xenon

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xenon

(zē`nŏn) [Gr.,=strange], gaseous chemical element; symbol Xe; at. no. 54; at. wt. 131.293; m.p. −111.9°C;; b.p. −107.1°C;; density 5.86 grams per liter at STP; valence usually 0. Xenon is a rare, colorless, odorless, tasteless, chemically unreactive gas. It is one of the inert gasinert gas
or noble gas,
any of the elements in Group 18 of the periodic table. In order of increasing atomic number they are: helium, neon, argon, krypton, xenon, and radon. They are colorless, odorless, tasteless gases and were once believed to be entirely inert, i.e.
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 elements found in Group 18 of the periodic tableperiodic 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
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. Xenon was long considered incapable of chemical reaction, but in 1962 Neil Bartlett, a Canadian chemist, reported synthesis of xenon hexafluoroplatinate, XePtF6, a true compound. Since that time a number of other xenon compounds have been reported. Xenon is present in the atmosphere in extremely low concentration (about one part in 20 million). It is obtained commercially from liquid air. Xenon is used in certain photographic flash lamps, in high-intensity arc lamps for motion picture projection, and in high-pressure arc lamps to produce ultraviolet light. It is used in numerous instruments for radiation detection, e.g., neutron and X-ray counters and bubble chambers. It has found some use in medicine, e.g., as an anesthetic (mainly in Russia). A mixture of oxygen with very high levels of xenon has been breathed by athletes prior to competition to boost erythropoietin (EPO) levels and increase red blood cells and thus enhance performance; such use was banned by the World Anti-Doping Agency in 2014. Naturally occurring xenon is a mixture of 9 stable isotopes; 20 short-lived radioactive isotopes are also known. A mixture of stable and unstable isotopes of xenon is produced in nuclear reactors during neutron fission of uranium; one of these, xenon-135, is a very good neutron absorber and must be removed since it poisons the reaction. Xenon was discovered spectroscopically in 1898 by William Ramsay and M. W. Travers, who obtained it by fractional distillation of an impure sample of krypton.

Xenon

 

Xe, a chemical element of group VIII of the periodic system of D. I. Mendeleev; an inert gas. Atomic number, 54; atomic weight, 131.30. On earth, xenon primarily occurs in the atmosphere. Atmospheric xenon is composed of nine stable isotopes, of which 129 Xe, 131 Xe, and 132 Xe predominate. Xenon was discovered in 1898 by the British scientists W. Ramsay and M. Travers, who subjected liquid air to gradual evaporation and then employed spectroscopic analysis to study its most poorly volatile fractions. It was found to be an impurity in krypton; hence its name (Greek xenos, “stranger”). Xenon is an extremely rare element. Under normal conditions 1,000 m3 of air contains approximately 87 cm3 of xenon.

Xenon is a colorless and odorless monatomic gas with a density of 5.851 g/l at 0°C and 105 newtons (N) per m2 (760 mm Hg). It has a melting point of — 111.8°C and a boiling point of —108.1°C. In the solid state xenon is characterized by a cubic lattice with unit-cell parameter of α = 6.25 Å (at — 185°C). The fifth (outer) electron shell in a xenon atom contains eight electrons and is highly stable. However, the attraction of outer electrons toward the atomic nucleus is screened by a large number of intermediate electron shells. Although the first ionization potential for xenon is rather high (12.13 eV), it is considerably lower than that of other stable inert gases. Therefore xenon was the first inert gas for which a chemical compound was successfully obtained; the Canadian chemist N. Bartlett isolated the compound XePtF6 in 1961.

Further investigations revealed that xenon can exhibit valences of I, II, IV, VI, and VIII. The compounds of xenon and fluorine (XeF2, XeF4, XeF6, XeF8) have been studied the most extensively; they are obtained under specific conditions with the aid of a nickel device. For example, XeF4 can be synthesized by the direct passage of a Xe—F2 mixture through a heated nickel tube. The synthesis of XeF2 can be achieved by ultraviolet irradiation of the Xe—Fe2 mixture. The successful preparation of the fluorides XeF6 and XeF8 is only possible at high pressures (up to 20 MN/m2, or 200 atm) and temperatures (300°-600°C). The most stable fluoride is XeF4 (it can be stored for prolonged periods at room temperature), while XeF8 exhibits the least stability (it is stored at temperatures below 77°K). Careful concentration by evaporation of a XeF4 solution in water produces an extremely unstable nonvolatile oxide, XeO3 (a powerful explosive). Barium xenonate, Ba3XeO6, can be prepared by treating XeF6 with a Ba(OH)2 solution. Salts containing octavalent xenon known as perxenates (for example, Na4XeO6 • 6H2O) also exist. The perxenate Na4XeO6•6H2O yields a higher oxide, XeO4, upon the action of sulfuric acid. Double salts, such as XeF2 • 2SbF5 and XeF6 • ASF3, as well as the perchlorate XeClO4 (a very strong oxidizing agent), are known to exist.

Industrial xenon is obtained from the air. Because of the very low xenon content in the atmosphere, the volume of xenon produced is small. Xenon is primarily used in high-power gas-discharge tubes. It is used in research and medicine. Thus, owing to its ability to absorb X-ray radiation, it is used in encephalography. Xenon fluorides are widely used as strong oxidizing and fluorinating agents. In the form of fluorides, it is advisable to store and transport extremely aggressive fluorine.

S. S. BERDONOSOV

xenon

[′zē‚nän]
(chemistry)
An element, symbol Xe, member of the noble gas family, group 0, atomic number 54, atomic weight 131.291; colorless, boiling point -108°C (1 atmosphere, or 101,325 pascals), noncombustible, nontoxic, and nonreactive; used in photographic flash lamps, luminescent tubes, and lasers, and as an anesthetic.

xenon

a colourless odourless gaseous element occurring in trace amounts in air; formerly considered inert it is now known to form compounds and is used in radio valves, stroboscopic and bactericidal lamps, and bubble chambers. Symbol: Xe; atomic no.: 54; atomic wt.: 131.29; valency: 0; density: 5.887 kg/m3; melting pt.: --111.76?C; boiling pt.: --108.0?C