Krypton Periodic Table Facts
Krypton (Kr), chemical element, inert gas, or noble gas of Group 18 of the periodic table occur in trace amounts in the earth’s atmosphere and are used with other rare gases in fluorescent lamps. It is a colorless, odorless, tasteless, monoatomic gas that forms a few numbers of chemical compounds with fluorine. Krypton was discovered in 1898 by the British chemists Sir William Ramsay and Morris W. Travers and name 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.
The rare gas, krypton has the chemical symbol Kr, atomic number 36, atomic weight 83.80, melting point -157.37 °C, boiling point -153.41 °C, valence shell electron configuration [Ar] 3d10 4s2 3p6, and heat capacity ratio (Cp/Cv) close to 1.66. Due to filled valence orbital, the oxidation number or state is zero but with fluorine, krypton shows a +2 oxidation state also. It occurs in the earth’s atmosphere to the extent of 0.0001 percent and is obtained by low-temperature distillation of liquid air.
Isotopes of Krypton
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.
Chemistry and 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 krypton 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.
The only known unstable halide compound is krypton fluoride (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.
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. Krypton 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 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.