What are oxidation number rules?

Oxidation number rules help determine the oxidation state of elements in a compound. One rule is that the total oxidation numbers of all elements in a compound must equal the overall charge of the compound. In a neutral molecule or atom, this sum is zero. For polyatomic ions, the sum of the oxidation numbers must equal the charge of the ion. For monatomic ions, the oxidation number corresponds directly to their charge. Another rule is that in free elements, each atom has an oxidation number of zero. Halogens have negative oxidation numbers when forming halide compounds but can have positive oxidation numbers when combined with oxygen. Other rules include that alkali metals always have an oxidation number of +1, and alkaline earth metals always have an oxidation number of +2. Additionally, fluorine always has an oxidation number of -1 in its compounds. Oxygen usually has an oxidation number of -2, except in hydrogen peroxide or peroxide ions, where it has an oxidation number of -1. Hydrogen generally has an oxidation number of +1, but it is -1 when bonded to metals.