1. The oxidation number of a free element is always 0.
2. The oxidation number of a mono-atomic ion is equal to the charge of the ion.
3. For a given bond, X-Y, the bond is split to give X+ and Y−, where Y is more electronegative than X.
4. The oxidation number of H is +1, but it is -1 in when combined with less electronegative elements.
5. The oxidation number of O in its compounds is usually -2, but it is -1 in peroxides.
6. The oxidation number of a Group 1 element in a compound is +1.
7. The oxidation number of a Group 2 element in a compound is +2.
8. The oxidation number of a Group 17 element in a binary compound is -1.
9. The sum of the oxidation numbers of all of the atoms in a neutral compound is 0.
10. The sum of the oxidation numbers in a polyatomic ion is equal to the charge of the ion.
Now this might be more than you want to know. But the maximum oxidation number of an element is equal to its Group number. Typically we assign oxygen (in its oxides) a −II charge, and fluorine, in it compounds has −I charge.
For potassium permanganate, we got K+MnO−4, i.e. K(+I),Mn(+VII),4×O(−II); the sum of the numbers is ZERO. Why so?
