page_title: Caesium
section_title: Oxides
hierarchical_section_title: Caesium / Characteristics / Compounds / Oxides
caption_attribution_description: Cs11O3 clusetr in Cesium suboxides
context_page_description: Caesium is a chemical element with the symbol Cs and atomic number 55. It is a soft, silvery-golden alkali metal with a melting point of 28.5 °C, which makes it one of only five elemental metals that are liquid at or near room temperature. Caesium has physical and chemical properties similar to those of rubidium and potassium. The most reactive of all metals, it is pyrophoric and reacts with water even at −116 °C. It is the least electronegative element, with a value of 0.79 on the Pauling scale. It has only one stable isotope, caesium-133. Caesium is mined mostly from pollucite, while the radioisotopes, especially caesium-137, a fission product, are extracted from waste produced by nuclear reactors.
  The German chemist Robert Bunsen and physicist Gustav Kirchhoff discovered caesium in 1860 by the newly developed method of flame spectroscopy. The first small-scale applications for caesium were as a "getter" in vacuum tubes and in photoelectric cells.
context_section_description: More so than the other alkali metals, caesium forms numerous binary compounds with oxygen. When caesium burns in air, the superoxide CsO
  ₂ is the main product. The "normal" caesium oxide (Cs
  ₂O) forms yellow-orange hexagonal crystals, and is the only oxide of the anti-CdCl
  ₂ type. It vaporizes at 250 °C (482 °F), and decomposes to caesium metal and the peroxide Cs
  ₂O
  ₂ at temperatures above 400 °C (752 °F). In addition to the superoxide and the ozonide CsO
  ₃, several brightly coloured suboxides have also been studied. These include Cs
  ₇O, Cs
  ₄O, Cs
  ₁₁O
  ₃, Cs
  ₃O (dark-green), CsO, Cs
  ₃O
  ₂, as well as Cs
  ₇O
  ₂. The latter may be heated in a vacuum to generate Cs
  ₂O. Binary compounds with sulfur, selenium, and tellurium also exist.
caption: Cs
  11O
  3 cluster
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