Caesium compounds: dicaesium oxide

caesium symbol icon

The caesium in dicaesium oxide formally is in the oxidation state 1.

Crystal structure of dicaesium oxide

Dicaesium oxide

  • Formula as often written: Cs2O
  • Hill system formula: Cs2O1
  • CAS registry number: [20281-00-9]
  • Formula weight: 281.81
  • Class: oxide


  • dicaesium oxide
  • caesium(I) oxide
  • cesium(I) oxide
  • dicesium oxide

Physical properties

  • Colour: yellow to orange
  • Appearance: crystalline solid
  • Melting point: 490°C
  • Boiling point:
  • Density: 4650 kg m-3


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Element analysis

Element percentages for the elements in dicaesium oxide
Element %
Cs 94.32
O 5.68


If caesium is burned in air, the result is mainly formation of orange caesium superoxide, CsO2. The resulting CsO2 can be converted into Cs2O by the careful reaction of CsO2 with caesium metal under nitrogen.

Cs(s) + O2(g) → CsO2(s)

CsO2(s) + 3Cs(s) → 2Cs2O(s)

Solid state structure

  • Geometry of caesium: 3 coordinate: pyramidal
  • Prototypical structure:

Crystal structure of dicaesium oxide

Isotope pattern

What follows is the calculated isotope pattern for the Cs2O unit with the most intense ion set to 100%.

Formula: Cs2O1

mass  %
282 100.0 __________________________________________________
283 0.0
284 0.2


The data on these compounds pages are assembled and adapted from the primary literature and several other sources including the following.

  • R.T. Sanderson in Chemical Periodicity, Reinhold, New York, USA, 1960.
  • N.N. Greenwood and A. Earnshaw in Chemistry of the Elements, 2nd edition, Butterworth, UK, 1997.
  • F.A. Cotton, G. Wilkinson, C.A. Murillo, and M. Bochmann, in Advanced Inorganic Chemistry, John Wiley & Sons, 1999.
  • A.F. Trotman-Dickenson, (ed.) in Comprehensive Inorganic Chemistry, Pergamon, Oxford, UK, 1973.
  • R.W.G. Wyckoff, in Crystal Structures, volume 1, Interscience, John Wiley & Sons, 1963.
  • A.R.West in Basic solid state chemistry Chemistry, John Wiley & Sons, 1999.
  • A.F. Wells in Structural inorganic chemistry, 4th edition, Oxford, UK, 1975.
  • J.D.H. Donnay, (ed.) in Crystal data determinative tables, ACA monograph number 5, American Crystallographic Association, USA, 1963.
  • D.R. Lide, (ed.) in Chemical Rubber Company handbook of chemistry and physics, CRC Press, Boca Raton, Florida, USA, 77th edition, 1996.
  • J.W. Mellor in A comprehensive treatise on inorganic and theoretical chemistry, volumes 1-16, Longmans, London, UK, 1922-1937.
  • J.E. Macintyre (ed.) in Dictionary of inorganic compounds, volumes 1-3, Chapman & Hall, London, UK, 1992.

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caesium atomic number