Hydrogen Oxidation States
Quick reference for the three oxidation states of hydrogen (+1, −1, and 0) with real compound examples and the bonding rules that determine each state.
Bonded to a more electronegative nonmetal
Hydrogen donates electron density to the more electronegative partner (O, N, Cl, F, S). It behaves as an electrophile or proton donor (Brønsted acid).
Bonded to a less electronegative metal
Hydrogen gains electron density from an electropositive metal and acts as the hydride ion (H⁻). These compounds are strong reducing agents.
Pure element or symmetric H–H bond
In diatomic H₂ both atoms are identical; electrons are shared equally so neither carries net charge. This is the reference state for standard enthalpies.
Rules for Assigning Hydrogen's Oxidation State
The oxidation state of any pure element is defined as zero. For hydrogen this means H₂ gas, atomic H•, and any symmetrical H–H fragment.
When hydrogen bonds to a more electronegative nonmetal (F, O, N, Cl, Br, I, S, C), it carries an oxidation state of +1. This covers water, all common acids, and nearly all organic C–H bonds.
When hydrogen bonds to Group 1 (alkali metals) or Group 2 (alkaline earth metals), or certain other electropositive metals, it is more electronegative and takes oxidation state −1 as the hydride ion H⁻.
In complex reducing agents such as LiAlH₄ (lithium aluminum hydride) or NaBH₄ (sodium borohydride), hydrogen is still −1 because it is bonded to electropositive metal centers (Al or B acting as electron-deficient Lewis acids).
After applying the rules above, verify that the sum of all oxidation states equals the overall charge of the species (0 for neutral molecules, −1 for anions like H⁻, etc.).
Compound Examples by Oxidation State
| Compound | Formula | H Oxidation State | Class | Notes |
|---|---|---|---|---|
| Water | H₂O | +1 | Oxide | +1 verified: O is −2, 2×(+1)+(−2)=0 |
| Hydrochloric acid | HCl | +1 | Halide acid | Cl is −1; H is +1 |
| Sulfuric acid | H₂SO₄ | +1 | Oxyacid | S is +6, O is −2; H is +1 |
| Nitric acid | HNO₃ | +1 | Oxyacid | N is +5, O is −2; H is +1 |
| Ammonia | NH₃ | +1 | Molecular | N is −3; 3×(+1)+(−3)=0 |
| Methane | CH₄ | +1 | Organic | C is −4; 4×(+1)+(−4)=0 |
| Hydrogen peroxide | H₂O₂ | +1 | Peroxide | O is −1; H remains +1 |
| Phosphoric acid | H₃PO₄ | +1 | Oxyacid | P is +5, O is −2; H is +1 |
| Sodium hydride | NaH | −1 | Ionic hydride | Na is +1; H is −1 (H⁻) |
| Calcium hydride | CaH₂ | −1 | Ionic hydride | Ca is +2; 2×(−1)+(+2)=0 |
| Lithium hydride | LiH | −1 | Ionic hydride | Li is +1; H is −1 |
| Lithium aluminum hydride | LiAlH₄ | −1 | Complex hydride | Al is +3; all 4 H are −1 |
| Sodium borohydride | NaBH₄ | −1 | Complex hydride | B is +3; all 4 H are −1 |
| Magnesium hydride | MgH₂ | −1 | Ionic hydride | Mg is +2; H is −1 |
| Hydrogen gas | H₂ | 0 | Elemental | Symmetric bond; no net charge |
| Atomic hydrogen | H• | 0 | Elemental | Free radical; pure element state |
Quick Oxidation State Lookup
Type a compound name or formula to find hydrogen's oxidation state in our reference list.
Start typing to filter compounds.
Decision Guide: Which State Applies?
Is hydrogen alone or in H₂?
If the compound is pure H₂ gas or atomic hydrogen H•, the oxidation state is 0 by definition. No further analysis needed.
Is hydrogen bonded to a metal?
If bonded to an alkali metal (Li, Na, K, Rb, Cs), alkaline earth metal (Mg, Ca, Ba), or another electropositive metal, hydrogen is −1 (hydride ion).
Is hydrogen bonded to a nonmetal?
If bonded to O, N, C, S, F, Cl, Br, or another nonmetal more electronegative than hydrogen, the oxidation state is +1. This is the default for the vast majority of compounds.
Hydrogen as a Reducing Agent
When H₂ (oxidation state 0) reacts and becomes H⁺ (+1), hydrogen is oxidized — it loses electron density. H₂ therefore acts as a reducing agent in these reactions.
(oxidation: 0 → +1)
Examples: combustion of H₂, fuel cell reactions, reduction of metal oxides.
Hydrogen as an Oxidizing Agent
When H₂ (oxidation state 0) reacts and becomes H⁻ (−1), hydrogen is reduced — it gains electron density. H₂ therefore acts as an oxidizing agent in these reactions.
(reduction: 0 → −1)
Examples: synthesis of NaH, CaH₂, LiH from metals and H₂ gas.
Summary
Quick reference for the three oxidation states of hydrogen (+1, −1, and 0) with real compound examples and the bonding rules that determine each state.
How it works
- Review the three possible oxidation states: +1, −1, and 0.
- Check the bonding rule: hydrogen is +1 when bonded to a more electronegative nonmetal.
- Check the hydride rule: hydrogen is −1 when bonded to a less electronegative metal (Groups 1 and 2).
- Check the elemental rule: hydrogen is 0 in H₂ or in any symmetrical H–H bond.
- Browse the compound examples table to identify which state applies to a given molecule.
- Use the exceptions panel to handle edge cases like NaH, LiAlH₄, and interstitial hydrides.
Use cases
- Assign oxidation numbers in redox reaction equations.
- Determine whether hydrogen acts as an oxidizing or reducing agent.
- Identify metal hydrides versus protic acids in inorganic chemistry.
- Balance half-reactions in electrochemistry involving hydrogen.
- Teach or review oxidation state rules in introductory chemistry courses.
- Verify oxidation state assignments in organic and biochemical mechanisms.
- Classify hydrogen compounds for solubility and reactivity predictions.
- Support AP Chemistry, IB Chemistry, or university-level exam preparation.