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Atomic Symbol: Kr
Atomic Number: 36
Atomic Weight: 83.798
Melting Point: 115.79 K
Boiling Point: 119.93 K
Density: 1 part per million
Phase at Room Temperature: Gas
Element Classification: Non-metal
Period Number: 4
Group Number: 18
Group Name: Noble Gas
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The isotope krypton 86 has a line in its atomic spectrum that is now the standard measure of length : 1 meter is defined as exactly 1,650,763.73 wavelengths of this line.


Krypton was discovered on May 30, 1898 by Sir William Ramsay, a Scottish chemist, and Morris M. Travers, an English chemist, while studying liquefied air. Small amounts of liquid krypton remained behind after the more volatile components of liquid air had boiled away. Krypton is present in the air at about 1 ppm and the atmosphere of Mars also contains a little (about 0.3 ppm). Krypton might be one of the rarest gases in the atmosphere, but in total there are more than 15 billion tonnes of this metal circulating in the planet, of which only about 8 tonnes a year are extracted, via liquid air.

It is characterised by its brilliant green and orange spectral lines. The spectral lines of krypton are easily produced and some are very sharp. In 1960 it was internationally agreed that the fundamental unit of length, the meter, should be defined as 1 m = 1,650,763.73 wavelengths (in vacuo) of the orange-red line of Kr-33.

Under normal conditions krypton is colorless, odorless, fairly expensive gas. Solid krypton is a white crystalline substance with a face-centered cubic structure which is common to all the "rare gases". Krypton difluoride, KrF2, has been prepared in gram quantities and can be made by several methods. other compounds are unstable, unless isolated in a matrix at very low temperatures.

The high cost of obtaining krypton from the air has limited its practical applications. Krypton is used in some types of photographic flashes used in high speed photography. Some fluorescent light bulbs are filled with a mixture of krypton and argon gases. Krypton gas is also combined with other gases to make luminous signs that glow with a greenish-yellow light.

Once thought to be completely inert, krypton is now known to form a few compounds. Krypton difluoride (KrF2) is the easiest krypton compound to make and gram amounts of it have been produced.

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.

Besides the world of science, in the DC Comics universe, Krypton is a fictional planet. No longer in existence, it is the native world of the super-heroes Superman and, in some tellings, Supergirl, and Krypto the "super dog". Kryptonians were the dominant people of Krypton. Kryptonite weakens Superman.

The planet was created by Jerry Siegel and Joe Shuster, and was first referred to in Action Comics #1 (June 1938); the planet was given its first full-fledged appearance in Superman #1 (1939). (More at



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