# Oxidation Number Calculator

Free oxidation number calculator. Determine oxidation states in compounds and ions using standard rules. Step-by-step calculations for chemistry students.

## What this calculates

Calculate the oxidation number (oxidation state) of an element in a compound. Enter the known element, its oxidation state, atom counts, and overall charge to find the unknown oxidation state.

## Inputs

- **Compound Type** — options: Binary Compound (2 elements), Compound with Known Ion, Monatomic Ion — Select the type of compound or species.
- **Overall Charge** — min -10, max 10 — Overall charge of the species (0 for neutral compounds).
- **Known Element** — options: Oxygen (usually -2), Hydrogen (usually +1), Fluorine (always -1), Chlorine (usually -1), Sodium (always +1), Potassium (always +1), Calcium (always +2), Magnesium (always +2), Aluminum (always +3) — Element with a known oxidation state.
- **Known Oxidation State** — min -4, max 7 — The oxidation number of the known element.
- **Known Element Count** — min 1, max 20 — Number of atoms of the known element in the formula.
- **Unknown Element Count** — min 1, max 20 — Number of atoms of the unknown element in the formula.
- **Ion Charge (for monatomic ion)** — min -4, max 7 — For monatomic ions, the charge equals the oxidation number.

## Outputs

- **Unknown Element Oxidation State** — formatted as text — The calculated oxidation number of the unknown element.
- **Rule Applied** — formatted as text — The oxidation state rule used.
- **Calculation** — formatted as text — Step-by-step calculation.

## Frequently Asked Questions

**Q: What is an oxidation number?**

A: An oxidation number (oxidation state) is a number assigned to an atom representing the hypothetical charge it would have if all bonds were completely ionic. It helps track electron transfer in redox reactions.

**Q: What are the basic rules for assigning oxidation numbers?**

A: Key rules: (1) Free elements have oxidation state 0. (2) Monatomic ions have oxidation state equal to their charge. (3) Oxygen is usually -2 (except in peroxides, -1). (4) Hydrogen is usually +1 (except in metal hydrides, -1). (5) Fluorine is always -1. (6) Sum of oxidation states = overall charge.

**Q: Why are oxidation numbers important?**

A: Oxidation numbers are essential for balancing redox equations, identifying which atoms are oxidized (lose electrons) and reduced (gain electrons), and understanding electron transfer in chemical reactions.

**Q: Can oxidation numbers be fractions?**

A: Yes, in some compounds the average oxidation number per atom can be a fraction. For example, in Fe₃O₄ (magnetite), iron has an average oxidation state of +8/3. This indicates mixed oxidation states among the iron atoms.

---

Source: https://vastcalc.com/calculators/chemistry/oxidation-number
Category: Chemistry
Last updated: 2026-04-21