BOILING POINT: −153.22°C
DENSITY: 2.818 g/cm 3
MOST COMMON IONS: None
Krypton (from the Greek word kryptos, meaning "hidden"), is the second heaviest of the noble gases . It was discovered in 1898 by Sir William Ramsay and Morris Travers during their experiments with liquid air, air that has been liquefied by cooling. It has a concentration of 1.14 ppm by volume in Earth's atmosphere. It is present in the Sun and in the atmosphere of Mars.
At room temperature krypton is a colorless, odorless gas. Upon freezing it forms a white crystal with a face-centered cubic structure. In a vacuum discharge tube, it emits primarily a mixture of green and yellow light. During the late twentieth century the wavelength of light corresponding to krypton's 605.78-nanometer (2.4 × 10 −5 -inch) spectral line was the internationally adopted definition of the meter. Krypton gas is used in the manufacture of fluorescence lights and flashlamps used in high-speed photography.
Krypton is produced deep within stars during nucleosynthesis . It has six naturally occurring (i.e., stable) isotopes , the most abundant of which is krypton-84 (57%). Some long-lived radioactive isotopes exist as well. Two of them, krypton-85 (half-life = 10.7 y) and krypton-81 (half-life = 210,000 y) have been used to date well water. Radioactive krypton is produced in fission reactions of heavy elements. Thus, radioactive isotopes of krypton have always formed part of the natural radiation background of Earth's atmosphere.
Although a noble gas, krypton is not entirely unreactive. One krypton compound, krypton difluoride (KrF 2 ), is commercially available in small quantities.
Almqvist, Ebbe (2003). History of Industrial Gases. New York: Kluwer Academic/Plenum Publishers.
Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics, 84th edition. Boca Raton, FL: CRC Press.