Nickel(II) oxide

Nickel(II) oxide

Nickel(II) oxide
Other names nickelous oxide
nickel monoxide
Molecular formula NiO
Molar mass 74.69 g/mol
Appearance green crystalline solid
CAS number [1313-99-1]
Density and phase 6.67 g/cm3, solid
Solubility in water negligible
Melting point 1984°C
Boiling point ?
EU classification not listed
NFPA 704
Except where noted otherwise, data are given for
materials in their standard state (at 25 °C, 100 kPa)
Chemical infobox

Nickel(II) oxide is the chemical compound with the formula NiO. It is notable as being the only well characterised oxide of nickel although there have been many reports of others (nickel(III) oxide, Ni2O3, and nickel dioxide, NiO2).

The mineralogical form of NiO, bunsenite, is very rare. It was suspected for causing green colour of chrysoprase, but later it was rejected.

Preparation and properties

The best method of preparation is through pyrolysis of a nickel(II) compounds such as Ni(OH)2, Ni(NO3)2, and NiCO3, which yield a light green powder.Synthesis from the elements by heating the metal in oxygen can yield grey to black powders which may indicate nonstoichiometry. NiO is a basic oxide.


NiO adopts the NaCl structure, with octahedral Ni(II) and O2− sites. Like many other binary metal oxides, NiO is often non-stoichiometric, meaning that the Ni:O ratio deviates from 1:1.


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