krypton(redirected from Element 36)
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Kr, a chemical element in Group VIII of the Mendeleev periodic system; one of the inert gases. Atomic number, 36; atomic mass, 83.80. On earth it is present mainly in the atmosphere. Atmospheric krypton is a mixture of six stable isotopes, among which 84Kr (56.90 percent) predominates. It was discovered in 1898 by W. Ramsay and M. Travers during spectroscopic studies of low-volatility liquid air fractions and was named krypton (from the Greek kryptos, “concealed”)- Under normal conditions 1m3 of air contains/about 1 cm3 of krypton.
Krypton is a colorless, odorless monatomic gas; its density at O°C and 100 kilonewtons per sq m (kN/m2), or 760 mm Hg, is 3.745 g/liter. Melting point, –157.1°C; boiling point, –153.2°C. Solid krypton has a cubic lattice, with lattice constant a = 5.706 angstroms (Å) at –184°C. After synthesis of xenon fluoride (1961), krypton was also shown to be capable of entering into chemical reactions. In particular, the reaction of krypton with fluorine (for example, in electric discharges) yields the fluorides Krp2 or Krp4, which are stable only at low temperatures. Barium kryptonate, BaKrO4, was prepared by the reaction of a solution of Ba(OH)2 with Krp4. Like the other inert gases, krypton forms the clathrate compounds Kr·6H2O, Kr·3C6H5OH, and others.
Krypton is produced by fractionation of air. It is used mainly in electrovaccum technology. Krypton incandescent lamps last longer than ordinary lamps (filled with nitrogen or argon), since the heavy atoms of krypton retard to a greater extent the evaporation of tungsten atoms from the surface of the incandescent filament. Electric discharge in tubes filled with krypton at low pressure is accompanied by a white glow.
S. S. BERDONOSOV
["An Essential Hybrid Reasoning System: Knowledge and Symbol Level Accounts of KRYPTON", R.J. Brachman et al, Proc IJCAI-85, 1985].