Calcium compounds: calcium oxide

calcium symbol icon

The calcium in calcium oxide formally is in the oxidation state 2.

Crystal structure of calcium oxide

Calcium oxide

  • Formula as often written: CaO
  • Hill system formula: Ca1O1
  • CAS registry number: [1305-78-8]
  • Formula weight: 56.077
  • Class: oxide


  • calcium oxide
  • calcium(II) oxide
  • lime

Physical properties

  • Colour: white or pale grey
  • Appearance: crystalline solid
  • Melting point: 2900 °C
  • Boiling point:
  • Density: 3340 kg m-3


Coming soon...

Element analysis

Element percentages for the elements in calcium oxide
Element %
Ca 71.47
O 28.53


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

Isotope pattern

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

Formula: Ca1O1

mass  %
56 100.0 __________________________________________________
57 0.0
58 0.9
59 0.1
60 2.2 _
61 0.0
62 0.0
63 0.0
64 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.

WebElements Shop

WebElements now has a WebElements shop at which you can buy periodic table posters, mugs, T-shirts, games, fridge magnets, molecular models, and more.

Periodic Table fridge magnets Periodic Table fridge magnets
Buy our periodic table fridge magnets here

WebElements poster Periodic table t-shirts Periodic table mouse mats Molymod molecular model kits Chemistry educational resources

calcium atomic number