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krypton(krĭp`tŏn) [Gr.,=hidden], gaseous chemical element; symbol Kr; at. no. 36; at. wt. 83.798; m.p. −156.6°C;; b.p. −152.3°C;; density 3.73 grams per liter at STPSTP
or standard temperature and pressure,
standard conditions for measurement of the properties of matter. The standard temperature is the freezing point of pure water, 0°C; or 273.15°K;.
..... Click the link for more information. ; valence usually 0. Krypton is a colorless, odorless, tasteless gas. It is one of the so-called inert gasesinert 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.
..... Click the link for more information. 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
..... Click the link for more information. . It is a rare gas present in air at a concentration of about one part per million. Naturally occurring krypton is a mixture of six stable isotopes. It is produced commercially by fractional distillation of liquid air. Krypton is used to fill electric lamp bulbs and various electronic devices. Fluorescent lamps are filled with a mixture of krypton and argon. Krypton is also used in tungsten-filament photographic projection lamps and in very high-powered electric arc lights used at airports. A mixture of stable and unstable isotopes of krypton is produced by slow neutron fission of uranium in nuclear reactors. Krypton-85 (half-life about 10 years) is the most stable of the 17 radioactive isotopes known; it makes up about 5% by volume of the krypton produced in the nuclear reactor. It is used to detect leaks in sealed containers, to excite phosphors in light sources with no external source of energy, and in medicine to detect abnormal heart openings. Although krypton does not generally form chemical compounds in the normal sense, gram quantities of krypton difluoride have been prepared and several other compounds have been reported. Krypton has characteristic green and orange lines in its spectrum. In 1960 the meter was defined by international agreement as exactly 1,650,763.73 times the wavelength (in a vacuum) of the orange-red line in the emission spectrum of krypton-86 (see weights and measuresweights and measures,
units and standards for expressing the amount of some quantity, such as length, capacity, or weight; the science of measurement standards and methods is known as metrology.
Crude systems of weights and measures probably date from prehistoric times.
..... Click the link for more information. ). Krypton was discovered in 1898 by William RamsayRamsay, Sir William,
1852–1916, Scottish chemist. He was professor of chemistry at University College, Bristol (1880–87), and at University College, London (1887–1912).
..... Click the link for more information. and W. M. Travers in residue from the evaporation of a sample of liquid air from which oxygen and nitrogen had been removed.
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].