Oxidation Number

The oxidation number or oxidation state of an atom in a molecule or a polyatomic ion is the charge it would bear if all its bonds to unlike atoms were ionic bonds.

eg. 1:  Methane



There are no bonds connecting like atoms in the methane molecule.
electronegativity:   C > H



eg. 2:  Acetaldehyde



There is one bond connecting like atoms in the acetaldehyde molecule, the carbon-carbon bond.
electronegativity:   O > C > H



eg. 3:  Nitric acid



There are no bonds connecting like atoms in the nitric acid molecule.
electronegativity:   O > N > H


eg. 4:  Periodate ion



There are no bonds connecting like atoms in the periodate ion.
electronegativity:   O > I



see also oxidation, reduction

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