Oxidation numbers

Oxidation numbers tell you how many electrons atoms have

The number tell you how many electrons an atom has donated or accepted to form an ion or to form part of compound.

Monotonic ions is same as charge. Molecular ions, sum of all numbers is same as overall charge.

Oxidation numbers must know

Oxygen -2 except in peroxides (O₂^-2) where it’s -1 and O₂ where it’s 0.

Hydrogen +1 except in metal hydrides where it’s -1 and H₂ where it’s 0.

Roman numerals tell you the oxidation number

In iron(II) irons oxidation number is +2

In iron(III) irons oxidation number is +3

-ate compounds contain oxygen and another element

Sulfate(VI) ions, sulfur has oxidation number of +6 - this is the SO₄^2- ion.