An Overview about the Chemical Element Krypton


Symbol: Kr

Atomic Number: 36

Atomic Mass: 83.798 amu (atomic mass units)

Melting Point: minus 157.2 C (115.950005 K, minus 250.95999 F)

Boiling Point: minus 153.4 C (119.75001 K, minus 244.12 F)

Number of Protons: 36

Number of Electrons: 36

Number of Neutrons: 48

Classification: Noble Gas

Crystal Structure: Cubic

Density @ 293 K: 0.00374 grams per cubic centimeter

Color: Colorless

Krypton was discovered on 30 May 1898 by the Scottish chemist Sir William Ramsay assisted by his student Morris M. Travers. They were studying the constituents of liquefied air. The two scientists first boiled away many of the other gases such as carbon dioxide, oxygen, argon, helium and nitrogen from their liquid air sample. After removing most of the gases they examined the still liquid residue which contained the krypton. The same methodology also allowed the scientists to discover two other noble gases, neon and xenon, in the same year. Krypton gets its name from the Greek word “Kryptos” which means hidden.

Noble gases were once believed to be completely inert but now some compounds have been synthesized. A number of grams of one of these compounds, krypton difluoride, have been produced. Krypton difluoride is also the easiest to make of krypton’s’ few known compounds. The element produces characteristic brilliant green and orange spectral lines.

There are six naturally occurring isotopes of krypton five of which are stable and the other has an extremely long half life. The most common isotope is krypton-84 which makes up 57% of the total. The least common of the naturally occurring isotopes making up only 0.35% of the total is krypton-78. Krypton-86, a naturally occurring isotope, was used to define the length of a meter when it became the international unit of length in1960. A meter is defined as1650763.73 wavelengths (in vacuo) of the orange-red line of Krypton-86. In addition to these natural isotopes krypton has 30 unstable isotopes with half lives ranging from 150 nanoseconds to 229000 years.

Krypton is produced as a byproduct from the separation of gases from liquid air. As it is only present at one part per million in the atmosphere its production is small and the gas is expensive. Krypton has a number of uses that make its production worthwhile.

* Luminous signs with a green yellow color often have krypton as one of their constituent gases.

* It is used in specialized flash bulbs for high speed photography.

* Sometimes used in combination with the noble gas argon in fluorescent light bulbs.