Krypton

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Krypton

Krypton is a chemical element with the symbol Kr and atomic number 36. A colorless noble gas, krypton occurs in trace amounts in the atmosphere, is isolated by fractionating liquefied air, and is often used with other rare gases in fluorescent lamps. Krypton is inert for most practical purposes but it is known to form compounds with fluorine. Krypton can also form clathrates with water when atoms of it are trapped in a lattice of the water molecules.

Notable characteristics

Krypton, a so-called noble gas due to its very low chemical reactivity, is characterized by a brilliant green and orange spectral signature. It is one of the products of uranium fission. Solidified krypton is white and crystalline with a face-centered cubic crystal structure which is a common property of all "rare gases".

History

Krypton (Greek κρυπτός meaning "hidden") was discovered in Great Britain, 1898 by William Ramsay and Morris Travers in residue left from evaporating nearly all components of liquid air. In 1960 an international agreement defined the metre in terms of light emitted from a krypton isotope. This agreement replaced the longstanding standard metre located in Paris which was a metal bar made of a platinum-iridium alloy (the bar was originally estimated to be one ten millionth of a quadrant of the earth's polar circumference). In October 1983 the krypton standard was in turn replaced by the Bureau International des Poids et Mesures (International Bureau of Weights and Measures). A metre is now defined as the distance that light travels in a vacuum during 1/299,792,458 s. The fictional planet Krypton, home of the popular comic book and movie hero Superman, was named after this element, as is Superman's weakness, Kryptonite.

Occurrence

The concentration of krypton in earth's atmosphere is about 1 ppm. It can be extracted from liquid air by fractional distillation.^*

Compounds

Like the other noble gases, krypton is widely considered to be chemically inert. Studies conducted since the 1960s have uncovered some compounds of krypton. Krypton difluoride has been made in gram quantities and can be produced in several different ways. Other fluorides and a salt of a krypton oxoacid have also been found. ArKr+ and KrH+ molecule-ions have been investigated and there is evidence for KrXe or KrXe+.

At the University of Helsinki in Finland, HKrCN and HKrCCH (krypton hydride-cyanide and hydrokryptoacetylene) were synthesized and determined to be stable up to 40K(M. Räsänen et al.). See http://pubs.acs.org/cen/80th/noblegases.html in its paragraph starting "Many recent findings".

Isotopes

Naturally occurring krypton is made of five stable and one slightly radioactive isotope. Krypton's spectral signature is easily produced with some very sharp lines. Kr-81 is the product of atmospheric reactions with the other naturally occurring isotopes of krypton. It is radioactive with a half-life of 250,000 years. Like xenon, krypton is highly volatile when it is near surface waters and Kr-81 has therefore been used for dating old (50,000 - 800,000 year) groundwater. Kr-85 is an inert radioactive noble gas with a half-life of 10.76 years, that is produced by fission of uranium and plutonium. Sources have included nuclear bomb testing, nuclear reactors, and the release of Kr-85 during the reprocessing of fuel rods from nuclear reactors. A strong gradient exists between the northern and southern hemispheres where concentrations at the North Pole are approximately 30% higher than the South Pole due to the fact that most Kr-85 is produced in the northern hemisphere, and north-south atmospheric mixing is relatively slow.

Krypton fluoride laser

One major use of krypton is the krypton fluoride laser. Certain amounts of energy are added to force krypton gas to react with fluorine gas to become KrF excited state complex.

The compound will decompose once the energy supply stops. During the decomposition process, the excess energy stored in the excited state complex will be emitted in the form of strong ultraviolet laser radiation.

External links

References

Los Alamos National Laboratory - Krypton
USGS Periodic Table - Krypton
"Chemical Elements: From Carbon to Krypton" By: David Newton & Lawrence W. Baker
"Krypton 85: a Review of the Literature and an Analysis of Radiation Hazards" By: William P. Kirk

Chemical elements | Noble gases

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