How do you find a Oxidation number

An oxidation number is the charge of the ion that would form if a covalent molecule was ionic. Oxidation numbers exist for covalent compounds, as ions are not formed.

The oxidation number is determined by the respective electronegativity of the atoms involved. A more electronegative element will always have a negative oxidation number. In the compound, all the oxidation numbers must add up to 0. Oxidation numbers of elements can vary between compunds.

A few rules to follow about oxidation numbers

Fluorine will always be - 1

Oxygen will be - 2 unless in a compound with fluorine

Hydrogen is usually + 1

A few examples

HF (Hydrogen flouride) Oxy number of H = + 1 and F = - 1

H2O Oxy number of H = + 1 and O = - 2

NH3 Oxy of H = + 1 and since there are 3 Hydrogens each with an oxidation number of + 1 N must have an oxy number of - 3 for the overall oxidation number of the compound to be 0.

H2SO4 Oxy number of H = + 1 O=-2 When adding up the hydrogen and oxygen oxidation numbers (1 + 1 - 2 - 2 - 2 - 2) we are left with - 6 thus S must have an oxidation number of + 6 for the overall number to be 0.

NO2 Oxidation number of O = - 2 there are 2 oxygens leaving us with - 4 thus N must have an Oxy number of + 4 for the overall number to be 0.