# How can I assign oxidation numbers to each of the atoms?

Jun 24, 2014

Without knowing which atoms in particular, here are a few rules:

1. Solid metals and diatomic gases always have an oxidation number (ON) of zero.
2. Alkali metals (column #1) always have an oxidation number of +1
3. Halogens, following a metal, have an ON of -1

4. Hydrogen, acting like a metal, will have a charge of +1 and oxygen will have a charge of -2

5. Peroxides made with a column 1 metal and oxygen for ex: ${K}_{2} {O}_{2}$, or ${H}_{2} {O}_{2}$, the oxygen will have a -1 charge. There are peroxides with column 2 metals, for example $M g {O}_{2}$, the Oxygen will still have a charge of -1.

6. Metal hydrides, made with a metal first and a hydrogen last, for example, $N a H$, the H will have a charge of -1

7. Count the polyatomic atoms on the back of the high school periodic table, as what they are to help determine any other atom in a formula.