Oxidation State Practice

Rule 1: For pure elements (unbonded or only bonded with itself), each atom has an oxidation number of zero. 

Rule 2: Monatomic (single) ions have oxidation numbers equal to their charge.

Rule 3: Oxygen’s oxidation number is -2 except when in peroxides (such as H₂0₂), where it is -1.

Rule 4: Hydrogen’s oxidation number is +1, except for when bonded to metals as the hydride ion forming ionic compounds. 

Rule 5: Fluorine (F) has an oxidation number of -1 in ALL of its compounds 

Rule 6: Halogens (Cl, Br, I) have negative oxidation numbers when they form halide compounds. When combined with oxygen, they have positive numbers, except for F. 

Rule 7: In a neutral atom or molecule, the sum of the oxidation numbers must be 0. In a polyatomic ion, the sum of the oxidation numbers of all the atoms in the ion must equal the charge on the ion