- Krypton (Kr) is a noble gas with atomic number 36, located in Group 18 of the periodic table between argon and xenon.
- It is colorless, odorless, tasteless, and chemically inert under standard conditions, though it can form a few compounds under extreme conditions.
- Krypton has eight valence electrons—two in the 4s subshell, six in the 4p subshell—giving it a stable electron configuration and minimal chemical reactivity. Its atomic structure consists of thirty-six protons, typically forty-eight neutrons, and thirty-six electrons arranged in four shells.
- Naturally occurring krypton consists of six stable isotopes: krypton-78 (⁷⁸Kr, 0.35%), krypton-80 (⁸⁰Kr, 2.25%), krypton-82 (⁸²Kr, 11.6%), krypton-83 (⁸³Kr, 11.5%), krypton-84 (⁸⁴Kr, 57.0%), and krypton-86 (⁸⁶Kr, 17.3%), along with trace radioactive isotopes produced in nuclear processes.
- Krypton is rare in Earth’s atmosphere, making up only about 1.14 parts per million by volume. It is obtained commercially by fractional distillation of liquefied air, where it is separated from nitrogen, oxygen, and other gases. Krypton can also be recovered as a by-product of liquefied natural gas processing.
- The element was discovered in 1898 by British chemists Sir William Ramsay and Morris Travers during their systematic study of liquefied air. They identified krypton in the residue remaining after most of the nitrogen, oxygen, and argon had been removed. The name comes from the Greek word kryptos, meaning “hidden,” reflecting its elusive presence in the atmosphere.
- Because of its scarcity, krypton has relatively few large-scale applications, but it has specialized uses where its properties are valuable. Krypton is used in high-performance lighting, such as airport runway lights, photographic flashes, and high-intensity discharge lamps, because krypton-filled bulbs have higher efficiency and longer life compared to argon-filled ones. Krypton gas is also used in combination with other noble gases in plasma displays and fluorescent lamps to produce bright white light.
- In scientific research, the radioactive isotope krypton-85 (⁸⁵Kr) is used as a tracer in environmental studies and for measuring air and water movement, though its presence in the atmosphere is also monitored as an indicator of nuclear fuel reprocessing activities. Krypton is used in certain laser systems, notably the krypton ion laser, which emits intense light in the visible spectrum, and in excimer lasers when combined with fluorine (KrF) for applications in microlithography and laser surgery.
- Chemically, krypton is highly unreactive, but in 1962, the first krypton compound—krypton difluoride (KrF₂)—was synthesized under highly controlled laboratory conditions, proving that even noble gases can form stable compounds with strong oxidizers like fluorine. Such compounds have niche uses in chemical synthesis and research.
- Biologically, krypton has no known role in living organisms and is considered non-toxic. It is an asphyxiant in high concentrations, simply by displacing oxygen in enclosed spaces.
- From an environmental perspective, krypton is not considered a pollutant in its stable form, though krypton-85, a radioactive isotope with a half-life of about 10.7 years, can accumulate in the atmosphere from human activities such as nuclear reprocessing. Its long atmospheric lifetime makes it useful for scientific tracking but also a marker of human nuclear activity.
