Element | Article about element by The Free Dictionary Element | Article about element by The Free Dictionary See also: Elements (table) Elements Element Symbol Atomic Number Atomic Weight1 Melting Point (Degrees Celsius) actinium Ac 89 (227) 1050. 3200. ±300 aluminum Al 13 26.98154 660.37 2467. americium Am 95 (243) 1172. 2600. ..... Click the link for more information. element, in chemistry, a substance that cannot be decomposed into simpler substances by chemical means. A substance such as a compound compound, in chemistry, a substance composed of atoms of two or more elements in chemical combination, occurring in a fixed, definite proportion and arranged in a fixed, definite structure. A compound is often represented by its chemical formula. ..... Click the link for more information. can be decomposed into its constituent elements by means of a chemical reaction, but no further simplification can be achieved.

An element can, however, be decomposed into simpler substances, such as protons and neutrons or various combinations of them, by the methods of particle physics, e.g., by bombardment of the nucleus. The Atom The smallest unit of a chemical element that has the properties of that element is called an atom atom [Gr.,=uncuttable (indivisible)], basic unit of matter; more properly, the smallest unit of a chemical element having the properties of that element. Structure of the Atom ..... Click the link for more information. . Many elements (e.g., helium) occur as single atoms. Other elements occur as molecules made up of more than one atom. Elements that ordinarily occur as diatomic molecules include hydrogen, nitrogen, oxygen, and the halogens, but oxygen also occurs as a triatomic form called ozone. Phosphorus usually occurs as a tetratomic molecule, and crystalline sulfur occurs as molecules containing eight atoms. Atomic Number and Mass Number Regardless of how many atoms the element is composed of, each atom has the same number of protons in its nucleus, and this is different from the number in the nucleus of any other element. Thus this number, called the atomic number (at. no.), defines the element.

For example, the element carbon consists of atoms all with at. no. 6, i.e., all having 6 protons in the nucleus; any atom with at. no. 6 is a carbon atom. By 2006, 117 elements were known, ranging from hydrogen with an at. no. of 1 to an as yet unnamed element (temporarily known as ununoctium ununoctium , artificially produced radioactive chemical element; symbol Uuo; at. no. 118. Scientists from the Joint Institute for Nuclear Research in Dubna, Russia, and Lawrence Livermore National Laboratory in California collaborated in the discovery of ununoctium in ..... Click the link for more information. ) with an at. no. of 118. (See the table entitled Elements Elements Element Symbol Atomic Number Atomic Weight1 Melting Point (Degrees Celsius) actinium Ac 89 (227) 1050. 3200. ±300 aluminum Al 13 26.98154 660.37 2467. americium Am 95 (243) 1172.

2600. ..... Click the link for more information. for an alphabetical list of all the elements, including their symbols, atomic numbers, atomic weights, and melting and boiling points.) The nuclei of most atoms also contain neutrons. The total number of protons and neutrons in the nucleus of an atom is called the mass number. For example, the mass number of a carbon atom with 6 protons and 6 neutrons in its nucleus is 12. Isotopes Although all atoms of an element have the same number of protons in their nuclei, they may not all have the same number of neutrons. Atoms of an element with the same mass number make up an isotope isotope , in chemistry and physics, one of two or more atoms having the same atomic number but differing in atomic weight and mass number. The concept of isotope was introduced by F. ..... Click the link for more information. of the element. All known elements have isotopes; some have more than others. Hydrogen, for example, has only 3 isotopes, while xenon has 16.

Approximately 300 naturally occurring isotopes are known, and more than 2,500 radioactive isotopes have been artificially produced (see synthetic elements synthetic elements, in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first element to be synthesized, promethium (at. no. 61), astatine (at. no. ..... Click the link for more information. ). There are 13 isotopes of carbon, having from 2 to 14 neutrons in the nucleus and therefore mass numbers from 8 to 20. Not all of the elements have stable isotopes. Some have only radioactive isotopes, which decay to form other isotopes, usually of other elements (see radioactivity radioactivity, spontaneous disintegration or decay of the nucleus of an atom by emission of particles, usually accompanied by electromagnetic radiation. The energy produced by radioactivity has important military and industrial applications. ..... Click the link for more information. ). In some cases all the isotopes of an element are very unstable, and the element is therefore not found in nature.

Only 94 of the elements are known to occur naturally on earth. Of these, 6 occur in minute amounts produced by the decay of other elements. These 6 extremely scarce elements and those that do not occur at all naturally were discovered when they were produced in the laboratory; they are often called the man-made, artificially produced, or synthetic elements synthetic elements, in chemistry, radioactive elements that were not discovered occurring in nature but as artificially produced isotopes. They are technetium (at. no. 43), which was the first element to be synthesized, promethium (at. no. 61), astatine (at. no. ..... Click the link for more information. . Atomic Mass and Atomic Weight Atoms are not very massive; a carbon atom weighs about 2 × 10−23 grams. Because atoms have so little mass, a unit much smaller than the gram is used.

In the current system (adopted in 1960–61) the unit of atomic mass, called atomic mass unit atomic mass unit or amu, in chemistry and physics, unit defined as exactly 1-12 the mass of an atom of carbon-12, the isotope of carbon with six protons and six neutrons in its nucleus. One amu is equal to approximately 1.66 × 10−24 grams. ..... Click the link for more information. (amu), is defined as exactly 1-12 the mass of an atom of carbon-12. The atomic weight atomic weight, mean (weighted average) of the masses of all the naturally occurring isotopes of a chemical element, as contrasted with atomic mass, which is the mass of any individual isotope. Although the first atomic weights were calculated at the beginning of the 19th cent. ..... Click the link for more information. of an element is the mean (weighted average) of the atomic masses of all the naturally occurring isotopes. Carbon has two principal naturally occurring isotopes, carbon-12 and carbon-13.

Carbon-12, whose mass is defined as exactly 12 amu, constitutes 98.89% of naturally occurring carbon; carbon-13, whose mass is 13.00335 amu, constitutes 1.11%. (There are also small traces of the radioactive isotope carbon-14.) The atomic weight of the element is determined by multiplying the percent abundance of each isotope by the atomic mass of the isotope, adding these products, and dividing by 100. However, isotope abundance is often determined by the medium of the source, solid, liquid, or gas, and the average atomic weight may fluctuate.

Thus, for carbon, [(98.89 × 12.000) + (1.11 × 13.00335)]/100 = 12.01115, which is the atomic weight of the element carbon in amu, but because the proportions of the isotopes vary depending on where the carbon is found, carbon's atomic weight is now expressed as an interval defined by the lower and upper bounds within which the atomic weight ranges: [12.0096; 12.0116]. Certain synthetic elements exist only momentarily in the form of a few short-lived isotopes; in such cases the concept of atomic weight cannot be applied. Properties of the Elements Properties of an element are sometimes classed as either chemical or physical. Chemical properties are usually observed in the course of a chemical reaction, while physical properties are observed by examining a sample of the pure element. The chemical properties of an element are due to the distribution of electrons around the atom's nucleus, particularly the outer, or valence, electrons; it is these electrons that are involved in chemical reactions.

A chemical reaction does not affect the atomic nucleus; the atomic number therefore remains unchanged in a chemical reaction. Some properties of an element can be observed only in a collection of atoms or molecules of the element. These properties include color, density, melting point, boiling point, and thermal and electrical conductivity. While some of these properties are due chiefly to the electronic structure of the element, others are more closely related to properties of the nucleus, e.g., mass number. The elements are sometimes grouped according to their properties. One major classification of the elements is as metals metal, chemical element displaying certain properties by which it is normally distinguished from a nonmetal, notably its metallic luster, the capacity to lose electrons and form a positive ion, and the ability to conduct heat and electricity. ..... Click the link for more information. , nonmetals nonmetal, chemical element possessing certain properties by which it is distinguished from a metal. In general, this distinction is drawn on the basis that a nonmetal tends to accept electrons and form negative ions and that its oxide is acidic. ..... Click the link for more information. , and metalloids.

Elements with very similar chemical properties are often referred to as families; some families of elements include the halogens, the inert gases, and the alkali metals. In the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled ..... Click the link for more information. the elements are arranged in order of increasing atomic weight in such a way that the elements in any column have similar properties. Official Symbols and Names for the Elements Each element is assigned an official symbol by the International Union of Pure and Applied Chemistry (IUPAC). For example, the symbol for carbon is C, and the symbol for silver is Ag [Lat. argentum = silver]. There are several ways of designating an isotope. One designation consists of the name or symbol of the element followed by a hyphen and the mass number of the isotope; thus the isotope of carbon with mass number 12 can be designated carbon-12 or C-12.

The mass number is often written as a superscript, e.g., C12; sometimes the atomic number is written as a subscript preceding the symbol, e.g., 6C12. The IUPAC rules for nomenclature of inorganic chemistry state that the subscript atomic number and superscript mass number should both precede the symbol, e.g., 126C. Many isotopes were given special names and symbols when they were first discovered in natural radioactive decay series (e.g., uranium-235 was called actinouranium and represented by the symbol AcU). This practice is discouraged in the modern nomenclature except in the case of hydrogen. The isotopes hydrogen-2 and hydrogen-3 are usually called deuterium and tritium, respectively. Hydrogen-1, the most abundant isotope, has the name protium but is usually simply called hydrogen. Newly discovered elements that have been synthesized by one laboratory and not yet confirmed by a second are given a provisional name based on Greek and Latin roots; when the discovery is confirmed, the laboratory that first made it may suggest a name for the element. The Elements through the Ages Some elements have been known since antiquity.

Gold ornaments from the Neolithic period have been discovered. Gold, iron, copper, lead, silver, and tin were used in Egypt and Mesopotamia before 3000 B.C. However, recognition of these metals as chemical elements did not occur until modern times. Greek Concept of the Elements The Greek philosophers proposed that there are basic substances from which all things are made. Empedocles Empedocles , c.495–c.435 B.C., Greek philosopher, b. Acragas (present Agrigento), Sicily. Leader of the democratic faction in his native city, he was offered the crown, which he refused. A turn in political fortunes drove him and his followers into exile. ..... Click the link for more information. proposed four basic "roots," earth, air, fire, and water, and two forces, harmony and discord, joining and separating them. Plato Plato , 427?–347 B.C., Greek philosopher. Plato's teachings have been among the most influential in the history of Western civilization. Life After pursuing the liberal studies of his day, he became in 407 B.C. a pupil and friend of Socrates.

From about 388 B. ..... Click the link for more information. called the roots stoicheia (elements). He thought that they assume geometric forms and are made up of some more basic but undefined matter. A different theory, that of Leucippus Leucippus , 5th cent. B.C., Greek philosopher. Aristotle believed that Leucippus inspired the atomistic theory with which Democritus is identified. Little is known about Leucippus. ..... Click the link for more information. and his followers, held that all matter is made up of tiny indivisible particles (atomos). This theory was rejected by Aristotle Aristotle , 384–322 B.C., Greek philosopher, b. Stagira. He is sometimes called the Stagirite. Life Aristotle's father, Nicomachus, was a noted physician. Aristotle studied (367–347 B.C. ..... Click the link for more information. , who expanded on Plato's theory. Aristotle believed that different forms (eidos) were assumed by a basic material, which he called hulé.

The hulé had four basic properties, hotness, coldness, dryness, and moistness. The four elements differ in their embodiment of these properties; fire is hot and dry, earth cold and dry, water cold and moist, and air hot and moist. Although Aristotle proposed that an element is "one of those simple bodies into which other bodies can be decomposed and which itself is not capable of being divided into others," he thought the metals to be made of water, and called mercury "silver water" (chutos arguros). His idea that matter was a single basic substance that assumed different forms led to attempts by the alchemists to transmute other metals into gold. Evolution of Modern Concepts Although much early work was done in chemistry, especially with metals, and many recipes were recorded, there were few developments in the conception of the elements. In the 16th cent. Paracelsus Paracelsus, Philippus Aureolus , 1493?–1541, Swiss physician and alchemist. His original name Theophrastus Bombastus von Hohenheim.

He traveled widely, acquiring knowledge of alchemy, chemistry, and metallurgy, and although his egotism and his contempt for traditional ..... Click the link for more information. proposed salt, mercury, and sulfur as three "principles" of which bodies were made, although he apparently also believed in the four "elements." Van Helmont (c.1600) rejected the four elements and three principles, substituting two elements, air and water. Robert Boyle Boyle, Robert, 1627–91, Anglo-Irish physicist and chemist. The seventh son of the 1st earl of Cork, he was educated at Eton and on the Continent and conducted most of his researches at his own laboratories at Oxford (1654–68) and London (1668–91). ..... Click the link for more information. rejected these early theories and proposed a definition of chemical elements that led to the currently accepted definition. His definition is strikingly similar to Aristotle's earlier definition.

In The Sceptical Chymist (1661) Boyle wrote, "I now mean by elements … certain primitive and simple, or perfectly unmingled bodies; which not being made of any other bodies, or of one another, are the ingredients of which all those called perfectly mixed bodies [chemical compounds] are immediately compounded, and into which they are ultimately resolved." Whereas Aristotle and other early philosophers tried to determine the identity of the elements solely by reason, Boyle and later scientists used the results of numerous experiments to identify the elements. In 1789 Antoine Lavoisier Lavoisier, Antoine Laurent , 1743–94, French chemist and physicist, a founder of modern chemistry. He studied under eminent men of his day, won early recognition, and was admitted to the Academy of Sciences in 1768. ..... Click the link for more information. published a list of chemical elements based on Boyle's definition; this encouraged adoption of standard names for the elements. Although some of his elements are now known to be compounds, such as metallic oxides and salts, they were at the time accepted as elements since they could not be decomposed by any method then known.

In 1803 John Dalton Dalton, John , 1766–1844, English scientist. He revived the atomic theory (see atom), which he formulated in the first volume of his New System of Chemical Philosophy (2 vol., 1808–27). ..... Click the link for more information. proposed (as part of his atomic theory) that all atoms of an element have identical properties (including mass), that these atoms are unchanged by chemical action, and that atoms of different elements react with one another in simple proportions. Although symbols for some of the elements already existed, they were by no means universally accepted, and each compound also had a unique symbol that was unrelated to its chemical composition. Dalton devised a new set of circular symbols for the elements and used a combination of elemental symbols to represent a compound. For example, his symbol for oxygen was ◯, and for hydrogen ⊙. Since he thought water contained one atom of hydrogen for every atom of oxygen, he formed the symbol for water by writing the symbols for hydrogen and oxygen touching one another, ⊙◯. J. J.

Berzelius Berzelius, Jöns Jakob, Baron , 1779–1848, Swedish chemist, M.D. Univ. of Uppsala, 1802. He was noted for his work as teacher at the medical school and other institutions in Stockholm and for his discoveries in diverse fields of chemistry. ..... Click the link for more information. was the first to use the modern method, letting one or two letters of the element's name serve as its symbol. He also published an early table of atomic weights of 24 elements with most values very close to those now in use. Discovery of the Elements As noted above, some of the elements were discovered in prehistoric times but were not recognized as elements. Arsenic was discovered around 1250 by Albertus Magnus Albertus Magnus, Saint , or Saint Albert the Great, b. 1193 or 1206, d. 1280, scholastic philosopher, Doctor of the Church, called the Universal Doctor. A nobleman of Bollstädt in Swabia, he joined (1223) the Dominicans and taught at Hildesheim, Freiburg, .....

Click the link for more information. , and phosphorus was discovered about 1674 by Hennig Brand, an alchemist, who prepared it by distilling human urine. Only 12 elements were known before 1700, and only about twice that many by 1800, but by 1900 over 80 elements had been identified. In 1919 Ernest Rutherford Rutherford, Ernest Rutherford, 1st Baron, 1871–1937, British physicist, b. New Zealand. Rutherford left New Zealand in 1895, having earned three degrees from the Univ. ..... Click the link for more information. found that hydrogen was given off when nitrogen was bombarded with alpha particles. This first transmutation encouraged further study of nuclear reactions, and eventually led to the discovery in 1937 of technetium, the first synthetic element. Neptunium (atomic number 93) was the first transuranium element transuranium elements, in chemistry, radioactive elements with atomic numbers greater than that of uranium (at. no. 92).

All the transuranium elements of the actinide series were discovered as synthetic radioactive isotopes at the Univ. ..... Click the link for more information. to be synthesized (1940). Its discovery prompted the search that has led to the ongoing synthesis of additional transuranium elements. Bibliography See J. Emsley, The Elements (1991); A. Swertka, A Guide to the Elements (1996); P. W. Atkins, The Periodic Kingdom (1997); N. N. Greenwood and A. Earnshaw, Chemistry of the Elements (2d ed. 1997). element (el -ĕ-mĕnt) Any of a large number of substances, including hydrogen , helium , carbon, nitrogen, oxygen, and iron, that consist entirely of atoms of the same atomic number , i.e. with the same number of protons in their nuclei. The atoms are not all identical however: isotopes of an element can occur with different numbers of neutrons in their nuclei. When arranged in order of increasing atomic number along a series of horizontal rows, elements with similar chemical and physical properties fall into groups.

The similarities in properties arise from similarities in the electron arrangements within the atom. This table of elements is called the periodic table. Over 100 elements are now known, more than 90 of which occur naturally on Earth. The elements have stable isotopes and/or unstable (i.e. radioactive) isotopes. The creation of the elements and the means by which they become distributed throughout the Universe are major areas of study in astronomy (see nucleosynthesis ). The abundance of each element in the Universe, i.e. its cosmic abundance , depends on the method of its synthesis – by nuclear reactions in stars, by cosmic-ray collisions, etc. – and on its lifetime in its immediate surroundings and its long-term stability. Element An integral part of the sub- or superstructure having its own functional requirements; such as foundations, walls, floors, roofs, stairs and structural framework. Element (1) Among ancient Greek materialist philosophers, the basic constituents of nature; Empedocles believed the four basic elements to be fire, air, water, and earth. In ancient Chinese philosophy, the basic elements were thought to be metal, earth, water, wood, and fire.

(2) In the plural, a phenomenon or force of nature, such as a storm, that is regarded as irrepressible. (3) In a figurative sense, one’s habitual environment or surroundings; a favorite, familiar occupation or pursuit. element [′el·ə·mənt] (chemistry) A substance made up of atoms with the same atomic number; common examples are hydrogen, gold, and iron. Also known as chemical element. (computer science) One of the items of data in an array . element (language, text) One kind of node in an SGML , HTML , or XML document tree . An SGML element is typically represented by a start tag ("<p>") and an end tag ("</p>"). In some SGML implementations, some tags are omissible, as with "</p>" in HTML . The start tag can contain attributes ("<p lang="en-UK" class='stuff'>"), which are an unordered set of key-value bindings for that element. Both the start tag and end tag for an element typically contain the "tag name" (also called the " GI " or generic identifier) for that element.

In XML , an element is always represented either by an explicit start tag and end tag, or by an empty element tag ("<img src='thing. png ' alt='a dodad' />"). Other kinds of SGML node are: a section of character data ("foo"), a comment ("<!-- bar -->"), a markup declaration ("<!ENTITY reg CDATA '®'>"), or a processing instruction ("<?xml-stylesheet href="shop-english.xsl" type="text/xsl" ?>"). Element 89 | Article about Element 89 by The Free Dictionary Element 89 | Article about Element 89 by The Free Dictionary Also found in: Dictionary , Thesaurus , Medical , Wikipedia . actinium (ăktĭn`ēəm) [Gr.,=like a ray], radioactive chemical element; symbol Ac; at. no. 89; mass number of most stable isotope isotope , in chemistry and physics, one of two or more atoms having the same atomic number but differing in atomic weight and mass number. The concept of isotope was introduced by F. ..... Click the link for more information. 227; m.p. about 1,050&degC;; b.p.

3,200&degC;±300&degC;; sp. gr. 10.07; valence +3. Actinium is a silver-white metal with a cubic crystalline structure. It is found with uranium minerals in pitchblende pitchblende , dark, lustrous, heavy mineral, a source of radium and uranium. Largely natural uranium oxides, triuranium octaoxide (U3O8) and uranium dioxide (UO2 ..... Click the link for more information. . The pure metal can be prepared by reducing its fluoride with lithium vapor at about 1,200&degC;. Actinium-227, the most stable isotope, has a half-life half-life, measure of the average lifetime of a radioactive substance (see radioactivity) or an unstable subatomic particle. One half-life is the time required for one half of any given quantity of the substance to decay. ..... Click the link for more information. of 21.77 years. The other seven isotopes of actinium have very short half-lives ranging from 10 days to less than 1 min.

Actinium is in Group 3 of the periodic table periodic table, chart of the elements arranged according to the periodic law discovered by Dmitri I. Mendeleev and revised by Henry G. J. Moseley. In the periodic table the elements are arranged in columns and rows according to increasing atomic number (see the table entitled ..... Click the link for more information. . Its chemical properties are similar to those of lanthanum lanthanum [Gr.,=to lie hidden], metallic chemical element; symbol La; at. no. 57; at. wt. 138.90547; m.p. about 920&degC;; b.p. about 3,460&degC;; sp. gr. 6.19 at 25&degC;; valence +3. ..... Click the link for more information. and of members of the actinide series actinide series, a series of radioactive metallic elements in Group 3 of the periodic table. Members of the series are often called actinides, although actinium (at. no. 89) is not always considered a member of the series. ..... Click the link for more information.

, of which it is usually considered the first member. It reacts with water to form an insoluble hydroxide; with halides to form a trifluoride, trichloride, bromide, or iodide; with oxalic acid to form the oxalate; with oxygen or sulfur to form the sesquioxide or sesquisulfide. Actinium was first recognized in 1899 by André Debierne in uranium residues from pitchblende after the radium was extracted by Pierre and Marie Curie Curie , family of French scientists. Pierre Curie, 1859–1906, scientist, and his wife, Marie Sklodowska Curie, 1867–1934, chemist and physicist, b. Warsaw, are known for their work on radioactivity and on radium. ..... Click the link for more information. . It was later found to be identical with an element discovered in 1902 by Fritz Giesel and which he called emanium. Actinium Ac, a radioactive chemical element in the Group III of the Mendeleev periodic table, atomic number 89. No stable isotopes.

Actinium was discovered in 1899 by the French chemist A. Debierne while he was studying uranium ore tailings. The ten known radioactive isotopes of actinium have mass numbers ranging from 221 to 230. The longest-lived actinium isotope, 227Ac (half-life T½=21.8 years), emits beta particles (98.8 percent) and alpha particles (1.2 percent). The isotopes 227Ac and 228Ac (T½=6.13 h; also known as mesothorium II, MsThll) occur naturally in uraniferous and thoriferous ores as members of the naturally occurring radioactive families. The surface layer of the earth’s crust (thickness 1.6 km) contains 11,300 tons of 227Ac, but the actinium content in the earth’s crust is very small compared to that of other elements (6.10-10 percent by mass).

The element actinium is a silvery white metal with a face-centered cubic lattice (Tm=1050° ± 50°C, Tb probably about 3300°C); it glows faintly in the dark because of its high radioactivity. In moist air it becomes coated with a white film of oxide which prevents further oxidation of the metal. Actinium is trivalent in chemical compounds. Almost all actinium salts are white and are colorless in solution. Most of them (except AcP04) are isomorphic with the corresponding lanthanum compounds. Actinium forms the same insoluble compounds as does La (hydroxide, phosphate, oxalate, carbonate, fluosilicate). Actinium hydroxide Ac(OH)3 is more basic than lanthanum hydroxide La(OH)3. Because of the extraordinary similarities between the chemical properties of actinium and lanthanum, isolation of actinium in pure form from its natural hosts (containing La and other rare earths) involves great difficulties, and therefore milligram amounts of actinium (227Ac) are obtained artificially through neutron bombardment of radium 226Ra.

Since probability of 227Ac decay with alpha emission is low, and the energy of beta particles emitted by this isotope is very small (46 keV), any emission accompanying the radioactive decay of 227Ac went undetected for a long time; until 1935 it was assumed that radioactive decay of 227Ac occurred without emission. Modern instruments are capable of identifying such soft beta radiation, but it is still quite difficult to make quantitative measurements; therefore, the behavior of 227Ac is usually monitored in terms of the activity of its daughters, in experiments involving trace amounts of the radionuclide. Mixed with beryllium, 227Ac is used in the preparation of neutron sources, in which neutrons are formed by irradiating 9Be nuclei with alpha particles emitted by 227Ac daughters. REFERENCES Actinium - Element information, properties and uses | Periodic Table Chemistry in its element: actinium (Promo) You're listening to Chemistry in its element brought to you by Chemistry World, the magazine of the Royal Society of Chemistry. (End promo) This week, a glowing element that significantly changed the periodic table.

Richard Corfield When I was a little boy my father used to tell a story about a acquaintance of his who kept a lump of rock in his desk. His party trick - after a few drinks - was to draw the curtains, touch the pebble to the forehead of a volunteer, turn out the light and lead the hilarity as the victim's face blazed with a ghostly blue light. Eventually my father's acquaintance died and his executor started to dispose of his possessions. Finding the lump of rock in his desk, and noticing the sourceless dull blue glow that surrounded it he sought advice. Within hours the house had been sealed off and men in white environment suits with tongs and a lead box were relocating the magic pebble to the Atomic Energy Research Establishment at Harwell in Oxfordshire, the secret hub of Britain's nuclear research and development industry from the end of the Second World War to the 1990s. The pebble was, of course, pitchblende; the naturally occurring mineral that Pierre and Marie Curie had used as the source of the radioactive elements that they discovered in the closing years of the 19th century.

Pitchblende does not just contain actinium (the topic of this podcast), it also contains radium, radon and polonium; the latter, if we are to believe recent news reports, the Russian assassin's toxin of choice. Actinium, like radium and polonium, emits an ethereal blue radiance which contributes to pitchblende's luminescent properties. Although, radium, radon and polonium were observed first, of all the components of pitchblende actinium was the first to be isolated. Actinium was discovered by Andre-Louis Debierne, a friend of Marie and Pierre Curie who worked with them on isolating the radioactive elements in pitchblende. Although he published descriptions of the element in 1899 and then again in 1900 there is some doubt as to whether his techniques had actually allowed the element to be properly identified. What is clear however, is that the German chemist Friedrich Oskar Giesel was also investigating actinium and, by 1904, had unambiguously isolated it. Because of the glow that emanated from it he named his new element emanium.

Giesel was an admirer and loyal supporter of the Curie's and consequently was not interested in disputing the priority of discovery of a radioactive element that had come out of a lab whose work he admired hugely. Hence when it became clear that Debierne and Giesel were working on the same element Giesel was content to allow the Frenchman's claim to priority stand, and so today the element is still known by the name Debierne gave it - actinium. Whoever discovered it, actinium has an important place in the history of chemistry. It was the first of the non-primordial elements to be discovered. Primordial elements are those that have existed in their current state since before the Earth was formed. In other words their half-life is greater than about 108 years. All stable elements are primordial, as are many radioactive elements. Chemically, actinium, which in its native form is a silvery metal, has similar characteristics to that of the other rare earth elements such as lanthanum. Actinium has thirty-six isotopes all of which are radioactive. 227Ac, the isotope which comprises all naturally occurring actinium has the longest half-life at 21,773 years.

All the remaining radioactive isotopes have half-lives of the less than ten hours, the majority having half-lives of less than a minute. 227Ac is about a hundred and fifty times as radioactive as radium making a valuable as the neutron source of energy. Although actinium is found in trace of amounts in uranium ore, more commonly it is synthesised in milligram amounts by the neutron irradiation of radium-226 in a nuclear reactor. Actinium gives its name to a block of fifteen elements that lie between actinium and lawrencium in the periodic table with atomic numbers 89 through 103. These actinides - or actinoides as they are more correctly known these days - gain their name from the first element in the series, actinium, itself named after the Greek word for ray thus reflecting the element's - already mentioned - visible radioactivity. The actinoides were the first major addition to be made to Mendeleev's periodic table. American physicist Glenn T Seaborg was experiencing unexpected difficulty isolating the elements americium and curium during his work with the Manhattan Project during the second world war.

He found himself wondering if these elements more properly belonged to a different series from the transition metals, which would explain the differing chemical properties of the new elements he was synthesising in the nuclear reactor at Berkeley University in California. In 1945, Seaborg formally proposed the actinides and in so doing created the most significant change to the periodic table since Mendeleev's creation of it in 1869. Early in his career, Seaborg was a pioneer in the study of nuclear medicine and developed numerous isotopes of elements with important applications in the diagnosis and treatment of diseases, most notably 131Iodine which is used in the treatment of thyroid disease. Actinium also has a role to play in nuclear medicine. 225Ac can be used as the active agent in Targeted Alpha Therapy (TAT) a technique for inhibiting the growth of secondary cancers by direct irradiation with nuclear material, in this case 213Bi derived from 225Ac. And so an element discovered in the same mineral - pitchblende - which kick-started the whole science of nuclear chemistry, today stands at the crossroads of one of the most challenging of all medical disciplines - finding a cure for cancer.

The irony is that pitchblende inflicted a dreadful toll on those who worked with it in the early years of the study of radioactivity. Marie Curie suffered terrible radiation burns from handling it, and eventually, in later life, contracted radiation-induced aplastic anaemia from which she died. Even today Marie Curie's papers from the summit of her career in the 1890s - including her cookbook - are still considered too dangerous to handle, and are kept in lead-lined boxes Meera Senthilingam So whilst offering hope for treating the deadly effects of cancer, the element itself had deadly effects on its founders and therefore must be handled with care. That was science writer Richard Corfield with the radio active chemistry of actinium. Now next week we go beyond the actinides. Simon Cotton When the last member of the actinide series, element 103 or Lawrencium, was discovered, I was at school doing my A levels. The isotope found had a mass of 258 and it didn't hang about for long - it had a half-life of just 3.8 seconds. This was not unexpected as half lives had been getting shorter right along the actinide series.

This discovery prompted the scientific community to start asking, are there any elements waiting to be made beyond lawrencium, and if so, where would they fit in the periodic table? Meera Senthilingam Join Simon Cotton to find out how element 104, rutherfordium was discovered and how its place in the periodic table was found, in next week's Chemistry in its element. Until then, I'm Meera Senthilingam and thank you for listening. (Promo) Chemistry in its element is brought to you by the Royal Society of Chemistry and produced by thenakedscientists.com . There's more information and other episodes of Chemistry in its element on our website at chemistryworld.org/elements . (End promo) Pa Element or Protactinium Facts Pa Element or Protactinium Facts Pa Element or Protactinium Facts Chemical & Physical Properties of Pa Protactinium or Pa is a radioactive element with 91 protons. Todd Helmenstine Protactinium is a radioactive element predicted to exist in 1871 by Mendeleev , although it was not discovered until 1917 or isolated until 1934.

Here are useful and interesting Pa element facts: Name: Protactinium Symbol: Pa Atomic Weight: 231.03588 Discovery: Fajans & Gohring 1913; Fredrich Soddy, John Cranston, Otto Hahn, Lise Meitner 1917 (England/France). Protactinium was not isolated as a pure element until 1934 by Aristid von Grosse. Electron Configuration: [Rn] 7s2 5f2 6d1 Word Origin: Greek protos, meaning 'first'. Fajans and Gohring in 1913 named the element brevium , because the isotope they discovered, Pa-234, was short-lived. When Pa-231 was identified by Hahn and Meitner in 1918, the name protoactinium was adopted because this name was considered to be more consistent with the characteristics of the most abundant isotope (protactinium forms actinium when it radioactively decays). In 1949, the name protoactinium was shortened to protactinium.

continue reading below our video Test Your General Science Knowledge Isotopes: Protactinium has 13 isotopes . The most common isotope is Pa-231, which has a half-life of 32,500 years. The first isotope to be discovered was Pa-234, which was also called UX2. Pa-234 is a short-lived member of the naturally occurring U-238 decay series. The longer-lived isotope, Pa-231, was identified by Hahn and Meitner in 1918. Properties: The atomic weight of protactinium is 231.0359, its melting point is < 1600°C, specific gravity has been calculated to be 15.37, with a valence of 4 or 5. Protactinium has a bright metallic luster which is retained for a while in air. The element is superconductive below 1.4K. Several protactinium compounds are known, some of which are colored. Protactinium is an alpha emitter (5.0 MeV) and is a radiological hazard which requires special handling.

Protactinium is one of the rarest and most expensive naturally occurring elements. Sources: The element occurs in pitchblende to the extent of about 1 part Pa-231 to 10 million parts ore. In general, Pa only occurs at a concentration of a few parts per trillion in the Earth's crust. Other Interesting Protactinium Facts In solution, the +5 oxidation state quickly combines with hydroxide ions to form (radioactive) hydroxy-oxide solids that stick to the surface of the container. Protactinium has no stable isotopes. Handling of protactinium is similar to that of plutonium, due to its potent radioactivity. Even if it was not radioactive, protactinium would present a health risk because the element is also a toxic metal. The largest amount of protactinium obtained to date was 125 grams, which the Great Britain Atomic Energy Authority extracted from 60 tons of nuclear waste. Although protactinium has few uses aside from research purposes, it may be combined with the isotope thorium-230 to date marine sediments. The estimated cost of one gram of protactinium is about $280.

Element Classification: Radioactive Rare Earth ( Actinide ) Density (g/cc): 15.37 transition element | chemical element | Britannica.com Transition element Alternative Titles: d-block element, transition metal Related Topics zirconium (Zr) Transition element, any of various chemical elements that have valence electrons—i.e., electrons that can participate in the formation of chemical bonds—in two shells instead of only one. While the term transition has no particular chemical significance, it is a convenient name by which to distinguish the similarity of the atomic structures and resulting properties of the elements so designated. They occupy the middle portions of the long periods of the periodic table of elements (see Figure ) between the groups on the left-hand side and the groups on the right. Specifically, they form Groups 3 (IIIb) through 12 (IIb). General properties of the group The most striking similarities shared by the 24 elements in question are that they are all metals and that most of them are hard, strong, and lustrous, have high melting and boiling points, and are good conductors of heat and electricity. The range in these properties is considerable; therefore the statements are comparative with the general properties of all the other elements.

Many of the elements are technologically important: titanium , iron , nickel , and copper , for example, are used structurally and in electrical technology. Second, the transition elements form many useful alloys , with one another and with other metallic elements. Third, most of these elements dissolve in mineral acids, although a few, such as platinum , silver , and gold , are called “noble”—that is, are unaffected by simple (nonoxidizing) acids. Without exception, the elements of the main transition series (i.e., excluding the lanthanoids and actinoids as specified below) form stable compounds in two or more formal oxidation states. The transition elements may be subdivided according to the electronic structures of their atoms into three main transition series, called the first, second, and third transition series, and two inner transition series, called the lanthanoids and the actinoids. Similar Topics calcium (Ca) The first main transition series begins with either scandium (symbol Sc, atomic number 21) or titanium (symbol Ti, atomic number 22) and ends with zinc (symbol Zn, atomic number 30).

The second series includes the elements yttrium (symbol Y, atomic number 39) to cadmium (symbol Cd, atomic number 48). The third series extends from lanthanum (symbol La, atomic number 57) to mercury (symbol Hg, atomic number 80). These three main transition series are included in the set of 30 elements often called the d-block transition elements. Because scandium, yttrium, and lanthanum actually do not form compounds analogous to those of the other transition elements and because their chemistry is quite homologous to that of the lanthanoids, they are excluded from the present discussion of the main transition elements. Similarly, because zinc, cadmium, and mercury exhibit few of the properties characteristic of the other transition elements, they are treated separately (see zinc group element ). The remaining d-block transition elements and some of their characteristic properties are listed in the Table. Some properties of the transition elements symbol 1,064 2,856 The first of the inner transition series includes the elements from cerium (symbol Ce, atomic number 58) to lutetium (symbol Lu, atomic number 71).

These elements are called the lanthanoids (or lanthanides) because the chemistry of each closely resembles that of lanthanum. Lanthanum itself is often regarded as one of the lanthanoids. The actinoid series consists of 15 elements from actinium (symbol Ac, atomic number 89) to lawrencium (symbol Lr, atomic number 103). These inner transition series are covered under rare-earth element and actinoid element . For elements 104 and higher, see transuranium element . The relative locations of the transition elements in the periodic table and their chemical and physical properties can best be understood by considering their electronic structures and the way in which those structures vary as atomic numbers increase. Atomic orbitals of the hydrogen atom Open Door policy Throughout the next period the pattern of variation of the orbital energies is similar to that immediately preceding. When the configuration of the noble gas, krypton, has been achieved, the 5s orbital is more stable than the 4d orbitals.

The next two electrons therefore enter the 5s orbital, but then the 4d orbitals fall to lower energy than the 5p orbitals, and the second regular transition series commences with the element yttrium. Electrons continue to be added to the 4d orbitals until those orbitals are entirely filled at the position of the element cadmium, which has an electron configuration [Kr] 4d105s2. The next six electrons enter the 5p orbitals until another noble gas configuration is attained at the element xenon . Analogously to the two preceding periods, the next two electrons are added to the next available orbital, namely, the 6s orbital, producing the next two elements, cesium and barium . At this point, however, the ordering of orbitals becomes more complex than it previously had been, because there are now unfilled 4f orbitals as well as the 5d orbitals, and the two sets have approximately the same energy.

In the next element, lanthanum (atomic number 57), an electron is added to the 5d orbitals, but the immediately following element, cerium (atomic number 58), has two electrons in the 4f orbitals and none in the 5d orbitals. Through the next 12 elements the additional electrons enter the 4f orbitals, although the 5d orbitals are of only slightly higher energy. This set of elements, spanning the range from lanthanum, where the 4f orbitals were still vacant or about to be filled, through lutetium, in which the 4f orbitals are completely filled by 14 electrons, makes up the lanthanoids, mentioned above. At this point the next available orbitals are the 5d orbitals, and the elements hafnium through gold, the third regular transition series, correspond to the successive filling of these 5d orbitals. Following this series there are again p orbitals (6p) to be filled, and when this is accomplished the noble gas radon is reached.

Molecular orbitals If two atoms are close together, some of their orbitals may overlap and participate in the formation of molecular orbitals. Electrons that occupy a molecular orbital interact with the nuclei of both atoms: if this interaction results in a total energy less than that of the separated atoms, as is the case if the orbital lies mainly in the region between the two nuclei, the orbital is said to be a bonding orbital and its occupancy by electrons constitutes a covalent bond that links the atoms together in compound formation and in which the electrons are said to be shared. If the occupation of an orbital by electrons raises the energy of the system, as is the case if the orbital lies mainly outside the region between the two nuclei, that orbital is said to be antibonding; the presence of electrons in such orbitals tends to offset the attractive force derived from the bonding electrons. A bonding or an antibonding molecular orbital may be disposed along the line passing through the two nuclei, in which case it is designated by the Greek letter σ (sigma); or it may occupy regions approximately parallel to that line and be designated π (pi).

Discovery of the transition elements The most abundant transition element in the Earth’s solid crust is iron, which is fourth among all elements and second (to aluminum) among metals in crustal abundance. The elements titanium, manganese , zirconium , vanadium , and chromium also have abundances in excess of 100 grams (3.5 ounces) per ton. Some of the most important and useful transition elements have very low crustal abundances—e.g., tungsten , platinum, gold, and silver. Four of the regular transition elements were known to the ancients: iron (ferrum), copper (cuprum), silver (argentum), and gold (aurum). Their chemical symbols (Fe, Cu, Ag, Au), in fact, are derived from their alchemical (Latin) names rather than their contemporary names. The other regular transition elements were discovered (or recognized as elements) after the early 18th century. The transition element most recently discovered in nature is rhenium (atomic number 75), which in 1925 was detected in platinum ores and in the niobium mineral columbite.

Technetium (atomic number 43) is the only d-block element that has not been isolated from the Earth’s crust. All isotopes of technetium are radioactive; the half-life of even the stablest isotope , technetium-97, is too short to permit the survival of primordial technetium in the Earth’s crust, and claims that it has been isolated or detected there must be considered erroneous . Technetium can be isolated in considerable quantities, however, from the fission products of nuclear reactors, and it is at least as readily available for chemical study as the naturally occurring similar element rhenium, of which there are no concentrated ores. Transition-metal catalysts One important use of transition metals and their compounds is as catalysts for a variety of industrial processes, mostly in the petroleum and polymer (plastics, fibres) industries, in which organic molecules are isomerized, built up from simple molecules, oxidized, hydrogenated, or caused to polymerize . Only a few of the most important such processes and their catalysts can be mentioned here.

Catalysts are of two physical types: homogeneous (i.e., dissolved in the reaction mixture) and heterogeneous (i.e., constituting a solid phase separate from and insoluble in the reaction mixture). Both types are represented on the industrial scene, but the latter are much more common. The introduction of catalysts that allow polymerization to be carried out at relatively low temperatures and pressures revolutionized the production of polyethylene and polypropylene. Previously polyethylene had to be made by a process requiring pressures of about 1,000 atmospheres, and polypropylene of useful properties was not commercially important. The catalysts devised and applied during the early 1950s are prepared from titanium tetrachloride and an aluminum alkyl such as triethylaluminum: the precipitated, titanium-containing solid, plus the excess aluminum alkyl in solution, constitutes the catalyst . A very different sort of catalyst, consisting of chromium trioxide dispersed on silica-alumina, performs similarly in polymerizing ethylene but cannot produce a useful form of polypropylene.

Chromium in the form of chromium sesquioxide, or chromic oxide, on alumina is the major industrial catalyst for transforming saturated hydrocarbons (i.e., those in which all available valence bonds of the atoms are attached to other atoms) to useful olefins (unsaturated organic compounds), chiefly n-butane to butylene and butadiene. Iron-containing catalysts are used in various processes of which the most notable is that for producing ammonia from nitrogen and hydrogen. This process, developed early in the 20th century, represents the first major industrial application of transition metal catalysis. The catalyst is magnetic triiron tetroxide (Fe3 O 4), “promoted” by the addition of small quantities of potassium oxide, aluminum oxide, calcium oxide, and silica. Molybdenum in molybdenum trioxide–aluminum oxide mixtures or in cobalt oxide–molybdenum trioxide–aluminum oxide mixtures finds many applications, such as desulfurizing gases and liquids; removing lead , nickel, and vanadium from petroleum refinery feed stocks; and in modifying, or “reforming,” crude petroleum fractions to increase their octane rating.

Olefins that are free of such impurities as carbon monoxide, sulfur , halogen, and compounds of arsenic or lead (catalyst poisons), can be hydrogenated (i.e., combined with hydrogen) at atmospheric pressure and room temperature, using various types of active nickel preparations as catalysts. Copper is a component of a variety of catalysts, of which the copper chromites, used for selective hydrogenation of carbonyl groups (compounds containing the organic radical C = O), are perhaps the most important. Fats and oils can also be hydrogenated to alcohols using copper catalysts. Palladium chloride together with salts of copper in the +1 oxidation state forms a homogeneous catalyst for oxidizing ethylene to acetaldehyde (Wacker process), but commercial use of this process has been abandoned. Metallic platinum has a broad spectrum of catalytic activities. One of the most important in terms of tonnage production is in catalytic reforming of petroleum fractions to improve antiknock quality of gasoline. Silver oxide, on an inactive, refractory support, catalyzes oxidation of ethylene to ethylene oxide.

The oxo process (also called hydroformylation), in which certain olefins react with carbon monoxide and hydrogen to give aldehydes (a class of organic compounds that contain the group −CHO), requires a homogeneous catalyst containing a transition metal. The first practicable one was hydrogen tetracarbonylcobaltate, HCo(CO)4, which is formed in the reaction mixture by action of hydrogen on octacarbonyldicobalt, Co2(CO)8. More recently rhodium complexes have been found to have greater activity at lower temperatures and pressures and to be more easily recovered. The net reaction in the oxo process is represented by Page 1 of 2

Question: Which radioactive element, atomic number 89, is the first alphabetically in a list of naturally occurring elements?
Answer: ACTINIUM