Try:
KMnO4
| Element | Atoms | Oxidation number | Total | Why |
|---|---|---|---|---|
| K | 1 | +1 | +1 | Group 1 metals are +1 in compounds. |
| Mn | 1 | +7 | +7 | Solved so all oxidation numbers add up to the overall charge. |
| O | 4 | −2 | −8 | Oxygen is usually −2. |
Check: the totals add up to 0 for a neutral compound.
How it works
The standard rules are applied in priority order — fluorine, group 1, group 2, hydrogen, oxygen, then chlorine, bromine and iodine — and the one remaining element is solved so everything adds up to the charge. When two rules conflict, the lower-priority element gives way, which is what makes peroxides (H₂O₂), superoxides (KO₂) and OF₂ come out right.
If two or more elements have no fixed rule (like copper and sulfur in CuSO₄), the calculator tries combinations of their common oxidation states and keeps those that balance. Results are exact fractions, so mixed-valence compounds show a true average rather than a rounded decimal.
Frequently asked questions
- What is an oxidation number?
- The charge an atom would have if every bond in the compound were fully ionic, with the shared electrons given to the more electronegative atom. It is bookkeeping, not a real charge, and it is how chemists track which atoms are oxidized and reduced in a reaction.
- What are the rules for assigning oxidation numbers?
- An uncombined element is 0; a monatomic ion equals its charge; fluorine is −1; group 1 metals are +1 and group 2 metals +2; hydrogen is +1 (−1 in metal hydrides); oxygen is −2 (except in peroxides, superoxides and with fluorine); and all oxidation numbers add up to the overall charge.
- Why is oxygen −1 in hydrogen peroxide?
- In H₂O₂ the two hydrogens are +1 each, and the molecule is neutral, so the two oxygens must share −2 between them: −1 each. The hydrogen rule outranks the oxygen rule, which is why the calculator solves oxygen last here.
- Can an oxidation number be a fraction?
- As an average, yes. In Fe₃O₄ the three irons total +8, averaging +8/3 — in reality one iron is +2 and two are +3. Fractional results always mean the atoms of that element are in different states.
Related
Advertisement