What is the oxidation number of each element in the compound SiO2 (sand)?
Si: +4 O:-2
The oxidation of oxygen is always -2, and since there are two of them, you get -4. That means that Si has to be +4 to balance
Oxidation number is the charge left on the central atom when all the bonding pairs are taken away, with the charge going to the most electronegative atom.
The sum of the oxidation equals the charge on the "molecule"; oxygen usually has an oxidation number of