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Rules for Determining Oxidation Number

Oxidation Number: A number assigned to an atom in a molecular compound or molecular ion that indicates the general distribution of electrons among the bonded atoms.
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The oxidation number of any uncombined element...
is 0.
The oxidation number of a monatomic ion...
equals the charge on the ion.
The more electronegative element in a binary compound...
is assigned the number equal to the charge it would have if it were an ion.
The oxidation number of fluorine in a compound...
is always -1.
Oxygen has an oxidation number of -2 unless...
it is combined with F, when it is +2, or it is in a peroxide, when it is -1.
In compounds, the elements of groups 1 and 2 as well as aluminum...
have oxidation numbers of +1, +2, and +3, respectively.
The oxidation state of hydrogen in most of its compounds is +1 unless...
it is combined with a metal, in which case it is -1.
The sum of the oxidation numbers of all atoms in a neutral compound...
is 0.
The sum of the oxidation numbers of all atoms in a polyatomic ion...
equals the charge of the ion.