Definition of oxidation number in US English:

oxidation number

(also oxidation state)


  • A number assigned to an element in chemical combination which represents the number of electrons lost (or gained, if the number is negative), by an atom of that element in the compound.

    • ‘A negative oxidation state indicates that an atom can undergo reduction, i.e., gain electrons.’
    • ‘The oxidation number for both oxygen atoms in hydrogen peroxide is - 1.’
    • ‘The term valence can also refer to the charge or oxidation number on an atom.’
    • ‘The electronegativity is lower for a given oxidation state in an anion than it is in a neutral molecule.’
    • ‘Electrons are assigned to atoms in covalent and ionic compounds and the oxidation number of each atom is determined.’