In the compound Al2O3 aluminum has an oxidation number of 3 while oxygen's oxidation number is .?

In the compound Al2O3, aluminium has an oxidation number of +3, while oxygen's oxidation number is __-2 ____.

For aluminium oxide (Al2O3) to form the ionic charges MUST balance.

Hence For the 2 aluminiums

it is 2 x 3 = +6

For the 3 oxygens

it is 3 X -2 = -6

+6 -6 = 0

So the charges balance, hence Al2O3 is neutrally charged compound and NOT an ion.