Calcium: calcium oxide

calcium oxide is known by the following synonyms:

  • calcium oxide
  • calcium(II) oxide
  • lime

The oxidation number of calcium in calcium oxide is 2.

  • Formula: CaO
  • Hill system formula: Ca1O1
  • CAS registry number: [1305-78-8]
  • Formula weight: 56.077
  • Class: oxide
  • Colour: white or pale grey
  • Appearance: crystalline solid
  • Melting point: 2900 °C
  • Boiling point:
  • Density: 3340 kg m-3


Calcium oxide can be made by the calcination (heating) of chalk or calcium hydroxide.

CaCO3(s) (heat) → CaO(s)

Ca(OH)2(s) (heat) → CaO(s) + H2O(l)

Solid state structure

  • Geometry of calcium: 6 coordinate: octahedral
  • Prototypical structure: NaCl (rock salt)

Crystal structure of calcium oxide

Element analysis

Element percentages in calcium oxide
Element %
Ca 71.47
O 28.53

Isotope pattern for CaO

THe chart below shows the calculated isotope pattern for the formula CaO 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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