Plutonium Oxidation States
Reference for all known oxidation states of Plutonium (Pu, element 94) — +3 through +7 plus the elemental metal (0) — with compounds, stability notes, and an interactive state selector.
Plutonium (Pu) is a dense, silvery-gray actinide metal with an electron configuration of [Rn] 5f⁶ 7s². It is one of the most chemically complex elements known, capable of existing in six oxidation states (0 through +7, with +7 rare) and — uniquely — all four ionic states (+3, +4, +5, +6) can coexist in the same aqueous solution. PuO₂ (+4) is the most thermodynamically stable solid compound and the standard form for fuel and storage.
Interactive State Explorer
Select an oxidation state above.
All Oxidation States
| State | Ion / Form | Stability | Notes |
|---|---|---|---|
| 0 | Pu(s) | Elemental metal | Dense silvery metal; six allotropic forms; reacts with air and water |
| +3 | Pu³⁺ | Stable (reducing) | Blue-violet in solution; common under reducing conditions; PuF₃, PuCl₃ |
| +4 | Pu⁴⁺ | Most stable solid | Tan/brown in solution; PuO₂ is the standard storage form; dominates solid-state chemistry |
| +5 | PuO₂⁺ | Least stable ionic | Pink/rose in solution; dioxo cation; disproportionates readily to +4 and +6 |
| +6 | PuO₂²⁺ | Stable (oxidizing) | Orange-yellow in solution; linear dioxo cation; forms under oxidizing conditions |
| +7 | PuO₅³⁻ (aq) | Rare | Confirmed only in strongly alkaline, strongly oxidizing solutions; not observed in normal chemistry |
Why So Many Oxidation States?
Plutonium's configuration is [Rn] 5f⁶ 7s². Unlike the 4f electrons in lanthanides, the 5f electrons in early actinides sit close in energy to 6d and 7s electrons and are chemically active. This allows Pu to donate varying numbers of electrons across a wide redox window.
For plutonium, the 5f, 6d, and 7s subshells have similar energies. Small changes in ligand field, pH, or redox potential can shift the system between states. This is why the chemistry is so sensitive to experimental conditions.
In the +5 and +6 states, Pu forms linear PuO₂⁺ and PuO₂²⁺ ions, where two oxygen atoms bond covalently to the central Pu. This structural adaptation stabilizes the high oxidation states in aqueous solution — a pattern shared with U and Np but absent in lighter transition metals.
Key Compounds by State
Purple solid; LaF₃-type structure; one of the more accessible +3 compounds under reducing conditions.
Black/olive ceramic; fluorite structure; most stable bulk form of Pu; used in MOX fuel and RTGs.
Emerald-green solid; forms in reducing HCl solutions; UCl₃-type structure.
Tan solid; isolable from sulfuric acid solution; illustrates +4 in non-oxide solid-state form.
Pink/rose in acidic solution; least stable common aqueous state; disproportionates to +4 and +6.
Orange-yellow in solution; forms under strongly oxidizing conditions; analogous to UO₂²⁺ (uranyl).
PuO₂ is the dominant solid form encountered in nuclear industry and research. Solution speciation depends strongly on pH and redox potential.
Coexistence of Multiple States in Solution
Plutonium is the only element confirmed to exhibit all four ionic oxidation states simultaneously in a single aqueous solution. In mildly acidic perchlorate solution (~1 M HClO₄), the following disproportionation equilibria operate concurrently:
The result is a mixture containing measurable concentrations of Pu³⁺, Pu⁴⁺, PuO₂⁺, and PuO₂²⁺ at equilibrium. This behavior is a direct consequence of the nearly equal standard reduction potentials between consecutive plutonium couples, which lie close together near 1 V vs. NHE. Temperature, acid concentration, and total Pu concentration all shift the equilibrium distribution.
Comparison to Neighboring Actinides
| Element | Z | Common states | Most stable solid |
|---|---|---|---|
| Uranium (U) | 92 | +3, +4, +5, +6 | UO₂ (+4) |
| Neptunium (Np) | 93 | +3, +4, +5, +6, +7 | NpO₂ (+4) |
| Plutonium (Pu) | 94 | 0, +3, +4, +5, +6, +7 | PuO₂ (+4) |
| Americium (Am) | 95 | +2, +3, +4, +5, +6 | AmO₂ (+4) |
Plutonium sits at the crossover where 5f electrons are most evenly balanced between localized and itinerant behavior — partly why it has the most accessible redox states of the series.
Summary
Reference for all known oxidation states of Plutonium (Pu, element 94) — +3 through +7 plus the elemental metal (0) — with compounds, stability notes, and an interactive state selector.
How it works
- Select an oxidation state using the interactive tabs to see its description, common compounds, and stability notes.
- Review the full oxidation states table for a side-by-side comparison of all states and their relative stability.
- Read the electron configuration section to understand why 5f electron participation enables so many states.
- Check the disproportionation note to understand the unusual coexistence of multiple Pu states in solution.
Use cases
- Looking up the oxidation state of plutonium for a nuclear chemistry or radiochemistry problem.
- Understanding why PuO₂ is the preferred storage form and the most stable solid-state compound.
- Writing balanced redox equations involving Pu³⁺, Pu⁴⁺, PuO₂⁺, or PuO₂²⁺ species.
- Studying how multiple oxidation states of plutonium can coexist in aqueous solution simultaneously.
- Comparing plutonium oxidation chemistry to neighboring actinides uranium and neptunium.