Rules for assigning oxidation numbers. Sum of all oxidation numbers = overall charge.
| Rule | Example | Ox. # |
|---|---|---|
| Free element | O2, Fe, N2 | 0 |
| Monoatomic ion | Na+, Cl-, Fe2+ | Ion charge |
| Hydrogen (most compounds) | H2O, HCl, NH3 | +1 |
| Hydrogen (metal hydrides) | NaH, CaH2 | -1 |
| Oxygen (most compounds) | H2O, CO2, Fe2O3 | -2 |
| Oxygen (peroxides) | H2O2, Na2O2 | -1 |
| Fluorine (always) | HF, NaF, CF4 | -1 |
| Group 1 metals | NaCl, KOH, Li2O | +1 |
| Group 2 metals | MgO, CaCl2, BaSO4 | +2 |
| Aluminum | Al2O3, AlCl3 | +3 |
Worked Examples
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About Oxidation #
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