Oxidation Number Assignments

The determination of the oxidation number (or oxidation state) of chemical compounds can be made by following a few simple rules.

1. The oxidation numbers of an atom or the atoms in a neutral molecule must add up to zero.
   
2. If an atom or molecule is ionic its oxidation number must add up to its overall charge.
   
3. Alkali metal atoms (Group I) have an oxidation number equal to +1 within compounds. Alkali earth atoms (Group II) have an oxidation number of +2 within compounds.
   
4. Fluorine always has a -1 oxidation number within compounds.
   
5. All halogens (besides fluorine) have a -1 oxidation number in compounds, except when with oxygen or other halogens where their oxidation numbers can be positive.
   
6. Hydrogen is always assigned a +1 oxidation number in compounds, except in metal hydrides (e.g. LiH) where the previous rules apply. In the case of LiH lithium is assigned a +2 charge (rule C) leaving hydrogen to neutralize the compound with a -2 charge.
   
7. Oxygen is assigned an oxidation number of -2 in compounds, with two exceptions...

1	Fluorine's oxidation number always takes precedence.
2	Oxygen oxygen bonds follow previous rules, meaning other assignments take place first leaving oxygen to neutralize the charge.
2(a)	The oxygen has an oxidation number of -1 in peroxide compounds

Examples: (The blue colours are a positive oxidation state, the red colours are a negative oxidation state, relevant to the atoms underneath them.)