Skeletal muscle contracts rapidly but has a limited range of extension. It is found in the movement of appendages and jaws. Obliquely striated muscle is intermediate between the other two. The filaments are staggered and this is the type of muscle found in earthworms that can extend slowly or make rapid contractions. In higher animals striated muscles occur in bundles attached to bone to provide movement and are often arranged in antagonistic sets. Smooth muscle is found in the walls of the uterus, bladder, intestines, stomach, oesophagus, respiratory airways, and blood vessels. Cardiac muscle is found only in the heart, allowing it to contract and pump blood round the body.
### Nervous tissue {#nervous_tissue}
Nervous tissue is composed of many nerve cells known as neurons which transmit information. In some slow-moving radially symmetrical marine animals such as ctenophores and cnidarians (including sea anemones and jellyfish), the nerves form a nerve net, but in most animals they are organized longitudinally into bundles. In simple animals, receptor neurons in the body wall cause a local reaction to a stimulus. In more complex animals, specialized receptor cells such as chemoreceptors and photoreceptors are found in groups and send messages along neural networks to other parts of the organism. Neurons can be connected together in ganglia. In higher animals, specialized receptors are the basis of sense organs and there is a central nervous system (brain and spinal cord) and a peripheral nervous system. The latter consists of sensory nerves that transmit information from sense organs and motor nerves that influence target organs. The peripheral nervous system is divided into the somatic nervous system which conveys sensation and controls voluntary muscle, and the autonomic nervous system which involuntarily controls smooth muscle, certain glands and internal organs, including the stomach.
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## Vertebrate anatomy {#vertebrate_anatomy}
All vertebrates have a similar basic body plan and at some point in their lives, mostly in the embryonic stage, share the major chordate characteristics: a stiffening rod, the notochord; a dorsal hollow tube of nervous material, the neural tube; pharyngeal arches; and a tail posterior to the anus. The spinal cord is protected by the vertebral column and is above the notochord, and the gastrointestinal tract is below it. Nervous tissue is derived from the ectoderm, connective tissues are derived from mesoderm, and gut is derived from the endoderm. At the posterior end is a tail which continues the spinal cord and vertebrae but not the gut. The mouth is found at the anterior end of the animal, and the anus at the base of the tail. The defining characteristic of a vertebrate is the vertebral column, formed in the development of the segmented series of vertebrae. In most vertebrates the notochord becomes the nucleus pulposus of the intervertebral discs. However, a few vertebrates, such as the sturgeon and the coelacanth, retain the notochord into adulthood. Jawed vertebrates are typified by paired appendages, fins or legs, which may be secondarily lost. The limbs of vertebrates are considered to be homologous because the same underlying skeletal structure was inherited from their last common ancestor. This is one of the arguments put forward by Charles Darwin to support his theory of evolution.
### Fish anatomy {#fish_anatomy}
The body of a fish is divided into a head, trunk and tail, although the divisions between the three are not always externally visible. The skeleton, which forms the support structure inside the fish, is either made of cartilage, in cartilaginous fish, or bone in bony fish. The main skeletal element is the vertebral column, composed of articulating vertebrae which are lightweight yet strong. The ribs attach to the spine and there are no limbs or limb girdles. The main external features of the fish, the fins, are composed of either bony or soft spines called rays, which with the exception of the caudal fins, have no direct connection with the spine. They are supported by the muscles which compose the main part of the trunk. The heart has two chambers and pumps the blood through the respiratory surfaces of the gills and on round the body in a single circulatory loop. The eyes are adapted for seeing underwater and have only local vision. There is an inner ear but no external or middle ear. Low frequency vibrations are detected by the lateral line system of sense organs that run along the length of the sides of fish, and these respond to nearby movements and to changes in water pressure.
Sharks and rays are basal fish with numerous primitive anatomical features similar to those of ancient fish, including skeletons composed of cartilage. Their bodies tend to be dorso-ventrally flattened, they usually have five pairs of gill slits and a large mouth set on the underside of the head. The dermis is covered with separate dermal placoid scales. They have a cloaca into which the urinary and genital passages open, but not a swim bladder. Cartilaginous fish produce a small number of large, yolky eggs. Some species are ovoviviparous and the young develop internally but others are oviparous and the larvae develop externally in egg cases.
The bony fish lineage shows more derived anatomical traits, often with major evolutionary changes from the features of ancient fish. They have a bony skeleton, are generally laterally flattened, have five pairs of gills protected by an operculum, and a mouth at or near the tip of the snout. The dermis is covered with overlapping scales. Bony fish have a swim bladder which helps them maintain a constant depth in the water column, but not a cloaca. They mostly spawn a large number of small eggs with little yolk which they broadcast into the water column.
### Amphibian anatomy {#amphibian_anatomy}
Amphibians are a class of animals comprising frogs, salamanders and caecilians. They are tetrapods, but the caecilians and a few species of salamander have either no limbs or their limbs are much reduced in size. Their main bones are hollow and lightweight and are fully ossified and the vertebrae interlock with each other and have articular processes. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, but contains many mucous glands and in some species, poison glands. The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Amphibians breathe by means of buccal pumping, a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin which needs to be kept moist.
In frogs the pelvic girdle is robust and the hind legs are much longer and stronger than the forelimbs. The feet have four or five digits and the toes are often webbed for swimming or have suction pads for climbing. Frogs have large eyes and no tail. Salamanders resemble lizards in appearance; their short legs project sideways, the belly is close to or in contact with the ground and they have a long tail. Caecilians superficially resemble earthworms and are limbless. They burrow by means of zones of muscle contractions which move along the body and they swim by undulating their body from side to side.
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## Vertebrate anatomy {#vertebrate_anatomy}
### Reptile anatomy {#reptile_anatomy}
Reptiles are a class of animals comprising turtles, tuataras, lizards, snakes and crocodiles. They are tetrapods, but the snakes and a few species of lizard either have no limbs or their limbs are much reduced in size. Their bones are better ossified and their skeletons stronger than those of amphibians. The teeth are conical and mostly uniform in size. The surface cells of the epidermis are modified into horny scales which create a waterproof layer. Reptiles are unable to use their skin for respiration as do amphibians and have a more efficient respiratory system drawing air into their lungs by expanding their chest walls. The heart resembles that of the amphibian but there is a septum which more completely separates the oxygenated and deoxygenated bloodstreams. The reproductive system has evolved for internal fertilization, with a copulatory organ present in most species. The eggs are surrounded by amniotic membranes which prevents them from drying out and are laid on land, or develop internally in some species. The bladder is small as nitrogenous waste is excreted as uric acid.
Turtles are notable for their protective shells. They have an inflexible trunk encased in a horny carapace above and a plastron below. These are formed from bony plates embedded in the dermis which are overlain by horny ones and are partially fused with the ribs and spine. The neck is long and flexible and the head and the legs can be drawn back inside the shell. Turtles are vegetarians and the typical reptile teeth have been replaced by sharp, horny plates. In aquatic species, the front legs are modified into flippers.
**Tuataras** superficially resemble lizards but the lineages diverged in the Triassic period. There is one living species, *Sphenodon punctatus*. The skull has two openings (fenestrae) on either side and the jaw is rigidly attached to the skull. There is one row of teeth in the lower jaw and this fits between the two rows in the upper jaw when the animal chews. The teeth are merely projections of bony material from the jaw and eventually wear down. The brain and heart are more primitive than those of other reptiles, and the lungs have a single chamber and lack bronchi. The tuatara has a well-developed parietal eye on its forehead.
Lizards have skulls with only one fenestra on each side, the lower bar of bone below the second fenestra having been lost. This results in the jaws being less rigidly attached which allows the mouth to open wider. Lizards are mostly quadrupeds, with the trunk held off the ground by short, sideways-facing legs, but a few species have no limbs and resemble snakes. Lizards have moveable eyelids, eardrums are present and some species have a central parietal eye.
Snakes are closely related to lizards, having branched off from a common ancestral lineage during the Cretaceous period, and they share many of the same features. The skeleton consists of a skull, a hyoid bone, spine and ribs though a few species retain a vestige of the pelvis and rear limbs in the form of pelvic spurs. The bar under the second fenestra has also been lost and the jaws have extreme flexibility allowing the snake to swallow its prey whole. Snakes lack moveable eyelids, the eyes being covered by transparent \"spectacle\" scales. They do not have eardrums but can detect ground vibrations through the bones of their skull. Their forked tongues are used as organs of taste and smell and some species have sensory pits on their heads enabling them to locate warm-blooded prey.
Crocodilians are large, low-slung aquatic reptiles with long snouts and large numbers of teeth. The head and trunk are dorso-ventrally flattened and the tail is laterally compressed. It undulates from side to side to force the animal through the water when swimming. The tough keratinized scales provide body armour and some are fused to the skull. The nostrils, eyes and ears are elevated above the top of the flat head enabling them to remain above the surface of the water when the animal is floating. Valves seal the nostrils and ears when it is submerged. Unlike other reptiles, crocodilians have hearts with four chambers allowing complete separation of oxygenated and deoxygenated blood.
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## Vertebrate anatomy {#vertebrate_anatomy}
### Bird anatomy {#bird_anatomy}
Birds are tetrapods but though their hind limbs are used for walking or hopping, their front limbs are wings covered with feathers and adapted for flight. Birds are endothermic, have a high metabolic rate, a light skeletal system and powerful muscles. The long bones are thin, hollow and very light. Air sac extensions from the lungs occupy the centre of some bones. The sternum is wide and usually has a keel and the caudal vertebrae are fused. There are no teeth and the narrow jaws are adapted into a horn-covered beak. The eyes are relatively large, particularly in nocturnal species such as owls. They face forwards in predators and sideways in ducks.
The feathers are outgrowths of the epidermis and are found in localized bands from where they fan out over the skin. Large flight feathers are found on the wings and tail, contour feathers cover the bird\'s surface and fine down occurs on young birds and under the contour feathers of water birds. The only cutaneous gland is the single uropygial gland near the base of the tail. This produces an oily secretion that waterproofs the feathers when the bird preens. There are scales on the legs, feet and claws on the tips of the toes.
### Mammal anatomy {#mammal_anatomy}
Mammals are a diverse class of animals, mostly terrestrial but some are aquatic and others have evolved flapping or gliding flight. They mostly have four limbs, but some aquatic mammals have no limbs or limbs modified into fins, and the forelimbs of bats are modified into wings. The legs of most mammals are situated below the trunk, which is held well clear of the ground. The bones of mammals are well ossified and their teeth, which are usually differentiated, are coated in a layer of prismatic enamel. The teeth are shed once (milk teeth) during the animal\'s lifetime or not at all, as is the case in cetaceans. Mammals have three bones in the middle ear and a cochlea in the inner ear. They are clothed in hair and their skin contains glands which secrete sweat. Some of these glands are specialized as mammary glands, producing milk to feed the young. Mammals breathe with lungs and have a muscular diaphragm separating the thorax from the abdomen which helps them draw air into the lungs. The mammalian heart has four chambers, and oxygenated and deoxygenated blood are kept entirely separate. Nitrogenous waste is excreted primarily as urea.
Mammals are amniotes, and most are viviparous, giving birth to live young. Exceptions to this are the egg-laying monotremes, the platypus and the echidnas of Australia. Most other mammals have a placenta through which the developing foetus obtains nourishment, but in marsupials, the foetal stage is very short and the immature young is born and finds its way to its mother\'s pouch where it latches on to a teat and completes its development.
#### Human anatomy {#human_anatomy}
Humans have the overall body plan of a mammal. Humans have a head, neck, trunk (which includes the thorax and abdomen), two arms and hands, and two legs and feet.
Generally, students of certain biological sciences, paramedics, prosthetists and orthotists, physiotherapists, occupational therapists, nurses, podiatrists, and medical students learn gross anatomy and microscopic anatomy from anatomical models, skeletons, textbooks, diagrams, photographs, lectures and tutorials and in addition, medical students generally also learn gross anatomy through practical experience of dissection and inspection of cadavers. The study of microscopic anatomy (or histology) can be aided by practical experience examining histological preparations (or slides) under a microscope.
Human anatomy, physiology and biochemistry are complementary basic medical sciences, which are generally taught to medical students in their first year at medical school. Human anatomy can be taught regionally or systemically; that is, respectively, studying anatomy by bodily regions such as the head and chest, or studying by specific systems, such as the nervous or respiratory systems. The major anatomy textbook, Gray\'s Anatomy, has been reorganized from a systems format to a regional format, in line with modern teaching methods. A thorough working knowledge of anatomy is required by physicians, especially surgeons and doctors working in some diagnostic specialties, such as histopathology and radiology.
Academic anatomists are usually employed by universities, medical schools or teaching hospitals. They are often involved in teaching anatomy, and research into certain systems, organs, tissues or cells.
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## Invertebrate anatomy {#invertebrate_anatomy}
Invertebrates constitute a vast array of living organisms ranging from the simplest unicellular eukaryotes such as *Paramecium* to such complex multicellular animals as the octopus, lobster and dragonfly. They constitute about 95% of the animal species. By definition, none of these creatures has a backbone. The cells of single-cell protozoans have the same basic structure as those of multicellular animals but some parts are specialized into the equivalent of tissues and organs. Locomotion is often provided by cilia or flagella or may proceed via the advance of pseudopodia, food may be gathered by phagocytosis, energy needs may be supplied by photosynthesis and the cell may be supported by an endoskeleton or an exoskeleton. Some protozoans can form multicellular colonies.
Metazoans are a multicellular organism, with different groups of cells serving different functions. The most basic types of metazoan tissues are epithelium and connective tissue, both of which are present in nearly all invertebrates. The outer surface of the epidermis is normally formed of epithelial cells and secretes an extracellular matrix which provides support to the organism. An endoskeleton derived from the mesoderm is present in echinoderms, sponges and some cephalopods. Exoskeletons are derived from the epidermis and is composed of chitin in arthropods (insects, spiders, ticks, shrimps, crabs, lobsters). Calcium carbonate constitutes the shells of molluscs, brachiopods and some tube-building polychaete worms and silica forms the exoskeleton of the microscopic diatoms and radiolaria. Other invertebrates may have no rigid structures but the epidermis may secrete a variety of surface coatings such as the pinacoderm of sponges, the gelatinous cuticle of cnidarians (polyps, sea anemones, jellyfish) and the collagenous cuticle of annelids. The outer epithelial layer may include cells of several types including sensory cells, gland cells and stinging cells. There may also be protrusions such as microvilli, cilia, bristles, spines and tubercles.
Marcello Malpighi, the father of microscopical anatomy, discovered that plants had tubules similar to those he saw in insects like the silk worm. He observed that when a ring-like portion of bark was removed on a trunk a swelling occurred in the tissues above the ring, and he unmistakably interpreted this as growth stimulated by food coming down from the leaves, and being captured above the ring.
### Arthropod anatomy {#arthropod_anatomy}
Arthropods comprise the largest phylum of invertebrates in the animal kingdom with over a million known species.
Insects possess segmented bodies supported by a hard-jointed outer covering, the exoskeleton, made mostly of chitin. The segments of the body are organized into three distinct parts, a head, a thorax and an abdomen. The head typically bears a pair of sensory antennae, a pair of compound eyes, one to three simple eyes (ocelli) and three sets of modified appendages that form the mouthparts. The thorax has three pairs of segmented legs, one pair each for the three segments that compose the thorax and one or two pairs of wings. The abdomen is composed of eleven segments, some of which may be fused and houses the digestive, respiratory, excretory and reproductive systems. There is considerable variation between species and many adaptations to the body parts, especially wings, legs, antennae and mouthparts.
Spiders a class of arachnids have four pairs of legs; a body of two segments---a cephalothorax and an abdomen. Spiders have no wings and no antennae. They have mouthparts called chelicerae which are often connected to venom glands as most spiders are venomous. They have a second pair of appendages called pedipalps attached to the cephalothorax. These have similar segmentation to the legs and function as taste and smell organs. At the end of each male pedipalp is a spoon-shaped cymbium that acts to support the copulatory organ.
## Other branches of anatomy {#other_branches_of_anatomy}
- Surface anatomy is important as the study of anatomical landmarks that can be readily seen from the exterior contours of the body. It enables medics and veterinarians to gauge the position and anatomy of the associated deeper structures. Superficial is a directional term that indicates that structures are located relatively close to the surface of the body.
- Comparative anatomy relates to the comparison of anatomical structures (both gross and microscopic) in different animals.
- Artistic anatomy relates to anatomic studies of body proportions for artistic reasons.
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## History
### Ancient
thumb\|upright=1.05\|Image of early rendition of anatomy findings
In 1600 BCE, the Edwin Smith Papyrus, an Ancient Egyptian medical text, described the heart and its vessels, as well as the brain and its meninges and cerebrospinal fluid, and the liver, spleen, kidneys, uterus and bladder. It showed the blood vessels diverging from the heart. The Ebers Papyrus (c. 1550 BCE) features a \"treatise on the heart\", with vessels carrying all the body\'s fluids to or from every member of the body.
Ancient Greek anatomy and physiology underwent great changes and advances throughout the early medieval world. Over time, this medical practice expanded due to a continually developing understanding of the functions of organs and structures in the body. Phenomenal anatomical observations of the human body were made, which contributed to the understanding of the brain, eye, liver, reproductive organs, and nervous system.
The Hellenistic Egyptian city of Alexandria was the stepping-stone for Greek anatomy and physiology. Alexandria not only housed the biggest library for medical records and books of the liberal arts in the world during the time of the Greeks but was also home to many medical practitioners and philosophers. Great patronage of the arts and sciences from the Ptolemaic dynasty of Egypt helped raise Alexandria up, further rivalling other Greek states\' cultural and scientific achievements.
Some of the most striking advances in early anatomy and physiology took place in Hellenistic Alexandria. Two of the most famous anatomists and physiologists of the third century were Herophilus and Erasistratus. These two physicians helped pioneer human dissection for medical research, using the cadavers of condemned criminals, which was considered taboo until the Renaissance---Herophilus was recognized as the first person to perform systematic dissections. Herophilus became known for his anatomical works, making impressive contributions to many branches of anatomy and many other aspects of medicine. Some of the works included classifying the system of the pulse, the discovery that human arteries had thicker walls than veins, and that the atria were parts of the heart. Herophilus\'s knowledge of the human body has provided vital input towards understanding the brain, eye, liver, reproductive organs, and nervous system and characterizing the course of the disease. Erasistratus accurately described the structure of the brain, including the cavities and membranes, and made a distinction between its cerebrum and cerebellum During his study in Alexandria, Erasistratus was particularly concerned with studies of the circulatory and nervous systems. He could distinguish the human body\'s sensory and motor nerves and believed air entered the lungs and heart, which was then carried throughout the body. His distinction between the arteries and veins---the arteries carrying the air through the body, while the veins carry the blood from the heart was a great anatomical discovery. Erasistratus was also responsible for naming and describing the function of the epiglottis and the heart\'s valves, including the tricuspid. During the third century, Greek physicians were able to differentiate nerves from blood vessels and tendons and to realize that the nerves convey neural impulses. It was Herophilus who made the point that damage to motor nerves induced paralysis. Herophilus named the meninges and ventricles in the brain, appreciated the division between cerebellum and cerebrum and recognized that the brain was the \"seat of intellect\" and not a \"cooling chamber\" as propounded by Aristotle Herophilus is also credited with describing the optic, oculomotor, motor division of the trigeminal, facial, vestibulocochlear and hypoglossal nerves.
Incredible feats were made during the third century BCE in both the digestive and reproductive systems. Herophilus discovered and described not only the salivary glands but also the small intestine and liver. He showed that the uterus is a hollow organ and described the ovaries and uterine tubes. He recognized that spermatozoa were produced by the testes and was the first to identify the prostate gland.
The anatomy of the muscles and skeleton is described in the *Hippocratic Corpus*, an Ancient Greek medical work written by unknown authors. Aristotle described vertebrate anatomy based on animal dissection. Praxagoras identified the difference between arteries and veins. Also in the 4th century BCE, Herophilos and Erasistratus produced more accurate anatomical descriptions based on vivisection of criminals in Alexandria during the Ptolemaic period.
In the 2nd century, Galen of Pergamum, an anatomist, clinician, writer, and philosopher, wrote the final and highly influential anatomy treatise of ancient times. He compiled existing knowledge and studied anatomy through the dissection of animals. He was one of the first experimental physiologists through his vivisection experiments on animals. Galen\'s drawings, based mostly on dog anatomy, became effectively the only anatomical textbook for the next thousand years. His work was known to Renaissance doctors only through Islamic Golden Age medicine until it was translated from Greek sometime in the 15th century.
### Medieval to early modern {#medieval_to_early_modern}
Anatomy developed little from classical times until the sixteenth century; as the historian Marie Boas writes, \"Progress in anatomy before the sixteenth century is as mysteriously slow as its development after 1500 is startlingly rapid\". Between 1275 and 1326, the anatomists Mondino de Luzzi, Alessandro Achillini and Antonio Benivieni at Bologna carried out the first systematic human dissections since ancient times. Mondino\'s *Anatomy* of 1316 was the first textbook in the medieval rediscovery of human anatomy. It describes the body in the order followed in Mondino\'s dissections, starting with the abdomen, thorax, head, and limbs. It was the standard anatomy textbook for the next century.
Leonardo da Vinci (1452--1519) was trained in anatomy by Andrea del Verrocchio. He made use of his anatomical knowledge in his artwork, making many sketches of skeletal structures, muscles and organs of humans and other vertebrates that he dissected.
Andreas Vesalius (1514--1564), professor of anatomy at the University of Padua, is considered the founder of modern human anatomy. Originally from Brabant, Vesalius published the influential book *De humani corporis fabrica* (\"the structure of the human body\"), a large format book in seven volumes, in 1543. The accurate and intricately detailed illustrations, often in allegorical poses against Italianate landscapes, are thought to have been made by the artist Jan van Calcar, a pupil of Titian.
In England, anatomy was the subject of the first public lectures given in any science; these were provided by the Company of Barbers and Surgeons in the 16th century, joined in 1583 by the Lumleian lectures in surgery at the Royal College of Physicians.
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## History
### Late modern {#late_modern}
Medical schools began to be set up in the United States towards the end of the 18th century. Classes in anatomy needed a continual stream of cadavers for dissection, and these were difficult to obtain. Philadelphia, Baltimore, and New York were all renowned for body snatching activity as criminals raided graveyards at night, removing newly buried corpses from their coffins. A similar problem existed in Britain where demand for bodies became so great that grave-raiding and even anatomy murder were practised to obtain cadavers. Some graveyards were, in consequence, protected with watchtowers. The practice was halted in Britain by the Anatomy Act of 1832, while in the United States, similar legislation was enacted after the physician William S. Forbes of Jefferson Medical College was found guilty in 1882 of \"complicity with resurrectionists in the despoliation of graves in Lebanon Cemetery\".
The teaching of anatomy in Britain was transformed by Sir John Struthers, Regius Professor of Anatomy at the University of Aberdeen from 1863 to 1889. He was responsible for setting up the system of three years of \"pre-clinical\" academic teaching in the sciences underlying medicine, including especially anatomy. This system lasted until the reform of medical training in 1993 and 2003. As well as teaching, he collected many vertebrate skeletons for his museum of comparative anatomy, published over 70 research papers, and became famous for his public dissection of the Tay Whale. From 1822 the Royal College of Surgeons regulated the teaching of anatomy in medical schools. Medical museums provided examples in comparative anatomy, and were often used in teaching. Ignaz Semmelweis investigated puerperal fever and he discovered how it was caused. He noticed that the frequently fatal fever occurred more often in mothers examined by medical students than by midwives. The students went from the dissecting room to the hospital ward and examined women in childbirth. Semmelweis showed that when the trainees washed their hands in chlorinated lime before each clinical examination, the incidence of puerperal fever among the mothers could be reduced dramatically. Before the modern medical era, the primary means for studying the internal structures of the body were dissection of the dead and inspection, palpation, and auscultation of the living. The advent of microscopy opened up an understanding of the building blocks that constituted living tissues. Technical advances in the development of achromatic lenses increased the resolving power of the microscope, and around 1839, Matthias Jakob Schleiden and Theodor Schwann identified that cells were the fundamental unit of organization of all living things. The study of small structures involved passing light through them, and the microtome was invented to provide sufficiently thin slices of tissue to examine. Staining techniques using artificial dyes were established to help distinguish between different tissue types. Advances in the fields of histology and cytology began in the late 19th century along with advances in surgical techniques allowing for the painless and safe removal of biopsy specimens. The invention of the electron microscope brought a significant advance in resolution power and allowed research into the ultrastructure of cells and the organelles and other structures within them. About the same time, in the 1950s, the use of X-ray diffraction for studying the crystal structures of proteins, nucleic acids, and other biological molecules gave rise to a new field of molecular anatomy.
Equally important advances have occurred in *non-invasive* techniques for examining the body\'s interior structures. X-rays can be passed through the body and used in medical radiography and fluoroscopy to differentiate interior structures that have varying degrees of opaqueness. Magnetic resonance imaging, computed tomography, and ultrasound imaging have all enabled the examination of internal structures in unprecedented detail to a degree far beyond the imagination of earlier generations
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In propositional logic, **affirming the consequent** (also known as **converse error**, **fallacy of the converse**, or **confusion of necessity and sufficiency**) is a formal fallacy (or an invalid form of argument) that is committed when, in the context of an indicative conditional statement, it is stated that because the consequent is true, therefore the antecedent is true. It takes on the following form:
:
: If *P*, then *Q*.
: *Q*.
: Therefore, *P*.
which may also be phrased as
: $P \rightarrow Q$ (P implies Q)
: $\therefore Q \rightarrow P$ (therefore, Q implies P)
For example, it may be true that a broken lamp would cause a room to become dark. It is not true, however, that a dark room implies the presence of a broken lamp. There may be no lamp (or any light source). The lamp may also be off. In other words, the consequent (a dark room) can have other antecedents (no lamp, off-lamp), and so can still be true even if the stated antecedent is not.
Converse errors are common in everyday thinking and communication and can result from, among other causes, communication issues, misconceptions about logic, and failure to consider other causes.
A related fallacy is denying the antecedent. Two related *valid* forms of logical argument include *modus tollens* (denying the consequent) and *modus ponens* (affirming the antecedent).
## Formal description {#formal_description}
Affirming the consequent is the action of taking a true statement $P \to Q$ and invalidly concluding its converse $Q \to P$. The name *affirming the consequent* derives from using the consequent, *Q*, of $P \to Q$, to conclude the antecedent *P*. This fallacy can be summarized formally as $(P \to Q, Q)\to P$ or, alternatively, $\frac{P \to Q, Q}{\therefore P}$. The root cause of such a logical error is sometimes failure to realize that just because *P* is a *possible* condition for *Q*, *P* may not be the *only* condition for *Q*, i.e. *Q* may follow from another condition as well.
Affirming the consequent can also result from overgeneralizing the experience of many statements *having* true converses. If *P* and *Q* are \"equivalent\" statements, i.e. $P \leftrightarrow Q$, it *is* possible to infer *P* under the condition *Q*. For example, the statements \"It is August 13, so it is my birthday\" $P \to Q$ and \"It is my birthday, so it is August 13\" $Q \to P$ are equivalent and both true consequences of the statement \"August 13 is my birthday\" (an abbreviated form of $P \leftrightarrow Q$).
Of the possible forms of \"mixed hypothetical syllogisms,\" two are valid and two are invalid. Affirming the antecedent (modus ponens) and denying the consequent (modus tollens) are valid. Affirming the consequent and denying the antecedent are invalid.
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## Additional examples {#additional_examples}
**Example 1**
One way to demonstrate the invalidity of this argument form is with a counterexample with true premises but an obviously false conclusion. For example:
: If someone lives in San Diego, then they live in California.
: Joe lives in California.
: Therefore, Joe lives in San Diego.
There are many places to live in California other than San Diego. On the other hand, one can affirm with certainty that \"if someone does not live in California\" (*non-Q*), then \"this person does not live in San Diego\" (*non-P*). This is the contrapositive of the first statement, and it must be true if and only if the original statement is true.
**Example 2**
: If an animal is a dog, then it has four legs.
: My cat has four legs.
: Therefore, my cat is a dog.
Here, it is immediately intuitive that any number of other antecedents (\"If an animal is a deer\...\", \"If an animal is an elephant\...\", \"If an animal is a moose\...\", *etc.*) can give rise to the consequent (\"then it has four legs\"), and that it is preposterous to suppose that having four legs *must* imply that the animal is a dog and nothing else. This is useful as a teaching example since most people can immediately recognize that the conclusion reached must be wrong (intuitively, a cat cannot be a dog), and that the method by which it was reached must therefore be fallacious. This argument was featured in Euguene Ionesco\'s Rhinoceros in a conversation between a Logician and an Old Gentleman.
**Example 3**
In *Catch-22*, the chaplain is interrogated for supposedly being \"Washington Irving\"/\"Irving Washington\", who has been blocking out large portions of soldiers\' letters home. The colonel has found such a letter, but with the chaplain\'s name signed.
: \"You can read, though, can\'t you?\" the colonel persevered sarcastically. \"The author signed his name.\"
: \"That\'s my name there.\"
: \"Then you wrote it. Q.E.D.\"
*P* in this case is \'The chaplain signs his own name\', and *Q* \'The chaplain\'s name is written\'. The chaplain\'s name may be written, but he did not necessarily write it, as the colonel falsely concludes
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The current political regime in Angola is presidentialism, in which the President of the Republic is also head of state and government; it is advised by a Council of Ministers, which together with the President form the national executive power. Legislative power rests with the 220 parliamentarians elected to the National Assembly. The President of the Republic, together with the parliament, appoints the majority of the members of the two highest bodies of the judiciary, that is, the Constitutional Court and the Supreme Court. The judiciary is still made up of the Court of Auditors and the Supreme Military Court.
The Angolan government is composed of three branches of government: executive, legislative and judicial. For decades, political power has been concentrated in the presidency with the People\'s Movement for the Liberation of Angola. `{{Politics of Angola}}`{=mediawiki}
## History
Since the adoption of a new constitution in 2010, the politics of Angola takes place in a framework of a presidential republic, whereby the President of Angola is both head of state and head of government, and of a multi-party system. Executive power is exercised by the government. Legislative power is vested in the President, the government and parliament.
Angola changed from a one-party Marxist-Leninist system ruled by the Popular Movement for the Liberation of Angola (MPLA), in place since independence in 1975, to a multiparty democracy based on a new constitution adopted in 1992. That same year the first parliamentary and presidential elections were held. The MPLA won an absolute majority in the parliamentary elections. In the presidential elections, President José Eduardo dos Santos won the first round election with more than 49% of the vote to Jonas Savimbi\'s 40%. A runoff election would have been necessary, but never took place. The renewal of civil war immediately after the elections, which were considered as fraudulent by UNITA, and the collapse of the Lusaka Protocol, created a split situation. To a certain degree the new democratic institutions worked, notably the National Assembly, with the active participation of UNITA\'s and the FNLA\'s elected MPs - while José Eduardo dos Santos continued to exercise his functions without democratic legitimation. However the armed forces of the MPLA (now the official armed forces of the Angolan state) and of UNITA fought each other until the leader of UNITA, Jonas Savimbi, was killed in action in 2002.
From 2002 to 2010, the system as defined by the constitution of 1992 functioned in a relatively normal way. The executive branch of the government was composed of the President, the Prime Minister and Council of Ministers. The Council of Ministers, composed of all ministers and vice ministers, met regularly to discuss policy issues. Governors of the 18 provinces were appointed by and served at the pleasure of the president. The Constitutional Law of 1992 established the broad outlines of government structure and the rights and duties of citizens. The legal system was based on Portuguese and customary law but was weak and fragmented. Courts operated in only 12 of more than 140 municipalities. A Supreme Court served as the appellate tribunal; a Constitutional Court with powers of judicial review was never constituted despite statutory authorization. In practice, power was more and more concentrated in the hands of the President who, supported by an ever-increasing staff, largely controlled parliament, government, and the judiciary.
The 26-year-long civil war has ravaged the country\'s political and social institutions. The UN estimates of 1.8 million internally displaced persons (IDPs), while generally the accepted figure for war-affected people is 4 million. Daily conditions of life throughout the country and specifically Luanda (population approximately 6 million) mirror the collapse of administrative infrastructure as well as many social institutions. The ongoing grave economic situation largely prevents any government support for social institutions. Hospitals are without medicines or basic equipment, schools are without books, and public employees often lack the basic supplies for their day-to-day work.
José Eduardo dos Santos stepped down as President of Angola after 38 years in 2017, being peacefully succeeded by João Lourenço, Santos\' chosen successor. However, President João Lourenço started a campaign against corruption of the dos Santos era. In November 2017, Isabel dos Santos, the billionaire daughter of former President José Eduardo dos Santos, was fired from her position as head of the country\'s state oil company Sonangol. In August 2020, José Filomeno dos Santos, son of Angola\'s former president, was sentenced for five years in jail for fraud and corruption.
In August 2022, the ruling party, MPLA, won another outright majority and President Joao Lourenco won a second five-year term in the election. However, the election was the tightest in Angola\'s history.
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## Executive branch {#executive_branch}
The 2010 constitution grants the President almost absolute power. Elections for the National assembly are to take place every five years, and the President is automatically the leader of the winning party or coalition. It is for the President to appoint (and dismiss) all of the following:
- The members of the government (state ministers, ministers, state secretaries and vice-ministers);
- The members of the Constitutional Court;
- The members of the Supreme Court;
- The members of the Court of Auditors;
- The members of the Military Supreme Court;
- The Governor and Vice-Governors of the National Angolan Bank;
- The General-Attorney, the Vice-General-Attorneys and their deputies (as well as the military homologous);
- The Governors of the provinces;
- The members of the Republic Council;
- The members of the National Security Council;
- The members of the Superior Magistrates Councils;
- The General Chief of the Armed Forces and his deputy;
- All other command posts in the military;
- The Police General Commander, and the 2nd in command;
- All other command posts in the police;
- The chiefs and directors of the intelligence and security organs.
The President is also provided a variety of powers, like defining the policy of the country. Even though it\'s not up to him/her to make laws (only to promulgate them and make edicts), the President is the leader of the winning party. The only \"relevant\" post that is not directly appointed by the President is the vice-president, which is the second in the winning party.
José Eduardo dos Santos stepped down as President of Angola after 38 years in 2017, being peacefully succeeded by João Lourenço, Santos\' chosen successor.
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## Legislative branch {#legislative_branch}
The National Assembly (*Assembleia Nacional*) has 223 members, elected for a four-year term, 130 members by proportional representation, 90 members in provincial districts, and 3 members to represent Angolans abroad. The general elections in 1997 were rescheduled for 5 September 2008. The ruling party MPLA won 82% (191 seats in the National Assembly) and the main opposition party won only 10% (16 seats). The elections however have been described as only partly free but certainly not fair. A White Book on the elections in 2008 lists up all irregularities surrounding the Parliamentary elections of 2008.
## Political parties and elections {#political_parties_and_elections}
## Judicial branch {#judicial_branch}
Supreme Court (or \"Tribunal da Relacao\") judges of the Supreme Court are appointed by the president. The Constitutional Court, with the power of judicial review, contains 11 justices. Four are appointed by the President, four by the National Assembly, two by the Superior Council of the Judiciary, and one elected by the public
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**Transport in Angola** comprises:
## Roads
Two trans-African automobile routes pass through Angola:
- the Tripoli-Cape Town Highway
- the Beira-Lobito Highway
Map of Trans-African Highways.PNG\|Map of Trans-African Highways.
Walking home.jpg\|Walking home on EN 105. Tired are they.jpg\|Donkey-drawn carts. Transportation Jingu.jpg\|Three-wheeled motorcycles. The riches transportation.jpg\|Trucks. Midd Town Luanda.jpg\|Automobiles in Luanda. The Nowhere road.jpg\|New highway (2019).
## Railways
There are three separate railway lines in Angola:
- Luanda Railway (CFL) (northern);
- Benguela Railway (CFB) (central), operated by the Lobito Atlantic Railway joint venture;
- Moçâmedes Railway (CFM) (southern);
Reconstruction of these three lines began in 2005 and they are now all operational. The Benguela Railway connects to the Democratic Republic of the Congo.
## Waterways
- 1,300 km navigable (2008)
: *country comparison to the world:* 36
## Pipelines
- gas 352 km; liquid petroleum gas 85 km; crude oil 1,065 km (2013)
In April 2012, the Zambian Development Agency (ZDA) and an Angolan company signed a memorandum of understanding (MoU) to build a multi-product pipeline from Lobito to Lusaka, Zambia, to deliver various refined products to Zambia.
Angola plans to build an oil refinery in Lobito in the coming years.
## Ports and harbors {#ports_and_harbors}
The government plans to build a deep-water port at Barra do Dande, north of Luanda, in Bengo province near Caxito.
## Merchant marine {#merchant_marine}
- *total:* 58
: *country comparison to the world:* 115
- *by type:* cargo 13, oil tanker 8, other 37 (2008)
## Airports
- 102 (2021)
The old airport in Luanda, Quatro de Fevereiro Airport, will be replaced by the new Dr. Antonio Agostinho Neto International Airport
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The **Angolan Armed Forces** (*Forças Armadas Angolanas*) or **FAA** is the military of Angola. The FAA consist of the Angolan Army (*Exército Angolano*), the Angolan Navy (*Marinha de Guerra Angolana*) and the National Air Force of Angola (*Força Aérea Nacional de Angola*). Reported total manpower in 2021 was about 107,000. The FAA is headed by the Chief of the General Staff António Egídio de Sousa Santos since 2018, who reports to the minister of National Defense, currently João Ernesto dos Santos.
## History
### Roots
The FAA succeeded to the previous People\'s Armed Forces for the Liberation of Angola (FAPLA) following the abortive Bicesse Accord with the Armed Forces of the Liberation of Angola (FALA), armed wing of the National Union for the Total Independence of Angola (UNITA). As part of the peace agreement, troops from both armies were to be demilitarized and then integrated. Integration was never completed as UNITA and FALA went back to war in 1992. Later, consequences for FALA personnel in Luanda were harsh with FAPLA veterans persecuting their erstwhile opponents in certain areas and reports of vigilantism.
### Founding
The Angolan Armed Forces were created on 9 October 1991. The institutionalization of the FAA was made in the Bicesse Accords, signed in 1991, between the Angolan Government and UNITA. The principles that would govern the FAA were defined in a joint proposal presented on September 24, 1991, and approved on 9 October. On 14 November 1991, Generals João Baptista de Matos and Abílio Kamalata Numa were appointed to the Superior Command of the Armed Forces. The ceremony took place at the Hotel Presidente Luanda, and was presided over by the then-minister França Vandúnem.
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## Branches
### Army
The Army (*Exército*) is the land component of the FAA. It is organized in six military regions (Cabinda, Luanda, North, Center, East and South), with an infantry division being based in each one. Distributed by the six military regions / infantry divisions, there are 25 motorized infantry brigades, one tank brigade and one engineering brigade. The Army also includes an artillery regiment, the Military Artillery School, the Army Military Academy, an anti-aircraft defense group, a composite land artillery group, a military police regiment, a logistical transportation regiment and a field artillery brigade. The Army further includes the Special Forces Brigade (including Commandos and Special Operations units), but this unit is under the direct command of the General Staff of the FAA.
### Air Force {#air_force}
The National Air Force of Angola (FANA, *Força Aérea Nacional de Angola*) is the air component of the FAA. It is organized in six aviation regiments, each including several squadrons. To each of the regiments correspond an air base. Besides the aviation regiments, there is also a Pilot Training School.
The Air Force\'s personnel total about 8,000; its equipment includes transport aircraft and six Russian-manufactured Sukhoi Su-27 fighter aircraft. In 2002, one was lost during the civil war with UNITA forces.
In 1991, the Air Force/Air Defense Forces had 8,000 personnel and 90 combat-capable aircraft, including 22 fighters, 59 fighter ground attack aircraft and 16 attack helicopters.
### Navy
The Angola Navy (MGA, *Marinha de Guerra de Angola*) is the naval component of the FAA. It is organized in two naval zones (North and South), with naval bases in Luanda, Lobito and Moçâmedes. It includes a Marines Brigade and a Marines School, based in Ambriz. The Navy numbers about 1,000 personnel and operates only a handful of small patrol craft and barges.
The Navy has been neglected and ignored as a military arm mainly due to the guerrilla struggle against the Portuguese and the nature of the civil war. From the early 1990s to the present the Angolan Navy has shrunk from around 4,200 personnel to around 1,000, resulting in the loss of skills and expertise needed to maintain equipment. Portugal has been providing training through its Technical Military Cooperation (CTM) programme. The Navy is requesting procurement of a frigate, three corvettes, three offshore patrol vessel and additional fast patrol boats.
Most of the vessels in the navy\'s inventory dates back from the 1980s or earlier, and many of its ships are inoperable due to age and lack of maintenance. However the navy acquired new boats from Spain and France in the 1990s. Germany has delivered several Fast Attack Craft for border protection in 2011.
In September 2014 it was reported that the Angolan Navy would acquire seven Macaé-class patrol vessels from Brazil as part of a Technical Memorandum of Understanding (MoU) covering the production of the vessels as part of Angola\'s Naval Power Development Programme (Pronaval). The military of Angola aims to modernize its naval capability, presumably due to a rise in maritime piracy within the Gulf of Guinea which may have an adverse effect on the country\'s economy.
The navy\'s current known inventory includes the following:
- Fast attack craft
- 4 Mandume class craft (Bazan Cormoran type, refurbished in 2009)
- Patrol boats
- 3 18.3m long Patrulheiro patrol boats (refurbished in 2002)
- 5 ARESA PVC-170
- 2 Namacurra-class harbour patrol boats
- Fisheries Patrol Boats
- Ngola Kiluange and Nzinga Mbandi (delivered in September and October 2012 from Damen Shipyards)(Operated by Navy personnel under the Ministry of Agriculture, Rural Development and Fisheries)
- 28-metre FRV 2810 (Pensador) (Operated by Navy personnel under the Ministry of Agriculture, Rural Development and Fisheries)
- Landing craft
- LDM-400 -- 1 or 3 (reportedly has serviceability issues)
- Coastal defense equipment (CRTOC)
- SS-C1 Sepal radar system
The navy also has several aircraft for maritime patrol:
Aircraft Origin Type Versions In service Notes
------------ --------------- ------------------ ---------- ------------ -------
Fokker F27 Netherlands Medium transport 2
EMB 111 Brazil Maritime patrol 6
Boeing 707 United States Maritime patrol 1
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## Specialized units {#specialized_units}
### Special forces {#special_forces}
The FAA include several types of special forces, namely the Commandos, the Special Operations and the Marines. The Angolan special forces follow the general model of the analogous Portuguese special forces, receiving similar training.
The Commandos and the Special forces are part of the Special Forces Brigade (BRIFE, *Brigada de Forças Especiais*), based at Cabo Ledo, in the Bengo Province. The BRIFE includes two battalions of commandos, a battalion of special operations and sub-units of combat support and service support. The BRIFE also included the Special Actions Group (GAE, *Grupo de Ações Especiais*), which is presently inactive and that was dedicated to long range reconnaissance, covert and sabotage operations. In the Cabo Ledo base is also installed the Special Forces Training School (EFFE, *Escola de Formação de Forças Especiais*). Both the BRIFE and the EFFE are directly under the Directorate of Special Forces of the General Staff of the Armed Forces.
The marines (*fuzileiros navais*) constitute the Marines Brigade of the Angolan Navy. The Marines Brigade is not permanently dependent of the Directorate of Special Forces, but can detach their units and elements to be put under the command of that body for the conduction of exercises or real operations. The Marines have a special forces unit known as Special Operations Marines(FOE, Fuzileiros Operaçües Especiais).
Since the disbandment of the Angolan Parachute Battalion in 2004, the FAA do not have a specialized paratrooper unit. However, elements of the commandos, special operations and marines are parachute qualified.
### Territorial troops {#territorial_troops}
The Directorate of People\'s Defense and Territorial Troops of the Defence Ministry or ODP was established in late 1975. It had 600,000 members, having personnel in virtually every village by 1979. It had both armed and unarmed units dispersed in villages throughout the country. The People\'s Vigilance Brigades (*Brigadas Populares de Vigilância, BPV*) also serve a similar purpose.
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## Training establishments {#training_establishments}
### Armed Forces Academy {#armed_forces_academy}
The Military Academy (*Academia Militar do Exército, AMEx*) is a military university public higher education establishment whose mission is to train officers of the Permanent Staff of the Army. It has been in operation since 21 August 2009 by presidential decree. Its headquarters are in Lobito. It trains in the following specialties:
- Infantry
- Tanks
- Land Artillery
- Anti-Air Defense
- Military Engineering
- Logistics
- Telecommunications
- Hidden Direction of Troops
- Military Administration
- Armament and Technique
- Chemical Defense
- Operational Military Intelligence
- Technical Repair and Maintenance Platoon of Auto and Armored Technique
### Navy {#navy_1}
- Naval War Institute (INSG)
- Naval Academy
- Naval Specialist School
### Air Force {#air_force_1}
- Angolan Military Aviation School
- Pilot Basic Training School (Lobito)
## Institutions/other units {#institutionsother_units}
### Museum of the Armed Forces {#museum_of_the_armed_forces}
### Military Hospitals {#military_hospitals}
The Military hospital of the FAA is the Main Military Hospital. It has the following lineage:
- 1961 -- Evacuation Infirmary
- 1962 -- Military Hospital of Luanda
- 1975 -- Military Hospital
- 1976 -- Central Military Hospital
- 1989 -- Main Military Hospital
It provides specialized medical assistance in accordance with the military health system; It also promotes post-graduate education and scientific research. Currently, the Main Military Hospital serves 39 special medical specialties. It is a headed by a Director General whose main supporting body is the board of directors.
### Supreme Military Court {#supreme_military_court}
The Supreme Military Court is the highest organ of the hierarchy of military courts. The Presiding Judge, the Deputy Presiding Judge and the other Counselor Judges of the Supreme Military Court are appointed by the President of the Republic. The composition, organization, powers and functioning of the Supreme Military Court are established by law.
### Military Bands {#military_bands}
The FAA maintains Portuguese-style military bands in all three branches and in individual units. The primary band is the 100-member Music Band of the Presidential Security Household. The music band of the Army Command was created on 16 June 1994 and four years later, on 15 August 1998, the National Air Force created a music band within an artistic brigade. The navy has its own marching band, as well as a small musical group known as *Banda 10 de Julho* (10 July Band), based at the Luanda Naval Base.
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## Foreign deployments {#foreign_deployments}
The FAPLA\'s main counterinsurgency effort was directed against UNITA in the southeast, and its conventional capabilities were demonstrated principally in the undeclared South African Border War. The FAPLA first performed its external assistance mission with the dispatch of 1,000 to 1,500 troops to São Tomé and Príncipe in 1977 to bolster the socialist regime of President Manuel Pinto da Costa. During the next several years, Angolan forces conducted joint exercises with their counterparts and exchanged technical operational visits. The Angolan expeditionary force was reduced to about 500 in early 1985.
The Angolan Armed Forces were controversially involved in training the armed forces of fellow Lusophone states Cape Verde and Guinea-Bissau. In the case of the latter, the 2012 Guinea-Bissau coup d\'état was cited by the coup leaders as due to Angola\'s involvement in trying to \"reform\" the military in connivance with the civilian leadership.
Occasionally skirmishes on the DRC-Angola border happening, sometimes also in connection with the Cabinda conflict. In 2020 one Angolan soldier died after a gun battle with congolese forces in Kasai region on DRC territory. A presence during the unrest in Ivory Coast, 2010--2011, were not officially confirmed. However, the *\[\[Frankfurter Allgemeine Zeitung\]\]*, citing *Jeune Afrique*, said that among President Gbagbo\'s guards were 92 personnel of President Dos Santos\'s Presidential Guard Unit. Angola is basically interested in the participation of the FAA operations of the African Union and has formed special units for this purpose.
In 2021, the Angolan Parliament approved integration of FAA into Southern African Development Community (SADC)\'s mission for peace in Cabo Delgado, Mozambique. Angola sent a team of 20 officers to participate
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The **foreign relations of Angola** are based on Angola\'s strong support of U.S. foreign policy as the Angolan economy is dependent on U.S. foreign aid. From 1975 to 1989, Angola was aligned with the Eastern bloc, in particular the Soviet Union, Libya, and Cuba. Since then, it has focused on improving relationships with Western countries, cultivating links with other Portuguese-speaking countries, and asserting its own national interests in Central Africa through military and diplomatic intervention. In 1993, it established formal diplomatic relations with the United States. It has entered the Southern African Development Community as a vehicle for improving ties with its largely Anglophone neighbors to the south. Zimbabwe and Namibia joined Angola in its military intervention in the Democratic Republic of the Congo, where Angolan troops remain in support of the Joseph Kabila government. It also has intervened in the Republic of the Congo (Brazzaville) in support of Denis Sassou-Nguesso in the civil war.
Since 1998, Angola has successfully worked with the United Nations Security Council to impose and carry out sanctions on UNITA. More recently, it has extended those efforts to controls on conflict diamonds, the primary source of revenue for UNITA during the Civil War that ended in 2002. At the same time, Angola has promoted the revival of the Community of Portuguese-Speaking Countries (CPLP) as a forum for cultural exchange and expanding ties with Portugal (its former ruler) and Brazil (which shares many cultural affinities with Angola) in particular. Angola is a member of the Port Management Association of Eastern and Southern Africa (PMAESA).
## Diplomatic relations {#diplomatic_relations}
List of countries which Angola maintains diplomatic relations with:
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## Bilateral relations {#bilateral_relations}
### Africa
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Country | Formal Relations Began | Notes |
+=========+========================+=================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+
| | 30 October 1977 | See Angola--Cape Verde relations |
| | | |
| | | Cape Verde signed a friendship accord with Angola in December 1975, shortly after Angola gained its independence. Cape Verde and Guinea-Bissau served as stop-over points for Cuban troops on their way to Angola to fight UNITA rebels and South African troops. Prime Minister Pedro Pires sent FARP soldiers to Angola where they served as the personal bodyguards of Angolan President José Eduardo dos Santos. |
| | | |
| | | - Angola has an embassy in Praia. |
| | | - Cape Verde has an embassy in Luanda and a consulate in Benguela. |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 17 October 1978 | Many thousands of Angolans fled the country after the civil war. More than 20,000 people were forced to leave the Democratic Republic of the Congo in 2009, an action the DR Congo said was in retaliation for regular expulsion of Congolese diamond miners who were in Angola illegally. Angola sent a delegation to DR Congo\'s capital Kinshasa and succeeded in stopping government-forced expulsions which had become a \"tit-for-tat\" immigration dispute. \"Congo and Angola have agreed to suspend expulsions from both sides of the border,\" said Lambert Mende, DR Congo information minister, in October 2009. \"We never challenged the expulsions themselves; we challenged the way they were being conducted -- all the beating of people and looting their goods, even sometimes their clothes,\" Mende said. |
| | | |
| | | - Angola has an embassy in Kinshasa. |
| | | - DR Congo has an embassy in Luanda. |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | | See Angola--Kenya relations |
| | | |
| | | - Angola has an embassy in Nairobi. |
| | | - Kenya has an embassy in Luanda. |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 5 July 1975 | See Angola--Mozambique relations |
| | | |
| | | - Angola has an embassy in Maputo. |
| | | - Mozambique has an embassy in Luanda. |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 18 September 1990 | See Angola--Namibia relations |
| | | |
| | | Namibia borders Angola to the south. In 1999, Namibia signed a mutual defense pact with its northern neighbor Angola.{{cite web |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 15 March 1976 | See Angola--Nigeria relations |
| | | |
| | | Angolan-Nigerian relations are primarily based on their roles as oil exporting nations. Both are members of the Organization of the Petroleum Exporting Countries, the African Union and other multilateral organizations. |
| | | |
| | | - Angola has an embassy in Abuja. |
| | | - Nigeria has an embassy in Luanda. |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 17 May 1994 | See Angola--South Africa relations |
| | | |
| | | Angola-South Africa relations are quite strong as the ruling parties in both nations, the African National Congress in South Africa and the MPLA in Angola, fought together during the Angolan Civil War and South African Border War. They fought against UNITA rebels, based in Angola, and the apartheid-era government in South Africa who supported them. Nelson Mandela mediated between the MPLA and UNITA factions during the last years of Angola\'s civil war. |
| | | |
| | | - Angola has an embassy in Pretoria and consulates-general in Cape Town and Johannesburg. |
| | | - South Africa has an embassy in Luanda. |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 15 October 1982 | See Angola--Zimbabwe relations |
+---------+------------------------+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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## Bilateral relations {#bilateral_relations}
### Americas
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Country | Formal Relations Began | Notes |
+=========+========================+============================================================================================================================================================================================================================================================================================================================================================================================================================================================================+
| | 2 June 1979 | Both countries established diplomatic relations on 2 June 1979 See Angola--Argentina relations |
| | | |
| | | - Angola has an embassy in Buenos Aires. |
| | | - Argentina has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 12 November 1975 | See Angola--Brazil relations |
| | | |
| | | Commercial and economic ties dominate the relations of each country. Parts of both countries were part of the Portuguese Empire from the early 16th century until Brazil\'s independence in 1822. As of November 2007, \"trade between the two countries is booming as never before\" |
| | | |
| | | - Angola has an embassy in Brasília and consulates-general in Rio de Janeiro and São Paulo. |
| | | - Brazil has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 1 February 1978 | Both countries established diplomatic relations on 1 February 1978 |
| | | |
| | | Canada-Angola relations were established in 1978, and Canada is accredited to Angola from its embassy in Harare, Zimbabwe. Ties have grown since the end of the civil war in 2002, with increased engagement in areas of mutual interest. As Chair of the United Nations Security Council\'s Angola Sanctions Committee, Canada limited the ability of UNITA to continue its military campaign, sanctions helped to bring a ceasefire agreement to end Angola\'s conflict. |
| | | |
| | | - Angola is accredited to Canada from its embassy in Washington, D.C., United States. |
| | | - Canada is accredited to Angola from its embassy in Harare, Zimbabwe and maintains an honorary consulate in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 15 November 1975 | See Angola--Cuba relations |
| | | |
| | | During Angola\'s civil war Cuban forces fought to install a Marxist--Leninist MPLA-PT government, against Western-backed UNITA and FLNA guerrillas and the South-African army. |
| | | |
| | | - Angola has an embassy in Havana. |
| | | - Cuba has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 20 February 1976 | Both countries established diplomatic relations on 20 February 1976 See Angola--Mexico relations |
| | | |
| | | - Angola is accredited to Mexico from its embassy in Washington, D.C., United States. |
| | | - Mexico is accredited to Angola from its embassy in Pretoria, South Africa and maintains an honorary consulate in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 14 July 1994 | Both countries established diplomatic relations on 14 July 1994 See Angola--United States relations From the mid-1980s through at least 1992, the United States was the primary source of military and other support for the UNITA rebel movement, which was led from its creation through 2002 by Jonas Savimbi. The U.S. refused to recognize Angola diplomatically during this period. |
| | | |
| | | Relations between the United States of America and the Republic of Angola (formerly the People\'s Republic of Angola) have warmed since Angola\'s ideological renunciation of Communism before the 1992 elections. |
| | | |
| | | - Angola has an embassy in Washington, D.C., and consulates-general in Houston and New York City. |
| | | - United States has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 6 March 1987 | Both countries established diplomatic relations on 6 March 1987 See Angola--Uruguay relations |
| | | |
| | | - Angola has a consulate-general in Montevideo. |
| | | - Uruguay is accredited to Angola from its embassy in Pretoria, South Africa. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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## Bilateral relations {#bilateral_relations}
### Asia
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Country | Formal Relations Began | Notes |
+=========+========================+==================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+
| | 12 January 1983 | Both countries established diplomatic relations on 12 January 1983 See Angola--China relations |
| | | |
| | | Chinese prime minister Wen Jiabao visited Angola in June 2006, offering a US\$9 billion loan for infrastructure improvements in return for petroleum. The PRC has invested heavily in Angola since the end of the civil war in 2002. João Manuel Bernardo, the current ambassador of Angola to China, visited the PRC in November 2007. |
| | | |
| | | - Angola has an embassy in Beijing and a consulate-general in Macau. |
| | | - China has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 2 June 1979 | Both countries established diplomatic relations on 2 June 1979 See Angola--India relations |
| | | |
| | | - Angola has an embassy in New Delhi. |
| | | - India has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 16 April 1992 | See Angola--Israel relations |
| | | |
| | | Angola-Israel relations, primarily based on trade and pro-United States foreign policies, are excellent. In March 2006, the trade volume between the two countries amounted to \$400 million. In 2005, President José Eduardo dos Santos visited Israel. |
| | | |
| | | - [Angola/Israel business volume amounted at USD 400 million](https://web.archive.org/web/20141225062707/http://www.angoladigital.net/negocios/index.php?Itemid=47&id=150&option=com_content&task=view) Angola Press, 22 March 2006 |
| | | - [Israeli Ambassador Highlights Relations With Angola](https://web.archive.org/web/20060517045254/http://www.angolapress-angop.ao/noticia-e.asp?ID=437778) Angola Press |
| | | - Angola has an embassy in Tel Aviv. |
| | | - Israel has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | September 1976 | See Angola--Japan relations |
| | | |
| | | Diplomatic relations between Japan and Angola were established in September 1976. Japan has donated towards demining following the civil war. |
| | | |
| | | - Angola has an embassy in Tokyo. |
| | | - Japan has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 20 October 1977 | Both countries established diplomatic relations on 20 October 1977 |
| | | |
| | | The Government of Angola called for the support of Pakistan for the candidature of Angola to the seat of non-permanent member of the UN Security Council, whose election is set for September this year, during the 69th session of the General Assembly of United Nations. On the fringes of the ceremony, the Angolan diplomat also met with officials in charge of the economic and commercial policy of Pakistan, to assess the business opportunities between the two states. It asked to discuss aspects related to the cooperation on several domains of common interest. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 14 September 2001 | Both countries established diplomatic relations on 14 September 2001. |
| | | |
| | | - Angola has an embassy in Manila. |
| | | - Philippines is accredited to Angola from its embassy in Lisbon, Portugal. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 9 July 1980 | Both countries established diplomatic relations on 9 July 1980 See Angola--Turkey relations |
| | | |
| | | - Angola has an embassy in Ankara. |
| | | - Turkey has an embassy in Luanda. |
| | | - Trade volume between the two countries was US\$212 million in 2019. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 12 November 1975 | Both countries established diplomatic relations on 12 November 1975 See Angola--Vietnam relations |
| | | |
| | | Angola-Vietnam relations were established on 12 November 1975 after Angola gained its independence, when future president of Angola Agostinho Neto visited Vietnam. Angola and Vietnam have steadfast partners as both transitioned from Cold War-era foreign policies of international communism to pro-Western pragmatism following the fall of the Soviet Union. |
| | | |
| | | - Angola has an embassy in Hanoi. |
| | | - Vietnam has an embassy in Luanda. |
+---------+------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
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## Bilateral relations {#bilateral_relations}
### Europe
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| Country | Formal Relations Began | Notes |
+=========+========================+=====================================================================================================================================================================================================================================================================================================================================================================================================================================================================================================+
| | 17 February 1976 | See Angola--France relations |
| | | |
| | | Relations between the two countries have not always been cordial due to the former French government\'s policy of supporting militant separatists in Angola\'s Cabinda province and the international Angolagate scandal embarrassed both governments by exposing corruption and illicit arms deals. Following French president Nicolas Sarkozy\'s visit in 2008, relations have improved. |
| | | |
| | | - Angola has an embassy in Paris. |
| | | - France has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 16 August 1979 | Both countries established diplomatic relations on 16 August 1979 See Angola--Germany relations |
| | | |
| | | - Angola has an embassy in Berlin. |
| | | - Germany has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 14 April 1975 | - Angola has an embassy to the Holy See based in Rome. |
| | | - Holy See has an Apostolic Nuncio to Angola. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 4 June 1976 | See Angola--Italy relations |
| | | |
| | | - Angola has an embassy in Rome. |
| | | - Italy has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 18 February 1976 | - Angola has an embassy in The Hague and a consulate-general in Rotterdam. |
| | | - Netherlands has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 9 March 1976 | See Angola--Portugal relations |
| | | |
| | | Angola-Portugal relations have significantly improved since the Angolan government abandoned communism and nominally embraced democracy in 1991, embracing a pro-U.S. and to a lesser degree pro-Europe foreign policy. Portugal ruled Angola for 400 years, colonizing the territory from 1483 until independence in 1975. Angola\'s war for independence did not end in a military victory for either side, but was suspended as a result of a coup in Portugal that replaced the Caetano regime. |
| | | |
| | | - Angola has an embassy in Lisbon and a consulate-general in Porto. |
| | | - Portugal has an embassy in Luanda and a consulate-general in Benguela. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 11 November 1975 | Both countries established diplomatic relations on 11 November 1975 See Angola--Russia relations |
| | | |
| | | - Angola has an embassy in Moscow. |
| | | - Russia has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 12 November 1975 | Both countries established diplomatic relations on 12 November 1975 See Angola--Serbia relations |
| | | |
| | | The defence minister of Serbia, Dragan Šutanovac, stated in a 2011 meeting in Luanda that Serbia would negotiate with the Angolan military authorities for the construction of a new military hospital in Angola. |
| | | |
| | | Angola supports Serbia\'s stance on Kosovo, and recognizes Serbia\'s territorial integrity. |
| | | |
| | | - Angola has an embassy in Belgrade. |
| | | - Serbia has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 19 October 1977 | Both countries established diplomatic relations on 19 October 1977 See Angola--Spain relations |
| | | |
| | | - Angola has an embassy in Madrid. |
| | | - Spain has an embassy in Luanda. |
+---------+------------------------+-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| | 14 October 1977 | Angola established diplomatic relations with the UK on 14 October 1977. |
| | | |
| | | - Angola maintains an embassy in London. |
| | | - The United Kingdom is accredited to Angola through its embassy in Luanda. |
| | | |
| | | Both countries share common membership of the Atlantic co-operation pact, and the World Trade Organization
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`{{Use dmy dates|date=July 2020}}`{=mediawiki} An **android** is a humanoid robot or other artificial being, often made from a flesh-like material. Historically, androids existed only in the domain of science fiction and were frequently seen in film and television, but advances in robot technology have allowed the design of functional and realistic humanoid robots.
## Terminology
The *Oxford English Dictionary* traces the earliest use (as \"Androides\") to Ephraim Chambers\' 1728 *Cyclopaedia,* in reference to an automaton that St. Albertus Magnus allegedly created. By the late 1700s, \"androides\", elaborate mechanical devices resembling humans performing human activities, were displayed in exhibit halls. The term \"android\" appears in US patents as early as 1863 in reference to miniature human-like toy automatons. The term *android* was used in a more modern sense by the French author Auguste Villiers de l\'Isle-Adam in his work *Tomorrow\'s Eve* (1886), featuring an artificial humanoid robot named Hadaly. The term made an impact into English pulp science fiction starting from Jack Williamson\'s *The Cometeers* (1936) and the distinction between mechanical robots and fleshy androids was popularized by Edmond Hamilton\'s Captain Future stories (1940--1944).
Although Karel Čapek\'s robots in *R.U.R. (Rossum\'s Universal Robots)* (1921)---the play that introduced the word *robot* to the world---were organic artificial humans, the word \"robot\" has come to primarily refer to mechanical humans, animals, and other beings. The term \"android\" can mean either one of these, while a cyborg (\"cybernetic organism\" or \"bionic man\") would be a creature that is a combination of organic and mechanical parts.
The term \"droid\", popularized by George Lucas in the original *Star Wars* film and now used widely within science fiction, originated as an abridgment of \"android\", but has been used by Lucas and others to mean any robot, including distinctly non-human form machines like R2-D2. The word \"android\" was used in *Star Trek: The Original Series* episode \"What Are Little Girls Made Of?\" The abbreviation \"andy\", coined as a pejorative by writer Philip K. Dick in his novel *Do Androids Dream of Electric Sheep?*, has seen some further usage, such as within the TV series *Total Recall 2070*.
While the term \"android\" is used in reference to human-looking robots in general (not necessarily male-looking humanoid robots), a robot with a female appearance can also be referred to as a *gynoid*. Besides one can refer to robots without alluding to their sexual appearance by calling them *anthrobots* (a portmanteau of anthrōpos and robot; see *anthrobotics*) or *anthropoids* (short for anthropoid robots; the term *humanoids* is not appropriate because it is already commonly used to refer to human-like organic species in the context of science fiction, futurism and speculative astrobiology).
Authors have used the term *android* in more diverse ways than *robot* or *cyborg*. In some fictional works, the difference between a robot and android is only superficial, with androids being made to look like humans on the outside but with robot-like internal mechanics. In other stories, authors have used the word \"android\" to mean a wholly organic, yet artificial, creation. Other fictional depictions of androids fall somewhere in between.
Eric G. Wilson, who defines an android as a \"synthetic human being\", distinguishes between three types of android, based on their body\'s composition:
- the mummy type -- made of \"dead things\" or \"stiff, inanimate, natural material\", such as mummies, puppets, dolls and statues
- the golem type -- made from flexible, possibly organic material, including golems and homunculi
- the automaton type -- made from a mix of dead and living parts, including automatons and robots
Although human morphology is not necessarily the ideal form for working robots, the fascination in developing robots that can mimic it can be found historically in the assimilation of two concepts: *simulacra* (devices that exhibit likeness) and *automata* (devices that have independence).
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## Projects
Several projects aiming to create androids that look, and, to a certain degree, speak or act like a human being have been launched or are underway.
### Japan
Japanese robotics have been leading the field since the 1970s. Waseda University initiated the WABOT project in 1967, and in 1972 completed the WABOT-1, the first android, a full-scale humanoid intelligent robot. Its limb control system allowed it to walk with the lower limbs, and to grip and transport objects with hands, using tactile sensors. Its vision system allowed it to measure distances and directions to objects using external receptors, artificial eyes and ears. And its conversation system allowed it to communicate with a person in Japanese, with an artificial mouth.
In 1984, WABOT-2 was revealed, and made a number of improvements. It was capable of playing the organ. Wabot-2 had ten fingers and two feet, and was able to read a score of music. It was also able to accompany a person. In 1986, Honda began its humanoid research and development program, to create humanoid robots capable of interacting successfully with humans.
The Intelligent Robotics Lab, directed by Hiroshi Ishiguro at Osaka University, and the Kokoro company demonstrated the Actroid at Expo 2005 in Aichi Prefecture, Japan and released the Telenoid R1 in 2010. In 2006, Kokoro developed a new *DER 2* android. The height of the human body part of DER2 is 165 cm. There are 47 mobile points. DER2 can not only change its expression but also move its hands and feet and twist its body. The \"air servosystem\" which Kokoro developed originally is used for the actuator. As a result of having an actuator controlled precisely with air pressure via a servosystem, the movement is very fluid and there is very little noise. DER2 realized a slimmer body than that of the former version by using a smaller cylinder. Outwardly DER2 has a more beautiful proportion. Compared to the previous model, DER2 has thinner arms and a wider repertoire of expressions. Once programmed, it is able to choreograph its motions and gestures with its voice.
The Intelligent Mechatronics Lab, directed by Hiroshi Kobayashi at the Tokyo University of Science, has developed an android head called *Saya*, which was exhibited at Robodex 2002 in Yokohama, Japan. There are several other initiatives around the world involving humanoid research and development at this time, which will hopefully introduce a broader spectrum of realized technology in the near future. Now Saya is *working* at the Science University of Tokyo as a guide.
The Waseda University (Japan) and NTT docomo\'s manufacturers have succeeded in creating a shape-shifting robot *WD-2*. It is capable of changing its face. At first, the creators decided the positions of the necessary points to express the outline, eyes, nose, and so on of a certain person. The robot expresses its face by moving all points to the decided positions, they say. The first version of the robot was first developed back in 2003. After that, a year later, they made a couple of major improvements to the design. The robot features an elastic mask made from the average head dummy. It uses a driving system with a 3DOF unit. The WD-2 robot can change its facial features by activating specific facial points on a mask, with each point possessing three degrees of freedom. This one has 17 facial points, for a total of 56 degrees of freedom. As for the materials they used, the WD-2\'s mask is fabricated with a highly elastic material called Septom, with bits of steel wool mixed in for added strength. Other technical features reveal a shaft driven behind the mask at the desired facial point, driven by a DC motor with a simple pulley and a slide screw. Apparently, the researchers can also modify the shape of the mask based on actual human faces. To \"copy\" a face, they need only a 3D scanner to determine the locations of an individual\'s 17 facial points. After that, they are then driven into position using a laptop and 56 motor control boards. In addition, the researchers also mention that the shifting robot can even display an individual\'s hair style and skin color if a photo of their face is projected onto the 3D Mask.
### Singapore
Prof Nadia Thalmann, a Nanyang Technological University scientist, directed efforts of the Institute for Media Innovation along with the School of Computer Engineering in the development of a social robot, Nadine. Nadine is powered by software similar to Apple\'s Siri or Microsoft\'s Cortana. Nadine may become a personal assistant in offices and homes in future, or she may become a companion for the young and the elderly.
Assoc Prof Gerald Seet from the School of Mechanical & Aerospace Engineering and the BeingThere Centre led a three-year R&D development in tele-presence robotics, creating EDGAR. A remote user can control EDGAR with the user\'s face and expressions displayed on the robot\'s face in real time. The robot also mimics their upper body movements.
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## Projects
### South Korea {#south_korea}
KITECH researched and developed EveR-1, an android interpersonal communications model capable of emulating human emotional expression via facial \"musculature\" and capable of rudimentary conversation, having a vocabulary of around 400 words. She is `{{nowrap|160 cm}}`{=mediawiki} tall and weighs `{{nowrap|50 kg}}`{=mediawiki}, matching the average figure of a Korean woman in her twenties. EveR-1\'s name derives from the Biblical Eve, plus the letter *r* for *robot*. EveR-1\'s advanced computing processing power enables speech recognition and vocal synthesis, at the same time processing lip synchronization and visual recognition by 90-degree micro-CCD cameras with face recognition technology. An independent microchip inside her artificial brain handles gesture expression, body coordination, and emotion expression. Her whole body is made of highly advanced synthetic jelly silicon and with 60 artificial joints in her face, neck, and lower body; she is able to demonstrate realistic facial expressions and sing while simultaneously dancing. In South Korea, the Ministry of Information and Communication had an ambitious plan to put a robot in every household by 2020. Several robot cities have been planned for the country: the first will be built in 2016 at a cost of 500 billion won (US\$440 million), of which 50 billion is direct government investment. The new robot city will feature research and development centers for manufacturers and part suppliers, as well as exhibition halls and a stadium for robot competitions. The country\'s new Robotics Ethics Charter will establish ground rules and laws for human interaction with robots in the future, setting standards for robotics users and manufacturers, as well as guidelines on ethical standards to be programmed into robots to prevent human abuse of robots and vice versa.
### United States {#united_states}
Walt Disney and a staff of Imagineers created Great Moments with Mr. Lincoln that debuted at the 1964 New York World\'s Fair.
Dr. William Barry, an Education Futurist and former visiting West Point Professor of Philosophy and Ethical Reasoning at the United States Military Academy, created an AI android character named \"Maria Bot\". This Interface AI android was named after the infamous fictional robot Maria in the 1927 film *Metropolis*, as a well-behaved distant relative. Maria Bot is the first AI Android Teaching Assistant at the university level. Maria Bot has appeared as a keynote speaker as a duo with Barry for a TEDx talk in Everett, Washington in February 2020.
Resembling a human from the shoulders up, Maria Bot is a virtual being android that has complex facial expressions and head movement and engages in conversation about a variety of subjects. She uses AI to process and synthesize information to make her own decisions on how to talk and engage. She collects data through conversations, direct data inputs such as books or articles, and through internet sources.
Maria Bot was built by an international high-tech company for Barry to help improve education quality and eliminate education poverty. Maria Bot is designed to create new ways for students to engage and discuss ethical issues raised by the increasing presence of robots and artificial intelligence. Barry also uses Maria Bot to demonstrate that programming a robot with life-affirming, ethical framework makes them more likely to help humans to do the same.
Maria Bot is an ambassador robot for good and ethical AI technology.
Hanson Robotics, Inc., of Texas and KAIST produced an android portrait of Albert Einstein, using Hanson\'s facial android technology mounted on KAIST\'s life-size walking bipedal robot body. This Einstein android, also called \"Albert Hubo\", thus represents the first full-body walking android in history. Hanson Robotics, the FedEx Institute of Technology, and the University of Texas at Arlington also developed the android portrait of sci-fi author Philip K. Dick (creator of *Do Androids Dream of Electric Sheep?*, the basis for the film *Blade Runner*), with full conversational capabilities that incorporated thousands of pages of the author\'s works. In 2005, the PKD android won a first-place artificial intelligence award from AAAI.
### China
On April 19, 2025, 21 humanoid robots participated along with 12,000 human runners in a half-marathon in Beijing. While almost every robot fell down and had overheating problems, and the robots were continuously being controlled by human handlers accompanying them, six of the robots did reach the finish line. Two of them, Tiangong Ultra by Chinese robotics company UBTech, and N2 by Chinese company Noetix Robotics, which took first and second place respectively among robots in the race, stood out for their consistent (albeit slow) pace.
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## Use in fiction {#use_in_fiction}
Androids are a staple of science fiction. Isaac Asimov pioneered the fictionalization of the science of robotics and artificial intelligence, notably in his 1950s series *I, Robot*. One thing common to most fictional androids is that the real-life technological challenges associated with creating thoroughly human-like robots --- such as the creation of strong artificial intelligence---are assumed to have been solved. Fictional androids are often depicted as mentally and physically equal or superior to humans---moving, thinking and speaking as fluidly as them.
The tension between the nonhuman substance and the human appearance---or even human ambitions---of androids is the dramatic impetus behind most of their fictional depictions. Some android heroes seek, like Pinocchio, to become human, as in the film *Bicentennial Man*, or Data in *Star Trek: The Next Generation*. Others, as in the film *Westworld*, rebel against abuse by careless humans. Android hunter Deckard in *Do Androids Dream of Electric Sheep?* and its film adaptation *Blade Runner* discovers that his targets appear to be, in some ways, more \"human\" than he is. The sequel *Blade Runner 2049* involves android hunter K, himself an android, discovering the same thing. Android stories, therefore, are not essentially stories \"about\" androids; they are stories about the human condition and what it means to be human.
One aspect of writing about the meaning of humanity is to use discrimination against androids as a mechanism for exploring racism in society, as in *Blade Runner*. Perhaps the clearest example of this is John Brunner\'s 1968 novel *Into the Slave Nebula*, where the blue-skinned android slaves are explicitly shown to be fully human. More recently, the androids Bishop and Annalee Call in the films *Aliens* and *Alien Resurrection* are used as vehicles for exploring how humans deal with the presence of an \"Other\". The 2018 video game *Detroit: Become Human* also explores how androids are treated as second class citizens in a near future society.
Female androids, or \"gynoids\", are often seen in science fiction, and can be viewed as a continuation of the long tradition of men attempting to create the stereotypical \"perfect woman\". Examples include the Greek myth of *Pygmalion* and the female robot Maria in Fritz Lang\'s *Metropolis*. Some gynoids, like Pris in *Blade Runner*, are designed as sex-objects, with the intent of \"pleasing men\'s violent sexual desires\", or as submissive, servile companions, such as in *The Stepford Wives*. Fiction about gynoids has therefore been described as reinforcing \"essentialist ideas of femininity\", although others have suggested that the treatment of androids is a way of exploring racism and misogyny in society.
The 2015 Japanese film *Sayonara*, starring Geminoid F, was promoted as \"the first movie to feature an android performing opposite a human actor\".
The 2023 Dutch film *I\'m Not a Robot* won the Academy Award for Best Live Action Short Film in 2025
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List of anthropologists
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***Algorithms*** is a monthly peer-reviewed open-access scientific journal of mathematics, covering design, analysis, and experiments on algorithms. The journal is published by MDPI and was established in 2008. The founding editor-in-chief was Kazuo Iwama (Kyoto University). From May 2014 to September 2019, the editor-in-chief was Henning Fernau (Universität Trier). The current editor-in-chief is Frank Werner (Otto-von-Guericke-Universität Magdeburg).
## Abstracting and indexing {#abstracting_and_indexing}
According to the *Journal Citation Reports*, the journal has a 2022 impact factor of 2.3. The journal is abstracted and indexed in: `{{columns-list|colwidth=30em|
*[[Chemical Abstracts Service]]<ref name=CASSI>{{cite web |url=http://cassi.cas.org/search.jsp |title=CAS Source Index |publisher=[[American Chemical Society]] |work=[[Chemical Abstracts Service]] |access-date=30 July 2018 |archive-url=https://wayback.archive-it.org/all/20100211180645/http://cassi.cas.org/ |archive-date=11 February 2010 |url-status=dead |df=dmy-all }}</ref>
*[[Ei Compendex]]<ref name=Compendex>{{cite web |url=http://www.elsevier.com/online-tools/engineering-village/contentdatabase-overview |title=Content/Database Overview - Compendex Source List |publisher=[[Elsevier]] |work=Engineering Village |access-date=30 July 2018}}</ref>
*[[Emerging Sources Citation Index]]<ref name=ISI>{{cite web |url=http://mjl.clarivate.com/ |title=Master Journal List |publisher=[[Clarivate Analytics]] |work=Intellectual Property & Science |access-date=30 July 2018}}</ref>
*[[Inspec]]<ref name=Inspec>{{cite web |url=http://www.theiet.org/resources/inspec/support/docs/loj.cfm?type=pdf |title=Inspec list of journals |publisher=[[Institution of Engineering and Technology (professional society)|Institution of Engineering and Technology]] |work=Inspec |access-date=30 July 2018}}</ref>
*[[MathSciNet]]
*[[Scopus]]<ref name=Scopus>{{cite web |url=https://www.scopus.com/sourceid/21100199795 |title=Source details: Algorithms |publisher=[[Elsevier]] |work=Scopus preview |access-date=30 July 2018}}</ref>
*[[zbMATH Open]] (2008–2019).<ref name=MATH>{{cite web |url=https://zbmath
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Algorithms (journal)
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