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Krypton

Noble Gas

What is Krypton?

Krypton is a chemical element, inert gas, or noble gas of Group 18 of the periodic table with symbol Kr and atomic number 36. It occurs in trace amounts in the earth’s environment and is used with other rare gases in fluorescent lamps. Krypton is a colorless, odorless, tasteless, monoatomic gas that forms a few numbers of chemical compounds with fluorine. Due to filled valence orbital, the oxidation number or state is zero but with fluorine, krypton shows a +2 oxidation state also. It is placed in the p-block of the periodic table with group members helium, neon, argon, xenon, and radon.

Position of noble gas or inert gas Krypton on the periodic table elements

Discovery of krypton

Krypton was discovered in 1898 by the British chemist’s Sir William Ramsay and Morris W. Travers and the name of the gas derived from the Greek latter kryptos meaning hidden. The electromagnetic spectrum analysis of Krypton is characterized by several sharp emissions of green and yellow lines in the spectrum. In solid-state, it forms a face-centered cubic crystal lattice, and the cubic close-packed structure being the most space-economizing.

Properties of krypton

Krypton (Kr), chemical element or noble gas of Group 18 of periodic table with properties, compounds and uses

The rare gas, Kr has valence shell electron configuration [Ar] 3d10 4s2 3p6, and heat capacity ratio (Cp/Cv) close to 1.66. It occurs in the earth’s atmosphere to the extent of 0.0001 percent and is obtained by low-temperature distillation of liquid air.

Properties of Krypton
Chemical symbol Kr
Atomic number 36
Atomic weight 83.80
Electronic configuration [Ar] 3d10 4s2 4p6
Meting point -157.37 °C
Boiling point -153.41 °C
Density 3.749 g/L
Molar heat capacity 20.95 J mol-1 K-1
Oxidation state 0, +2
Electronegativity 3.00 (Pauling scale)
Ionization energy 1st – 1350.8 kJ/mol
2nd – 2350.4 kJ/mol
Crystal structure ​face-centered cubic (fcc)
Critical temperature 209.48 K

Isotopes of Kr

Naturally occurring krypton has six isotopes like 84Kr (57 percent), 86Kr (17.3 percent), 82Kr (11.6 percent), 83Kr (11.5 percent), 80Kr (2.25 percent), and 78Kr (0.35 percent). It also formed about thirty-six unstable radioactive isotopes which are obtained by nuclear fission of uranium or any other nuclear reaction. 78Kr (half-life 9.2×1021 years) is a stable isotope among all isotopes that formed by radioactive decay reaction. 85Kr (half-life 10.76 years) is prepared normally by nuclear fission of uranium and plutonium which is also emitted during the reprocessing of nuclear power reactors. The radioactive isotopes 81Kr used dating ground water.

Chemical Compounds

The chemistry of krypton or other noble gases like helium, neon, and argon is different from other elements of the periodic table due to their filled valence shell configuration and high ionization energy. But it formed a few unstable chemical compounds with fluorine along with clathrates or cage compounds. The clathrates or cage compounds are formed mainly with water and para-quinol by trapping krypton molecule in the hydrogen bonding network.

Krypton difluoride

The only known unstable halide compound is krypton difluoride (KrF2). The rare gas compound, KrF2 may be prepared by passing an electric discharge through a mixture of krypton and fluorine molecule at low pressure in a U-tube immersed with liquid oxygen. It is also formed by the action of OF2 on Kr in presence of sunlight. The chemical compound KrF2 less stable than XeF2 and dissociated into Kr and F2 at room temperature. KrF2 uses a fluorinating agent that fluorinated xenon or noble metals like silver and gold. A mixture of KrF2 and XeF2 fluorinated many trivalent lanthanide compounds like LnF4, LnF7-3, and LnOF2, where Ln = Ce, Pr, Nd, Tb, and Dy.

Krypton difluoride structure

A liner KrF2 has a similar structure to that of XeF2 with the Kr-F bond distance of 189 pm. The Kr-F bond energy is about 50 kJ mol-1, which is the lowest value of bond energy for chemical bonding formed by any element with fluorine. It bonded to nitrogen in the salt HCHKrF2+[AsF6] which was made by reacting KrF2 with HCN+[AsF6] in hydrogen fluoride solution. Other nitrile adducts of krypton are also known, for example [RC≡NKrF]+, where R = Me, CF3, C2F5, and n-C3F5. Kr-O bond also presents in the thermally unstable compound like Kr(OTeF5)2.

Uses of Krypton

Krypton element tube or lamp, sign, uses and properties

  • Krypton is widely used in electronics like fluorescent lamps, tubes. When a passage of electricity passes through a glass tube containing krypton, it emitted a bluish-white light which is widely used in the flash lamp of high-speed photography. It is mixed with mercury to make the glow of bright greenish-blue light. In energy efficient fluorescent lamps, we used a mixture of krypton and argon to save power.
  • The unstable chemical compound, krypton fluoride (KrF2) used in laser for different types of experiments of nuclear fusion.
  • Krypton and its isotopes are also used in different types of research of particle physics and chemistry, magnetic resonance imaging, and nuclear medicine.