- Atoms in elemental form have an oxidation number of zero.
- Single-atom (monoatomic) ions have an oxidation number equal to their charge.
- In a neutral compound, oxidation numbers add up to zero. In a charged compound, oxidation numbers add up to the compound’s charge.
- In compounds, oxygen usually has an oxidation number of –2, in which its oxidation number is –1.
- In compounds, hydrogen has an oxidation number of +1 when it bonds to nonmetals and an oxidation number of –1 when it bonds to metals.
- In compounds
Group 1 atoms (alkali
metals) have oxidation number +1.
Group 2 atoms (alkaline
earth metals) have oxidation number +2.
Group 3 atoms have oxidation
number +3.
Group 17 atoms (halogens)
usually have oxidation number –1.