Oxidation Number Calculator
Compute oxidation number using validated scientific equations. See step-by-step derivations, unit analysis, and reference values.
Formula
Sum of all oxidation numbers = overall charge of compound/ion
The oxidation number represents the hypothetical charge of an atom if all bonds were ionic. In a neutral compound, oxidation numbers sum to zero. In a polyatomic ion, they sum to the ion charge. Use known oxidation state rules (O = -2, H = +1, etc.) and solve algebraically for unknowns.
Frequently Asked Questions
What are oxidation numbers and why are they important?
Oxidation numbers (or oxidation states) represent the hypothetical charge an atom would have if all bonds were completely ionic. They are essential for balancing redox reactions, identifying which atoms are oxidized or reduced, and naming compounds. Oxidation numbers help track electron transfer in chemical reactions. For example, when iron rusts, Fe goes from oxidation state 0 to +3, indicating it lost electrons (was oxidized), while oxygen goes from 0 to -2 (was reduced).
What are the basic rules for assigning oxidation numbers?
The key rules are: (1) Free elements have oxidation state 0. (2) Monoatomic ions equal their charge. (3) Oxygen is usually -2 (except in peroxides where it is -1). (4) Hydrogen is usually +1 with nonmetals and -1 with metals. (5) Fluorine is always -1. (6) Group 1 metals are always +1, Group 2 are always +2. (7) The sum of oxidation numbers in a neutral compound equals 0, and in a polyatomic ion equals the ion charge. These rules allow you to solve for unknown oxidation states algebraically.
How do you find the oxidation number of an element in a compound?
Assign known oxidation states to all elements with fixed values (such as O = -2, H = +1, alkali metals = +1). Then use the rule that all oxidation numbers must sum to the overall charge (0 for neutral compounds, or the ion charge). Set up an equation: sum of (oxidation state times count for each element) equals total charge, and solve for the unknown. For example, in KMnO4: K is +1, O is -2. So +1 + Mn + 4(-2) = 0, giving Mn = +7.
What is the difference between oxidation number and formal charge?
Oxidation number assumes all shared electrons belong to the more electronegative atom (as if bonds were completely ionic). Formal charge assumes electrons in a bond are shared equally between both atoms. Oxidation numbers are used for redox chemistry and nomenclature, while formal charges are used to evaluate the best Lewis structure. For CO2, carbon has oxidation state +4 but formal charge 0. Both concepts are useful but serve different purposes in chemistry.
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Can I use the results for professional or academic purposes?
You may use the results for reference and educational purposes. For professional reports, academic papers, or critical decisions, we recommend verifying outputs against peer-reviewed sources or consulting a qualified expert in the relevant field.