What Is Krypton Gas?
Krypton gas is an element with atomic number 36.
It belongs to group 18 of the periodic table and is classified as a noble or inert gas because of its minimal chemical reactivity. Krypton gas has a boiling point higher than that of oxygen, which makes it a byproduct in the production of air separation gases such as oxygen, nitrogen, and argon. Highly pure krypton gas can be obtained when liquid oxygen containing krypton gas is separated from its components in a purifier.
Uses of Krypton Gas
Krypton gas is widely used as an inert and nonflammable gas because it does not react easily with other substances. A notable application is as an encapsulating gas in lighting and lamps. Krypton gas has low thermal conductivity, which can reduce heat loss through heat dissipation from the filament of a light bulb. It is said to improve lamp efficiency by about 10% compared to argon-filled bulbs. Furthermore, krypton gas, with its high heat insulation properties, is also used as a building material. Windows sealed with krypton gas can increase the heating efficiency of entire indoor spaces.
In advanced fields, krypton fluoride (KrF) is widely used as a light source for etching lasers in semiconductor manufacturing.
Properties of Krypton Gas
Krypton gas has a melting point of -157.2 °C (-251 °F) and a boiling point of -152.9 °C (-243.2 °F). It is a colorless, odorless gas at room temperature and pressure. It is present in air at about 1.14 ppm. It is obtained by the liquefaction of air and fractional distillation.
Krypton gas has a specific gravity of 2.82 at -157 °C (-251 °F). It is a heavy gas and can lower the pitch of a person’s voice when inhaled. It has no valence electrons in its outermost shell, making it chemically stable.
Structure of Krypton Gas
There are 31 known isotopes of krypton gas. In nature, there are five stable isotopes and one radioactive isotope. It can form inclusion compounds with water and hydroquinone. The chemical formulas are Kr – 6H2O and Kr – 3C6H4(OH)2. Crystals of krypton gas (Kr(H2)4) are obtained above 5 GPa. These crystals have a face-centered cubic structure with the octahedron of krypton gas surrounded by randomly oriented hydrogen molecules.
Other Information on Krypton Gas
1. Isotopes of Krypton Gas
81Kr is produced by reactions in the atmosphere. It has a half-life of 250,000 years and is the natural isotopic source of krypton gas. Krypton gas near the water surface is very volatile, and 81Kr is used to date groundwater from 50,000 to 800,000 years.
78Kr is a nuclide in which double electron capture occurs. However, its probability is low and its half-life is estimated to be over 1.1 x 1020 years. 85Kr, an inert radioactive gas, has a half-life of 10.76 years. It is produced by the fission reaction of plutonium or uranium, is manufactured in nuclear reactors, and is released entirely into the environment during the fuel rod reprocessing process.
In the 1940s, the atmospheric concentration of 85Kr was less than 0.001 becquerels per m3 of air. However, the current concentration is more than 1 becquerel in 1 m3 of air. Concentrations are reported to be 30% higher in the Arctic than in the Antarctic. This is because most of the reactors are located in the northern hemisphere. 85Kr becomes 85Rb by beta decay.
2. Compounds of Krypton Gas
Krypton gas is inert, but it can form unstable compounds with fluorine and an oxidation number of +2. Krypton difluoride (KrF2) is a volatile solid and is represented by the chemical formula KrF2. The molecular structure of KrF2 is linear and the Kr-F distance is 188.9 pm. Reaction with strong acids produces cations such as KrF+ and Kr2F3+.
The reaction of KrF2 with B(OTeF5)3 can produce Kr(OTeF5)2, an unstable compound containing a krypton-oxygen bond. Krypton-nitrogen bonds are also found in [HC=N–Kr–F]+ produced by the reaction of KrF2 with [HC=NH]+[AsF6–] below -50°C. HKrCN and HKrC=CH are reported to be stable up to 40K.