oxidation number


oxidation number
a number assigned to each atom in a molecule or ion that represents the number of electrons theoretically gained (positive oxidation numbers) or lost (negative numbers) in converting the atom to the elemental form. Oxidation numbers are assigned according to the following rules. The oxidation number of atoms in an elemental form is zero, and the oxidation number of a monatomic ion equals the ionic charge. Group I and Group II metals always have oxidation numbers of +1 and +2, respectively. Fluorine always has an oxidation number of −1; oxygen always of −2, except in peroxides and superoxides (where it is −1) and in compounds containing OF bonds. Hydrogen always has an oxidation number of +1, except in metal hydrides (where it is −1). Oxidation numbers are assigned to other atoms so that the sum for all atoms in a neutral compound equals zero and the sum for all atoms in a polyatomic ion equals the ionic charge. Called also oxidation state.

Medical dictionary. 2011.

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