How do I find the oxidation numbers of individual elements in an ion or molecule?

1 Answer
Oct 24, 2016

The sum of the oxidation numbers ALWAYS equal the charge on the ion, OR on the molecule....

Explanation:

And of course, if it is a neutral molecule, the sum of the constituent elemental oxidation numbers is ZERO.

Nitrogen oxide, NO, is a neutral molecule, and thus the sum of the oxidation numbers must be zero. The oxidation number of O is normally II, and it is here. The oxidation number of nitrogen must of course be +II, because the sum of the oxidation numbers must equal the neutral charge on the molecule. For NO2, the oxidation number of N must be +IV. And of course, for N2O5 the oxidation number of nitrogen is?

For nitrous oxide, N2O, the oxidation number of O is still II. And for this neutral molecule, the oxidation number of N is +I, i.e. 1+12=0 as required.

Given all this, can you tell me the oxidation number of the metal in Cr2O27?