The oxidation state reference provides typical oxidation numbers for common elements, searchable by element symbol or name. Includes the rules for assigning oxidation states and compound examples for each element.
Search Oxidation States
Oxidation State Rules
Common Elements Reference
| Symbol | Element | Common States | Example Compound |
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How to Use the Oxidation State Reference
Oxidation states are a bookkeeping tool for electrons in chemical reactions. They help balance redox equations and determine what's being oxidized and reduced. This reference provides common oxidation states and rules for assigning them.
How to Find an Element's Oxidation State
Type the element symbol (e.g., "Fe") or name (e.g., "iron") in the search box. The result shows all common oxidation states with compound examples. Iron, for instance, commonly exists as Fe²⁺ (in FeO, FeCl₂) and Fe³⁺ (in Fe₂O₃, FeCl₃).
The Priority Rules
When assigning oxidation states in a compound: (1) Pure element = 0, (2) Monoatomic ion = charge, (3) F is always −1, (4) O is usually −2 (except H₂O₂ = −1), (5) H is +1 with nonmetals, −1 with metals, (6) Sum = 0 for neutral compound or = charge for ion.
Worked Example: Cr₂O₇²⁻
The dichromate ion has charge −2. Oxygen = −2, so 7 oxygens = −14. The two Cr atoms must sum to +12 to give net −2. Therefore each Cr = +6. This is Cr(VI), a strong oxidizer. Apply the same method to any compound: set up the equation and solve for the unknown element's oxidation state.
FAQ
What is an oxidation state?
An oxidation state (or oxidation number) is a hypothetical charge an atom would have if all bonds were ionic. It helps track electron transfer in redox reactions. Oxidation states are not actual charges but a bookkeeping convention for balancing redox equations.
What are the basic rules for assigning oxidation states?
Key rules: (1) Pure element = 0, (2) Monoatomic ion = its charge, (3) Oxygen = -2 (except in peroxides: -1), (4) Hydrogen = +1 (except metal hydrides: -1), (5) Fluorine = -1 always, (6) Sum of all oxidation states in a neutral compound = 0.
What is the oxidation state of iron in Fe₂O₃?
Oxygen is -2 (3 oxygens = -6 total). The compound is neutral, so two Fe atoms must sum to +6. Therefore each Fe = +3. Iron(III) oxide (rust) contains Fe³⁺.
Is this reference free?
Yes, completely free with no signup required. All lookups run in your browser.
What is the difference between oxidation and reduction?
Oxidation is loss of electrons (oxidation state increases). Reduction is gain of electrons (oxidation state decreases). They always occur together — memory aid: OIL RIG (Oxidation Is Loss, Reduction Is Gain). The oxidizing agent gets reduced; the reducing agent gets oxidized.