Krypton is the chemical element with atomic number 36 and atomic symbol Kr.  It is a member of the noble gasesAny of the halogen elements: helium neon, argon, xenon, radon, krypton (group 8 of the Periodic Table).  Krypton is found as a trace element in the Earth's atmosphere, and is colorless, odorless and tasteless. Krypton can be chemically isolated by fractionally distilling liquified air, and is frequently utilized with other rare gases in fluorescent lamps. Krypton is essentially inert with respect to chemical reaction with other elements and compounds across a broad variety of physical circumstances.

Krypton occurs naturally in the atmosphere at concentrations of approximately 1.14 parts per million by volume. Work by Cardelli et al. suggest that large quantities of krypton are present in interstellar space. There are six known stable isotopes of krypton and over thirty unstable isotopes.

Properties

At conditions near standard temperature and pressure, krypton (along with all noble gases) is a monatomic species, and is in a highly inert state. However, under certain condtions, krypton can enter into a reaction with halides to form krypton halides; moreover, such molecules are typically unstable and readily decompose. 

Krypton in solid form manifests a white color and forms in face-centered cubic crystal. Such a crystal structure is a shared property of the noble gases in solid form, other than for helium, which exhibits a close-packed hexagonal structure.

Discovery

Sir William Ramsay, a Scottish chemist, and Morris Travers, an English chemist discovered krypton in Great Britain in 1898 as part of a residue left from evaporating practically all the constituents of liquid air. The element neon was actually discovered by a similar procedure by the identical research team only several weeks subsequent to the krypton discovery. Ramsay was given the 1904 Nobel Prize in Chemistry for the discovery of a series of noble gases, including krypton.

Uses

An international agreement in the year 1960 defined the meter in terms of wavelength of light emitted by the krypton-86 isotope, having a wavelength of 605.78 nanometers. The gas can be used in lighting and photography. Krypton light has a significant number of spectral lines, and their high light intensity output within plasma permits krypton to be extremely useful in a number of  high-powered gas lasers, such as krypton ion and excimer lasers; each of these laser types select one of the spectral lines for  amplification. In addition, a specific krypton fluoride laser has a number of uses.

Due to its long half life of about 230,000 years ⁸¹Kr is sometmes utilized for the dating of ancient aquifers.

Human health effects

When present in high concentrations in the air that is breathed by people, krypton induces narcotic or sleep-inducing effects. Thus it is considered a psychoactive substance.

References

• John H. Holloway & Eric G. Hope (1998). A. G. Sykes. ed. Advances in Inorganic Chemistry. Academic Press.  ISBN 0-12-023646-X.
• Cardelli, Jason A.; Meyer, David M. (1996). "The Abundance of Interstellar Krypton". The Astrophysical Journal Letters. The American Astronomical Society. pp. L57–L60.
• Lide, D. R., ed. (2005). CRC Handbook of Chemistry and Physics (86th ed.). Boca Raton (FL): CRC Press. ISBN 0-8493-0486-5.
• Grosse, A. V.; Kirshenbaum, A. D.; Streng, A. G.; Streng, L. V. (1963). "Krypton Tetrafluoride: Preparation and Some Properties". Science 139 (3559): 1047–1048.