Oxidation Numbers

Element by itself like O_2, Fe, or Cl_2

0

Group 1 metals, like Na and K

+1

Group 2 metals, like Ca and Mg

+2

Hydrogen in most compounds

+1

Oxygen in most compounds

−2

Fluorine in compounds

−1

Single-atom ion, like Fe^3+

Equal to its charge

Neutral compound

All oxidation numbers add to 0

Polyatomic ion

All oxidation numbers add to the ion's charge

Exceptions to remember:

oxygen is −1 in peroxides such as H_2O_2, and hydrogen is −1 in metal hydrides such as NaH