Caesium: dicaesium oxide

dicaesium oxide is known by the following synonyms:

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

The oxidation number of caesium in dicaesium oxide is 1.

  • Formula: Cs2O
  • Hill system formula: Cs2O1
  • CAS registry number: [20281-00-9]
  • Formula weight: 281.81
  • Class: oxide
  • Colour: yellow to orange
  • Appearance: crystalline solid
  • Melting point: 490°C
  • Boiling point:
  • Density: 4650 kg m-3


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

Element analysis

Element percentages in dicaesium oxide
Element %
Cs 94.32
O 5.68

Isotope pattern for Cs2O

THe chart below shows the calculated isotope pattern for the formula Cs2O with the most intense ion set to 100%.


Coming soon...


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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