Element Abundance in Earth's Crust 28 1 The data above is from Arnett, and the elements are listed in descending order of the atom fraction in the solar system. The percent by mass in the solar system is the mass fraction in parts per million with the decimal point shifted left four places, e.g. hydrogen is 705,700 parts per million in mass and 70.57% by mass. As the lightest atom, it is 91% by number. Since specific isotopes are tabulated here, the percentages would differ slightly if all isotopes of each element are tabulated. References: Chemical Elements of the Human Body | ASU - Ask A Biologist Ask A Biologist Atoms & Life show/hide words to know Element: in chemistry a substance that cannot be broken down (separated) by a chemical process... more Trace: a quantity of something in extremely small amounts... more What Elements Are Found in the Human Body? There are 92 elements that occur naturally on Earth. For living things, only 11 of these elements are found in larger than trace quantities. Any amount 0.01% or less is considered a trace element.

For vertebrates, such as humans, there are two additional elements that occur in larger than trace amounts these are Iodine and Iron. The periodic table of elements below is color coded to show the elements found in the human body. The Top Four Elements Found in the Human Body Of the elements found in the human body, four of them make up the largest percentage of our body weight (96.2%). The four elements are oxygen, hydrogen, carbon, nitrogen. Before you start thinking we should float away with all the oxygen, hydrogen, and nitrogen atoms, remember that the oxgen molecules are mainly part of the water in our body (H2O). In fact, over half of the human body is made up of water (50-70%). Hydrogen»the essentials [WebElements Periodic Table] Element News Hydrogen: the essentials Note that while hydrogen is normally shown at the top of the Group 1 elements in the periodic table, the term "alkaline metal" refers to the Group 1 elements from lithium downwards and not hydrogen. Hydrogen is the lightest element. It is by far the most abundant element in the universe and makes up about about 90% of the universe by weight.

It is also the most abundant element in the earth's sun. Hydrogen as water (H2O) is absolutely essential to life and it is present in all organic compounds. Hydrogen is the lightest gas. Hydrogen gas was used in lighter-than-air balloons for transport but is far too dangerous because of the fire risk (Hindenburg). It burns in air to form only water as waste product and if hydrogen could be made on sufficient scale from other than fossil fuels then there might be a possibility of a hydrogen economy. CAS Registry ID : 1333-74-0 Hydrogen: historical information Hydrogen was discovered by Henry Cavendish in 1766 at London, England. Origin of name : from the Greek words "hydro" and "genes" meaning "water" and "generator". Robert Boyle (1627-1691; English chemist and physicist) published a paper ("New experiments touching the relation betwixt flame and air") in 1671 in which he described the reaction between iron filings and dilute acids which results in the evolution of gaseous hydrogen ("inflammable solution of Mars" [iron]).

However it was only much later that it was recognized as an element by Henry Cavendish (1731-1810; an English chemist and physicist who also independently discovered nitrogen) in 1766 when he collected it over mercury and described it as "inflammable air from metals". Cavendish described accurately hydrogen's properties but thought erroneously that the gas originated from the metal rather than from the acid. Hydrogen was named by Lavoisier. Deuterium gas (2H2, often written D2), made up from deuterium, a heavy isotope of hydrogen, was discovered in 1931 by Harold Urey, a professor of chemistry at Chicago and California (both USA). Sometime prior to the autumn of 1803, the Englishman John Dalton was able to explain the results of some of his studies by assuming that matter is composed of atoms and that all samples of any given compound consist of the same combination of these atoms. Dalton also noted that in series of compounds, the ratios of the masses of the second element that combine with a given weight of the first element can be reduced to small whole numbers (the law of multiple proportions).

This was further evidence for atoms. Dalton's theory of atoms was published by Thomas Thomson in the 3rd edition of his System of Chemistry in 1807 and in a paper about strontium oxalates published in the Philosophical Transactions. Dalton published these ideas himself in the following year in the New System of Chemical Philosophy. The symbol used by Dalton for hydrogen is shown below. [See History of Chemistry, Sir Edward Thorpe, volume 1, Watts & Co, London, 1914.] In 1839 a British scientist Sir William Robert Grove carried out experiments on electrolysis. He used electricity to split water into hydrogen and oxygen. He then argued one should be able to reverse the electrolysis and so generate electricity from the reaction of oxygen with hydrogen. He enclosed platinum strips in separate sealed bottles, one containing hydrogen and one oxygen. When the containers were immersed in dilute sulphuric acid a current indeed flowed between the two electrodes and water was formed in the gas bottles. He linked several of these devices in series to increase the voltage produced in a gas battery. Later the term fuel cell was used by the chemists Ludwig Mond and Charles Langer.

In 1932 Dr Francis Thomas Bacon, an engineer at Cambridge University in the UK, worked further on designs of Mond and Langer. He replaced the platinum electrodes with less expensive nickel gauze and substituted the sulphuric acid electrolyte for alkaline potassium hydroxide (less corrosive to the electrodes). This was in essence the first alkaline fuel cell (AFC) and was called the Bacon Cell. It took Bacon another 27 years to demonstrate a machine capable of producing 5 kW of power, enough to power a welding machine. At about the same time the first fuel cell powered vehicle was demonstrated. Much later fuel cells were by NASA in the 1960s for the Apollo space missions. Fuel cells have been used for more than 100 missions in NASA spacecraft. Fuel cells are also used in submarines. The lifting agent for the ill fated Hindenberg ballooon was hydrogen rather than the safer helium. The image below is the scene probably in a way you have not seen it before.

This is a "ray-traced" image reproduced with the permission of Johannes Ewers , the artist, who won first place with this image in the March/April 1999 Internet Raytracing Competition . For details of ray-tracing you can't beat the POV-Ray site. Hydrogen around us Read more » Hydrogen makes up two of the three atoms in water and water is absolutely essential to life. Hydrogen is present in all organic compounds. A form of water in which both hydrogen atoms are replaced by deuterium (2H, or D) is called "heavy water" (D2O) and is toxic to mammals. Some bacteria are known to metabolise molecular hydrogen (H2). H2 gas is present in the earth's atmosphere in very small quantities, but is present to a far greater extent chemically bound as water (H2O) Water is a constituent of many minerals. Hydrogen is the lightest element and is by far the most abundant element in the universe, making up about about 90% of the atoms or 75% of the mass, of the universe. Hydrogen is a major constituent of the the sun and most stars.

The sun burns by a number of nuclear processes but mainly through the fusion of hydrogen nuclei into helium nuclei. Hydrogen is a major component of the planet Jupiter. In the planet's interior the pressure is probably so great that solid molecular hydrogen is converted into solid metallic hydrogen. Abundances for hydrogen in a number of different environments. More abundance data » Location Second ionisation energy : (no data) kJ mol‑1 Isolation Isolation : in the laboratory, small amounts of hydrogen gas may be made by the reaction of calcium hydride with water. CaH2 + 2H2O → Ca(OH)2 + 2H2 This is quite efficient in the sense that 50% of the hydrogen produced comes from water. Another very convenient laboratory scale experiment follows Boyle's early synthesis, the reaction of iron filings with dilute sulphuric acid. Fe + H2SO4 → FeSO4 + H2 There are many industrial methods for the production of hydrogen and that used will depend upon local factors such as the quantity required and the raw materials to hand. Two processes in use involve heating coke with steam in the water gas shift reaction or hydrocarbons such as methane with steam.

CH4 + H2O (1100°C) → CO + 3H2 C(coke) + H2O (1000°C) → CO + H2 In both these cases, further hydrogen may be made by passing the CO and steam over hot (400°C) iron oxide or cobalt oxide. CO + H2O → CO2 + H2 Read more » The Hydrogen isotope H-2, also known as deuterium, is used in a variety of applications. Deuterium is used extensively in organic chemistry in order to study chemical reactions. It is also used in vitamin research. Deuterium in the form of H2O, known as heavy water, is used as a moderator in CANDU nuclear reactors, in NMR studies and in studies into human metabolism. Heavy water is also applied in the Sudbury Neutrino Observatory where it is used to study the behavior of neutrinos. What Is Our Sun Made Of? What Is Our Sun Made Of? By SPACE | March 1, 2012 12:04pm ET MORE This snapshot from NASA's Solar Dynamics Observatory shows a stunning prominence associated with a Sept.

8, 2010 solar flare. Credit: NASA/SDO The sun is mostly composed of the elements hydrogen (H) and helium (He). By mass the composition of the sun is 75 percent hydrogen and 25 percent helium. Various metals make up less than 0.1 percent of the mass of the sun. The temperature of the sun’s surface is about 10,340 degrees Fahrenheit (5,726 degrees Celsius). SpaceKids on SPACE.com provides simple, straightforward answers to really big cosmic questions. See more SpaceKids questions Planets of the Solar System The Jovian Planets The Sun and the five largest planets of the solar system (to scale). The Earth is the tiny dot between Jupiter and the Sun. (Source: NASA ) By far most of the solar system's mass is in the Sun itself: somewhere between 99.8 and 99.9 percent. The rest is split between the planets and their satellites, and the comets and asteroids and the dust and gas surrounding our star. Seen from afar (on the scale of distances between stars) the presence of the solar system would not be obvious. We would simply see a normal-looking star.

Perhaps we would pick up the presence of Jupiter, which makes up two thirds or so of the solar system outside of the Sun, by mass. Jupiter (Source: NASA ) Because Jupiter has most of the mass of what the Sun left over, we can think of the solar system as a double star with very unequal partners. The little guy (Jupiter) is 1/1000 the mass of the big one (Sun) and doesn't have enough mass to produce the pressure necessary for ignition at its center. It does have pretty much the same composition as the Sun ( hydrogen and helium in solar proportions, along with some carbon, nitrogen and oxygen). Also, it does radiate heat � almost as much again as it receives from the Sun. This heat is released by the radioactive decay of elements within the planet and (perhaps) from gravitational effects, as the heavier elements move toward the center. (Earth also radiates its own heat, but it is negligible compared with energy of solar origin.) Jupiter and Saturn together make up more than 90 percent of the mass of all planets. The bulk of their mass is in hydrogen and helium , as mentioned.

Also, the compounds ammonia (nitrogen hydride), methane (carbon hydride) and water (oxygen hydride) are seen in their atmospheres . These are the most obvious combinations of the four most common elements (besides helium), and the fact that they are abundant reflects the relatively low temperature of the outer atmosphere of the two main planets. (Helium, as a noble gas , does not combine with other elements.) The next two largest planets are Uranus (discovered 1781, by William Herschel) and Neptune (discovered 1846, by Johannes Galle; see also Adams and Leverrier). The two are roughly equal in size and mass, at about five percent of Jupiter and less than a fifth of Saturn. The composition of Uranus is much like that of Jupiter and Saturn. Also, like those two giants, it has (wispy) rings and lots of satellites. Apparently, Neptune was first seen by Galileo (he sketched it when observing Jupiter in 1613) but he did not recognize its nature as a planet. Neptune has a composition much like the other "Jovian" planets, but has somewhat greater density.

It too has debris and satellites encircling it. Pluto, the outermost planet, is roughly the size of the Moon and consists of dusty ice, much like a comet . It has a large companion, "Charon". Pluto: The brown color of the planet is thought to be due to frozen methane deposits. No spacecraft from Earth has as yet visited Pluto. This image was taken with an Earth-based telescope. (Source: NASA ) Four Elements: Earth, Water, Air, Fire - Noteworthy Scientist: George Gabriel Stokes - Fabulous Facts Earth, Water, Air, and Fire: The Four States of Matter The ancient Greeks believed that there were four elements that everything was made up of: earth, water, air, and fire. This theory was suggested around 450 BC, and it was later supported and added to by Aristotle. (Aristotle also suggested that there was a fifth element, aether, because it seemed strange that the stars would be made out of earthly elements.

He would be surprised to learn that they are in fact made up of many elements found on earth, and are so hot they could be said to be on fire all the time!) The idea that these four elements - earth, water, air, and fire - made up all matter was the cornerstone of philosophy, science, and medicine for two thousand years. The elements were "pure" but could not be found in that state on earth. Every visible thing was made up of some combination of earth, water, air, and fire. The four elements were even used to described the four temperaments a person could have, and Hippocrates used the four elements to describe the four "humors" found in the body. These theories stated that the temperaments and humors needed to be in balance with each other in order for a person to be well both mentally and physically. While we do know now that these previous theories are false, in a way the four elements do align with the four states of matter that modern science has agreed on: solid (earth), liquid (water), gas (air), and plasma (fire).

Although the Greeks believed that the four elements were unchanging in nature, everything was made up of different elements, which were held together or pushed apart by forces of attraction and repulsion, causing substances to appear to change. This is similar to what really happens with elements and all molecules at an atomic level. Matter is anything that has mass and volume and is made up of atoms, which are the smallest particles of matter. Bonding occurs among atoms to make larger molecules. (Click here to learn more about bonding.) Mass is how much matter is in an object whereas volume is how much space the object takes up. How atoms are arranged in an object determines whether it is a solid, liquid, gas, or plasma. In a solid, the atoms are packed closely together in an ordered pattern and cannot move, giving a solid a definite volume and shape. Examples of solids include rocks, wood, metal, and ice. In a liquid, the atoms are close together but can move around each other. This allows a liquid to take the shape of whatever container it is placed in. Examples of liquids include room temperature water, room temperature mercury, and hot lava (molten rock). In a gas, there is more space between atoms.

The atoms can move so freely that if the gas is not trapped in a container, the atoms will diffuse and spread throughout the atmosphere. Examples of gases are oxygen and nitrogen (in the air we breathe), helium, and steam (water vapor). In a plasma, the atoms are spaced similarly to gas except there is so much energy in a plasma, the atoms actually split into smaller pieces. Plasmas are able to carry an electrical current and generate magnetic fields. Examples of plasmas include lightning, solar wind, the sun, fluorescent lights, and neon signs. Temperature plays an important role in how the atoms are aligned in a substance. As a general rule of thumb, the colder the matter is, the closer the atoms are to each other, and the warmer the matter is, the farther the atoms are apart. Of course, the temperature at which a matter is a solid or a liquid depends on what substance the matter is made of. For example, water at room temperature is a liquid whereas a rock at room temperature is solid. Earth, Water, Air, and Fire: Active Role in Everyday Life The earth is full of a wide variety of rocks and minerals which provides the soil to grow vegetation and support life.

The two most common elements in the earth's crust are oxygen (46%) and silicon (28%). Because of this, the most abundant mineral in the earth's crust is silica (silicon dioxide). More commonly known as sand, silica is a major component of glass. How can glass be made out of sand? Interestingly, when silica is heated, it melts and becomes glass, hardening as it cools. Rich deposits of metal ores are found throughout the earth's crust. While these metals are used in the production of machinery, tools, buildings, and weapons, straight out of the earth these metals are pretty useless. Fire is used to heat, refine, and shape metal so that machines, hammers, and support beams can be made from it. It is easy to think of the earth as being solid dirt through and through, but in reality it is made up of several layers. While many of these layers are solid, the layer that surrounds the core is called the liquid outer core. It is so hot inside the earth that the rock at this layer has actually melted. The solid inner core is just as hot as the liquid layer surrounding it, but the pressure on the inner core is so great that scientists believe it is "pressed" into a solid.

The chemical formula of water is H20, meaning it is made of two hydrogen atoms bonded to one oxygen atom. The hydrogen atoms each attach to one side of the oxygen atom and have a positive charge whereas the oxygen atom has a negative charge. This polarizes the water molecule, much like a magnet, giving a water molecule positive and negative ends. Since opposite charges attract, water molecules tend to "stick" together. This gives water surface tension and allows objects, such as paperclips, to float on it. While it can't dissolve everything, water is known as the universal solvent because it can dissolve more substances than any other liquid. It can dissolve salt, sugar, acids, alkalis, some gases, and organic material. Water traveling through your body or through the ground takes chemicals, minerals, and nutrients with it. Water's ability to dissolve substances helps keep the planet healthy. For more than a century, the burning of fossil fuels has pumped large amounts of carbon dioxide (CO2) into the atmosphere. The water in oceans have absorbed about half of this CO2 by dissolving the gas from the air and processing it by sea vegetation. Water has a high specific heat index, meaning that it takes a lot of energy to change its temperature.

This is essential for life to survive on a planet. The abundance of water on the earth keeps the planet in a very short but comfortable temperature range. The average surface temperature of the earth is 59 ° F with the highest recorded temperature 135.9 ° F and the lowest recorded temperature -128.6 ° F. To compare, it would seem logical that Mercury, the closest planet to the sun, would stay really warm on all surfaces of the planet, regardless if it was facing the sun or not. However, while the surface facing the sun does reach very warm temperatures (up to 800 ° F), the surfacing facing away from the sun drops to a chilly -280 ° F. Mercury's lack of water is responsible for this drastic temperature change because the dry material that makes up its surface cannot hold heat like water does. To experience for yourself how well water does keep temperature from drastic fluctuations, pay attention to the change between daytime and nighttime temperatures the next time you visit a maritime (near the ocean) or desert climate. You'll probably notice there is little to no temperature change near the ocean, whereas in the desert there is a significant change in daytime and nighttime temperatures.

This high specific heat index also helps water put out fire by cooling the fuel surfaces that the fire is burning, removing the heat needed for the fire to burn. Water also smothers a fire by preventing it from getting the oxygen it needs to burn. Air was considered a "pure" element, but in fact the air that's all around us is made up of a variety of gases: primarily nitrogen and oxygen, with almost 1% argon and even smaller amounts of carbon dioxide and other elements such as krypton and helium. The composition of air is just right for life on Earth, though. We use a lot of the oxygen we get from the air, then breathe out carbon dioxide - which plants need to manufacture their food through photosynthesis. Plants in turn give off oxygen during photosynthesis. Although air is invisible (and most of the time we forget it is even there), it does take up space, it has volume, and it exerts pressure. This can be seen when you take an "empty" glass, turn it upside down, and try to push it down to the bottom of a sink full of water. If the glass was truly empty, the water would easily fill the inside of the glass.

But air is in there, and only a small amount of water can enter the glass. The air in the glass was compressed, giving the water some space that was previously occupied with air. It is a good thing that air fills empty space because air all around us actually presses down on us all the time. We would collapse under the weight of the air, except air is also inside us and exerts pressure that balances out the pressure exerted by the outside air. How does fire work? It's closely linked to air. Fire needs three things in order to exist: oxygen, fuel, and heat. The intensity of a fire varies because it is dependent on the oxygen, fuel, and heat available to it. When all three of these things are in a controlled situation, such as in candles or a campfire, fires are considered helpful. But when one or more of these things are not controlled, such as in a wildfire or a burning building, fires can easily become very dangerous. To extinguish a fire, the oxygen, fuel, or heat needs to be removed. "Smothering" a fire by placing a blanket or dirt on it works because the fire goes out without oxygen.

The earth provides an abundance of fuel in the form of wood and fossil fuels such as coal. When the fuel is removed, the fire has nothing left to burn and is extinguished. Water often serves as an effective cooling source by removing the heat from a fire. This is seen when hot lava from an erupting volcano enters the ocean or when a bucket of water is dumped on a campfire. Fire creates light, heat, and smoke by a rapid chemical reaction called combustion. Smoke is the result of the incomplete combustion (burning) of a fuel. Particles that were not burned become suspended in the air. Smoke is often dangerous because it contains harmful gases that can poison a person who inhales too much smoke. You might be surprised to know that our bodies also use "combustion" to produce energy from oxygen and food through metabolic processes. We need a steady supply of oxygen to keep our bodies functioning normally; if there's too little oxygen in the air, we'll suffocate. At the same time, we can be thankful there's not more oxygen in the air, or the chemical reactions in our bodies would speed up, causing us to soon "crash and burn"!

Too much oxygen in the air would also increase the risk of fires on the earth. Since nitrogen and argon are not very reactive, air is pretty safe for us. Make a Fire Extinguisher In order to put out a fire, one of three things must be removed from it: heat, fuel, or oxygen. Knowing this, firefighters don't always use water to put out a fire. What You Need: 1/2 tablespoon of baking soda Tea light candle What You Do: Light the candle. Pour the vinegar into the bottle and add the baking soda. (You may want to use a funnel.) The mixture should fizz. Hold the bottle sideways over the lighted candle, making sure no liquid escapes. What happens to the flame? What Happened: The baking soda and vinegar react to make carbon dioxide, a gas that is heavier than oxygen. As it "pours" out of the bottle, it pushes the lighter oxygen away from the candle. The fire, now deprived of oxygen, can no longer burn. Traveling Nutrients Water is often called the Universal Solvent because it can dissolve more substances than any other liquid, often carrying these dissolved particles with it.

When water travels through soil, nutrients (food) and dissolved particles travel with the water to be deposited somewhere else. Here is an experiment to visually demonstrate how this process happens. What You Need: Measuring cup What You Do: Mix the dry soil and tempera paint thoroughly. Place the funnel in the jar and place the coffee filter in the funnel. Pour the soil mixture into the funnel. Slowly pour 1/2 cup water into the funnel, watching as the water runs out of the funnel into the jar. Notice the color of the water. Remove the funnel from the jar and pour the water into a cup or container. Replace the funnel over the jar, with the coffee filter full of sand still in place. Repeat steps 2 and 3 with a fresh 1/2 cup of water several times, saving the water in a new cup after each pouring. What Happens: When the first half cup of water went through the soil, the water that came out was very dark blue in color. However, each subsequent cup that went through the soil mixture came out lighter and lighter. Eventually, the water traveling through the soil came out clear in the jar. How many half cups of water did it take for the water to run clear?

The tempura paint in this experiment represents the nutrients and dissolved particles found in the soil. Water is a very efficient transporter of particles as evidenced by the color of water as it was poured through the soil. The soil started with a relatively high amount of nutrients and particles in it - the tempura paint. The water flowing through the soil was able to pick up a large proportion of the "nutrients" and carry them with it through the funnel. Each subsequent pouring of water picked up more nutrients. With each pouring, the remaining nutrients became less and less until the water ran clear and there were no more nutrients left to travel with the water. Noteworthy Scientist: George Gabriel Stokes, 1819-1903 George Gabriel Stokes was an accomplished British mathematician in the 19th Century, but throughout his career, he emphasized the importance of experimentation and problem solving rather than focusing solely on mathematics. By experimenting and applying mathematics to physics, Stokes came up with a law that describes the movement of a solid through a liquid or a gas. Known as Stoke's Law, this law of viscosity established the science of hydrodynamics. Stoke's Law explains cloud motion, wave motion, and the resistance of water to ship movement.

Most of Stoke's work revolved around waves (sound, light, and water) and how they move through various mediums, such as water and gas. He experimented with how wind affects the intensity of a sound and how the intensity is influenced by the type of gas the sound waves travel through. He named and explained fluorescence and investigated the wave theory of light. He also worked on understanding the different colored bands that could be seen in a spectrum and made significant contributions to what we know about light and optics. Stokes is often compared to Sir Isaac Newton because there are numerous parallels between Stoke's life and Newton's life: both had breakthrough discoveries, developed laws of motion, investigated light and optics, held the same prestigious Lucasian Chair of Mathematics at the University of Cambridge, and served in Parliament. Fabulous Facts Most gemstones contain several elements. The exception? The diamond. It's all carbon. Which of the 50 states has never had an earthquake? North Dakota. The Earth's equatorial circumference (40,075 km) is greater than its polar circumference (40,008 km). The Earth is estimated to weigh 6.6 sextillion tons, or 5.97 x 1024 kg.

To compare, a million is a 1 with 6 zeros following it - a sextillion is a 1 with 21 zeros following it. (1,000,000,000,000,000,000,000) Water An inch of rain water is equivalent to 15 inches of dry, powdery snow. The deepest part of the ocean is 35,813 feet (10,916 meters) deep and occurs in the Mariana Trench in the Pacific Ocean. At that depth the pressure is 18,000 pounds (9172 kilograms) per square inch. The human brain is 80% water. Air 8-12 miles above the earth, rivers of air known as jet streams move above us. Several miles wide and 1-2 miles deep, these currents of air can have wind speeds as high as 250 miles per hour. To contrast, the strongest hurricanes have wind speeds between 150-200 miles per hour. Fire A bolt of lightning is about 5,000 °F (~2,800 °C).

The center of the Sun is about 27 million degrees Fahrenheit (15 million °C). Elements combined When hydrogen burns in the air, water is formed. Oxygen is the most abundant element in the Earth's crust, waters, and atmosphere (about 49.5%). Sound travels about 4 times faster in water than in air. Wind and water both cause erosion to the earth, moving large amounts of sand and rock to tear down mountains and build new structures. Clickable Periodic Table of the Elements Clickable Periodic Table of the Elements Clickable Periodic Table of the Elements Look Up Element Facts on the Interactive Periodic Table continue reading below our video 10 Best Universities in the United States How To Read the Periodic Table of the Elements Click on an element symbol to get detailed facts about each chemical element. The element symbol is a one- or two-letter abbreviation for an element's name. The integer number above the element symbol is its atomic number . The atomic number is the number of protons in every atom of that element. The number of electrons can change, forming ions , or the number of neutrons can change, forming isotopes , but the proton number defines the element. The modern periodic table orders the element by increasing atomic number.

Mendeleev's periodic table was similar, but the parts of the atom weren't known in his day, so he organized elements by increasing atomic weight. The number below the element symbol is called the atomic mass or the atomic weight . It's the sum of the mass of protons and neutrons in an atom (electrons contribute negligible mass), but you may notice it isn't the value you'd get if you assumed the atom had an equal number of protons and neutrons. The atomic weight values may be different from one periodic table to another because it's a calculated number, based on the weighted average of the natural isotopes of an element. If a new supply of an element is discovered, the isotope ratio may be different from what scientists previously believed. Then, the number may change. Note, if you have a sample of a pure isotope of an element, the atomic mass is simply the sum of the number of protons and neutrons of that isotope! Element Groups and Element Periods The periodic table gets its name because it arranges the elements according to recurring or periodic properties . The groups and periods of the table organize elements according to these trends.

Even if you didn't know anything about an element, if you knew about one of the other elements in its group or period, you could make predictions about its behavior. Groups Most periodic tables are color-coded so that you can see at a glance which elements share common properties with each other. Sometimes these clusters of elements (e.g., alkali metals, transition metals, non-metals) are called element groups, yet you'll also hear chemists refer to the columns (moving top to bottom) of the periodic table called element groups. Elements in the same column (group) have the same electron shell structure and the same number of valence electrons. Since these are the electrons that participate in chemical reactions, elements in a group tend to react similarly. The Roman numerals listed across the top of the periodic table indicate the usual number of valence electrons for an atom of an element listed below it. For example, an atom of a group VA element will typically have 5 valence electrons. Periods The rows of the periodic table are called periods. Atoms of elements in the same period have the same highest unexcited (ground state) electron energy level.

As you move down the periodic table, the number of elements in each group increases because there are more electron energy sublevels per level. Periodic Table Trends In addition to the common properties of elements in groups and periods, the chart organizes elements according to trends in ionic or atomic radius, electronegativity, ionization energy, and electron affinity. Atomic radius is half the distance between two atoms that are just touching. Ionic radius is half the distance between two atomic ions that are barely touching. Atomic radius and ionic radius increase as you move down an element group and decrease as you move across a period from left to right. Electronegativity is how easily an atom attracts electrons to form a chemical bond. The higher its value, the greater the attraction for bonding electrons. Electronegativity decreases as you move down a periodic table group and increases as you move across a period. The energy needed to remove an electron from a gaseous atom or atomic ion is its ionization energy . Ionization energy decreases moving down a group or column and increases moving from left to right across a period or row. Electron affinity is how easily an atom can accept an electron.

Except that the noble gases have practically zero electron affinity, this property generally decreases moving down a group and increases moving across a period. The Purpose of the Periodic Table The reason chemists and other scientists use the periodic table rather than some other chart of element information is because the arrangement of elements according to periodic properties helps predict properties of unfamiliar or undiscovered elements. You can use the location of an element on the periodic table to predict the types of chemical reactions it will participate in and whether or not it will form chemical bonds with other elements. Printable Periodic Tables and More Sometimes it's helpful to print out a periodic table, so you can write on it or have it with you anywhere. I've got a large collection of periodic tables you can download to use on a mobile device or print. I've also got a selection of periodic table quizzes you can take to test your understanding of how the table is organized and how to use it to get information about the elements. Untitled Document Tree Facts General Information Trees help our soil remain healthy by reducing soil erosion and by creating a soil climate suitable for microorganism to grow. There are over 23,000 different kinds of trees in the world.

A healthy tree can increase your property value by as much as 27 percent while trees with dead branches, hollow cavities and other problems can decrease your property value. Evergreen trees are green year round because they do not lose all of their leaves in one season. Most will however lose some of their oldest leaves just before they produce new leaves in the spring. Some will lose part of their leaves in the fall. A tree can absorb as much as 48 pounds of carbon dioxide per year and can sequester 1 ton of carbon dioxide by the time it reaches 40 years old. Tree leaves are composed of many colored pigments -- green chlorophyll hides them during the spring and summer growing seasons. Shorter days and cool temperatures in the fall cause the chlorophyll to break down and the other pigments to be see. Every state has an official State Tree. We do not have a national tree, however, there is a campaign to have the oak adopted as our National Tree. Arbor Day, a day site aside to plant and recognize the importance of trees, is not a national holiday. If fact the day observed varies from state to state. Tree wood is a highly organized arrangement of living, dying, and dead cells.

The beginning and growth of tall woody trees in forests may have played a key role in the extinction of the dinosaurs. Hundreds of food products (fruit, coffee, nuts, etc.) and food additives (for ice cream, chewing gum, etc.) come from trees. One large tree can lift up to 100 gallons of water out of the ground and discharge it into the air in a day. One large tree can provide a day's supply of oxygen for up to four people. Each year, one person uses wood and paper products equivalent to a 100 foot tree 18 inches in diameter. Over 5,000 products are made from trees. Trees are included in most religions. Some hold certain trees sacred; other use trees to help teach beliefs. The story goes that Buddha received his enlightment under the wisdom tree. Each year over 600,000 people travel to Macon, Georgia to see 240,000 cherry trees in bloom. The estimated revenue is over $6.5 million dollars per year.

Age/Size Trees are the largest living organism on earth: - Some coastal redwoods are over 360 feet tall - Some swamp ash trees are almost 300 feet tall - Giant seguoia trees can weigh over 2000 tons (4 million pounds) - It can take 10 minutes to walk around the crown of a giant banyon tree in Calcutta. - Monkey trees can have a crown of almost 200 feet. Trees are some of the oldest living organism on earth: - live oaks can live to be over 500 years - many giant sequoia trees are 2,500 years old - some bristlecone pines are thought to be over 5000 years old. Trees grown in city conditions often do not live as long (average 13 years less) as trees grown in their natural wooded environment. Growth Trees trap more of the sun's energy than any other group of organisms on earth -- they are in essence big batteries -- the largest on earth. Only 0.1% of the sun's energy is trapped by organisms -- trees account for 50% of all energy trapped by organism.

Almost 98% (by weight) of a tree is made up of six elements: carbon, hydrogen, oxygen, nitrogen, phosphorus and sulfur. Tree growth occurs in specialized tissues referred to as meristems. This tissue is found at the tips of leaves and shoots. Growth in diameter occurs at the vascular cambium inside the stem. If a birdhouse is hung on a tree branch, it does not move up the tree as the tree grows. Trees need food to grow but you can't buy food for them. They make their own food from sunlight, water, carbon dioxide and nutrients from the soil. Trees do not grow beyond their ability to support themselves. During periods of stress they shed leaves, flowers, fruit and/or branches. Trees do not restore and repair wood that is injured and infected -- instead they compartmentalize off the damaged tissue. New cells are not produced to replace the damaged cells. A hollow in a tree is never greater than the diameter of the tree at the time it was injured. It should not spread into the new growth that occurs after the tree was injured. A tree branch is not actually attached to the rest of the tree. It is held in place by a series of interlocking "collars".

Collars overlap and mesh to form a tight woven pattern of tissue. During periods of increased or decreased temperature, cracks may develop in the tree trunk -- referred to as frost cracks and sun cracks. Both can lead to decay. Each year trees produce an increment of new growth that covers growth from the previous year. The age of a tree can be determined by the number of growth rings. The size of the growth ring is determined in part by environmental conditions - temperature, water availability. Tree trunk cells produced in the spring are larger, have thinner walls and are lighter in color than cells produced in the summer. Bark is the protective covering of a tree. The outer bark is composed of dead cells. The bark will often split as the trunk diameter increases. Different parts of the tree grow at different times of the year. A typical pattern is for most of the foliage growth to occur in the spring, followed by trunk growth in the summer and root growth in the fall and winter. Not all trees follow the same pattern. Roots Most trees do not have a tap root. Tree roots do not grow very deep. Most tree roots are in the top 12 inches of soil. Tree roots often extend two to three times the width of the tree.

Roots do not have green chlorophyll. Roots store more starch than the trunk. Roots do not have a central pith (soft central tissue) while the trunk does. The majority of tree roots are non-woody. These root hairs grow within days of when water, temperature, and nutrients are available to promote growth. These non-woody roots only live for a few weeks. Non-woody tree roots can grow almost any time the soil is not frozen. Flowers, Seeds Almost all trees produce flowers -- some are very showy. Trees that depend on the wind for pollination have non-showy flowers. Often their flowers are muted shades of green or yellowish green. Trees can be classified as gymnosperms or angiosperms. Gymnosperms produce their seeds on the surface or tips of an appendage such as a pine cone. Angiosperms produce their seeds inside a fruit such as an acorn. Most trees are grown from seeds -- this leads to variability in the age at which they flower, the amount of flowers produced and the intensity of fall color. Ideally, trees you plant would be grown from seeds collected in a similar climate.

Seeds collected in areas with significantly different temperatures will have a different cold and heat tolerance. Most tree seeds require two growing seasons to germinate. Some tree species require a period of cold weather and others will not germinate for several years.

Question: Which element accounts for 75% of the weight of the sun?
Answer: Hydrogen