XENON

(Xe), chemical element, heavy and extremely rare gas of Group 0 (noble gases) of the periodic table. It was the first noble gas found to form true chemical compounds. More than 41/2 times heavier than air, xenon is colourless, odourless, and tasteless. Solid xenon belongs to the face-centred cubic crystal system, which implies that its molecules, which consist of single atoms, behave as spheres packed together as closely as possible. Xenon occurs in slight traces in gases within the Earth and is present to an extent of about 0.0000086 percent, or about one part in 10,000,000, by volume of dry air. Xenon is manufactured on a small scale by the fractional distillation of liquid air. The British chemists Sir William Ramsay and Morris W. Travers isolated the element (1898) by repeated fractional distillation of the noble gas krypton, which they had discovered six weeks previously. The element xenon is used in lamps that produce intense, extremely short flashes of light, such as stroboscopes and lights for high-speed photography. When a charge of electricity is passed through the gas at low pressure, it emits a flash of bluish-white light; at higher pressures white light resembling daylight is emitted. Xenon flash lamps are used to activate ruby lasers. Natural xenon is a mixture of nine stable isotopes in the following percentages: xenon-124 (0.096); xenon-126 (0.090); xenon-128 (1.92); xenon-129 (26.44); xenon-130 (4.08); xenon-131 (21.18); xenon-132 (26.89); xenon-134 (10.44); and xenon-136 (8.87). The xenon found in some stony meteorites shows a large proportion of xenon-129, believed to be a product of radioactive decay of iodine-129, whose half-life is 17,000,000 years. Study of the xenon-129 content of meteorites casts light on the history of the solar system. More than a dozen radioactive xenon isotopes produced by fission of uranium and other nuclear reactions are known. For example, xenon-135 (9.2-hour half-life) is produced by uranium fission in nuclear reactors, where it is troublesome because it absorbs fission-producing neutrons. Noble gases were thought to be chemically inert until Neil Bartlett produced (1962) the first noble-gas compound, a red crystalline solid, xenon hexafluoroplatinate(V), that can best be formulated as Xe(PtF6)x, in which x varies in value from one to two. Xenon was later observed to combine directly with fluorine to form a series of fluorides, XeF2, XeF4, and XeF6, of which the tetrafluoride (XeF4) is the easiest to prepare. The oxides XeO3 and XeO4, made indirectly in aqueous solution, are explosively unstable when dry. Stable, insoluble xenate(VIII) salts, such as that of sodium, Na4XeO68H2O, and several other stable compoundsfor example, the yellow solid cesium octafluoroxenate(VI), Cs2XeF8have been prepared and studied. atomic number 54 atomic weight 131.30 melting point -111.9 C (-169.6 F) boiling point -107.1 C (-160.6 F) density (1 atm, 0 C) 5.887 g/litre valence 0,2,4,6,8 electronic config. 2-8-18-18-8 or (Kr)4d105s25p6