page_title: Krypton
section_title: Chemistry
hierarchical_section_title: Krypton / Characteristics / Chemistry
caption_attribution_description: Face-centered cubic structure of Kr(H2)4 at 11.24 GPa. Isolated krypton octahedra (green) are located at each lattice point. Grey spheres represent rotationally disordered hydrogen molecules.
context_page_description: Krypton is a chemical element with the symbol Kr and atomic number 36. It is a colorless, odorless, tasteless noble gas that occurs in trace amounts in the atmosphere and is often used with other rare gases in fluorescent lamps. With rare exceptions, krypton is chemically inert.
  Krypton, like the other noble gases, is used in lighting and photography. Krypton light has many spectral lines, and krypton plasma is useful in bright, high-powered gas lasers, each of which resonates and amplifies a single spectral line. Krypton fluoride also makes a useful laser medium. From 1960 to 1983, the official length of a meter was defined by the 606-nanometer wavelength of the orange spectral line of krypton-86, because of the high power and relative ease of operation of krypton discharge tubes.
context_section_description: Like the other noble gases, krypton is chemically highly unreactive. The rather restricted chemistry of krypton in the +2 oxidation state parallels that of the neighboring element bromine in the +1 oxidation state; due to the scandide contraction it is difficult to oxidize the 4p elements to their group oxidation states. Until the 1960s no noble gas compounds had been synthesized.
  However, following the first successful synthesis of xenon compounds in 1962, synthesis of krypton difluoride (KrF
  ₂) was reported in 1963. In the same year, KrF
  ₄ was reported by Grosse, et al., but was subsequently shown to be a mistaken identification. Under extreme conditions, krypton reacts with fluorine to form KrF₂ according to the following equation:
  Kr + F₂ → KrF₂
  Krypton gas in a krypton fluoride laser absorbs energy from a source, causing the krypton to react with fluorine gas, producing the exciplex krypton fluoride, a temporary complex in an excited energy state:
  2 Kr + F
  ₂ → 2 KrF
  The complex can undergo spontaneous or stimulated emission, reducing its energy state to a metastable, but highly repulsive ground state. The ground state complex quickly dissociates into unbound atoms:
  2 KrF → 2 Kr + F
  ₂
  The result is an exciplex laser which radiates energy at 248 nm, near the ultraviolet portion of the spectrum, corresponding with the energy difference between the ground state and the excited state of the complex.
  Compounds with krypton bonded to atoms other than fluorine have also been discovered. There are also unverified reports of a barium salt of a krypton oxoacid. ArKr⁺ and KrH⁺ polyatomic ions have been investigated and there is evidence for KrXe or KrXe⁺.
  The reaction of KrF
  ₂ with B(OTeF
  ₅)
  ₃ produces an unstable compound, Kr(OTeF
  ₅)
  ₂, that contains a krypton-oxygen bond. A krypton-nitrogen bond is found in the cation [HC≡N–Kr–F]⁺
  , produced by the reaction of KrF
  ₂ with [HC≡NH]⁺
  [AsF⁻
  ₆] below −50 °C. HKrCN and HKrC≡CH (krypton hydride-cyanide and hydrokryptoacetylene) were reported to be stable up to 40 K.
  Krypton hydride (Kr(H₂)₄) crystals can be grown at pressures above 5 GPa. They have a face-centered cubic structure where krypton octahedra are surrounded by randomly oriented hydrogen molecules.
caption: Structure of Kr(H2)4. Krypton octahedra (green) are surrounded by randomly oriented hydrogen molecules.[22]
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