The bonding triangle shows that bonding is often not purely ionic or covalent, but occurs on a continuum with unequal sharing of electrons

The oxidation state (also called oxidation number) is a number assigned to an atom to show the number of electrons transferred in forming a bond. It is the charge that atom would have if the compound were composed of ions.

Deducing Oxidation States in Compounds

Rules

1. The oxidation state of any free element is zero

2. The sum of oxidation states in a neutral compound is zero

3. The sum of oxidation states in a polyatomic ion equals that charge of the ion

4. Oxidation state of fluorine is -1 in all compounds (NOT F₂)

5. The oxidation state of a group 1 metal is always +1 and the oxidation state of a group 2 metal is +2

6. The oxidation state of oxygen is -2 except in OF₂, where fluorine is more electronegative, so oxygen has an oxidation state of +2, and in peroxides such as H₂O₂ where it is -1

7. The oxidation state of hydrogen is +1 when it is combined with more electronegative elements, and -1 when combined with less electronegative elements. H with a -1 state is called a hydride ion

Naming Oxyanions

Oxyanions are polyatomic ions that include oxygen atoms. When naming oxyanions, the oxidation state of the non-oxygen atom should be included as a roman numeral at the end of the name

In practice, the Roman numeral is omitted for some common oxyanions