KRYPTON

(Kr), chemical element, rare gas of Group 0 (noble gases) of the periodic table, forming very few chemical compounds. About three times heavier than air, krypton gas is colourless, odourless, and tasteless. Although traces are present in meteorites and minerals, krypton is more plentiful in the Earth's atmosphere, which contains 1 part krypton in about 900,000. The element was discovered (1898) by the British chemists Sir William Ramsay and Morris W. Travers in the residue left after a sample of liquid air had boiled almost entirely away. Krypton is produced on a small commercial scale by fractional distillation of liquid air. Krypton is used in certain fluorescent lamps and in a flash lamp employed in high-speed photography. Radioactive krypton-85 is useful for detecting leaks in sealed containers, with the escaping atoms detected by means of their radiation. Krypton gas liquefies at -152.30 C (-242 F) and freezes 4 C lower. When a current of electricity is passed through a glass tube containing krypton at low pressure, a bluish white light is emitted. The wavelength of an orange-red component of light emitted by stable krypton-86, because of its extreme sharpness, served as the international standard for the metre from 1960 to 1983. (One metre equals 1,650,763.73 times the wavelength of this line.) Krypton was considered for many years to be totally unreactive. In the early 1960s, however, krypton was found to react with the element fluorine when both are combined in an electrical-discharge tube; the compound formed is krypton difluoride, KrF2. Few other krypton compounds have been reported. Clathrate compounds, in which the element is trapped in cagelike structures of water or other molecules, are known. Molecules of krypton consist of single atoms. Natural krypton is a mixture of six stable isotopes: krypton-84 (57 percent); krypton-86 (17.3 percent); krypton-82 (11.6 percent); krypton-83 (11.5 percent); krypton-80 (2.25 percent); and krypton-78 (0.35 percent). About 20 radioactive isotopes, produced by fission of uranium and by other nuclear reactions, also are known. Krypton-85 has a half-life of 10.73 years. atomic number 36 atomic weight 83.80 melting point -156.6 C (-249.9 F) boiling point -152.3 C (-242.1 F) density (1 atm, 0 C) 3.733 g/litre valence 0,2 electronic config. 2-8-18-8 or (Ar)3d104s24p6