What oxidation states can polonium have?

Polonium most commonly exhibits +2 and +4. The +4 state is the most stable and widespread, appearing in polonium dioxide (PoO2), polonium tetrachloride (PoCl4), and related tetrahalides. The +2 state appears in polonium(II) oxide (PoO) and polonium(II) chloride (PoCl2). Less common states include -2 (in polonides such as Na2Po), 0 (elemental), and +6 (in PoO3, though this is quite unstable).

Why does polonium prefer +4 over +6?

The inert-pair effect is very pronounced for polonium: the 6s2 electron pair is stabilized by relativistic contraction and the high nuclear charge, making it harder to oxidize than the equivalent pair in sulfur or selenium. Sulfur and selenium reach +6 readily (H2SO4, H2SeO4), but polonium's +6 state (PoO3) is so unstable that the compound readily loses oxygen to give +4. The +4 state — where only the 6p electrons are involved — is far more accessible.

How do I find the oxidation state of Po in PoO2?

Assign oxygen first: O = -2. Two O atoms total -4. The compound is neutral: Po + 2(-2) = 0 → Po + (-4) = 0 → Po = +4.

What is the oxidation state of polonium in PoCl2?

Chlorine is -1. Two Cl atoms total -2. The molecule is neutral: Po + 2(-1) = 0 → Po = +2.

Is polonium radioactive and does that affect its chemistry?

Yes, all polonium isotopes are radioactive. The most studied is 210Po, which decays by alpha emission with a half-life of 138 days. Intense radioactivity means bulk polonium chemistry is carried out in heavily shielded facilities. In very dilute solution, radiation damage to the solvent (radiolysis) can alter apparent speciation. Chemically, polonium still follows its Group 16 valence shell rules, but radiation self-heating is significant at macro scale.

Polonides are ionic compounds where polonium carries a formal -2 oxidation state (Po2-), analogous to sulfides (S2-), selenides (Se2-), and tellurides (Te2-). Examples include Na2Po (sodium polonide) and K2Po (potassium polonide). They form when polonium reacts with active metals and are extremely hazardous because they combine chemical toxicity with intense radioactivity.

Polonium Oxidation States

Reference for all common polonium oxidation states (+2 and +4) with example compounds, identification tips, and a compound-to-oxidation-state lookup.

Atomic # 84 Po Polonium

Atomic Mass

209 u (most stable)

Group

16 (VIA)

Period

Block

p-block

Electronegativity

2.0 (Pauling)

Oxidation States

-2, 0, +2, +4, +6

Polonium has five known oxidation states. The +4 state is the most common. Click a state card to see its compounds and how to identify it.

Oxidation State −2

In the -2 oxidation state, polonium (Po^2-) behaves as a heavy chalcogenide anion, analogous to sulfide (S^2-), selenide (Se^2-), and telluride (Te^2-). This state forms when polonium reacts with highly electropositive metals that donate electrons to the partially filled 6p shell of polonium, completing it. Because all polonium isotopes are radioactive, these polonide salts are among the most hazardous chemical substances known — combining radiological and chemical danger.

How to Identify This State

In a binary polonide MₙPo: assign the metal its standard cation charge, then solve for Po. For Na₂Po: 2(+1) + Po = 0 → Po = -2. For K₂Po: 2(+1) + Po = 0 → Po = -2. Any compound where Po bonds exclusively to a less electronegative metal will yield a negative oxidation state.

Example Compounds

Formula	Name	Assignment	Notes
Na₂Po	Sodium Polonide	2(+1) + Po = 0 → Po = -2	Ionic polonide; reacts with water to release H₂Po (polonium hydride). Intensely radioactive.
K₂Po	Potassium Polonide	2(+1) + Po = 0 → Po = -2	Formed by direct reaction of potassium metal with polonium. Extremely hazardous.
H₂Po	Polonium Hydride	2(+1) + Po = 0 → Po = -2	Gaseous compound analogous to H₂S and H₂Te; extremely unstable and radioactive.

Common Uses

Fundamental research on heavy chalcogenide chemistry
Comparison studies of Group 16 anion stability trends
Radiotracer studies (academic research only)
Not used in any commercial application due to extreme radioactivity and toxicity

Oxidation State 0

Elemental polonium is assigned an oxidation state of zero by convention. Polonium is unique among all elements in crystallizing in a simple cubic lattice (alpha-Po at room temperature), making it the only element with this structure. It is a silvery-gray metalloid that looks much like tellurium. At around 36 °C a phase transition occurs to a rhombohedral beta-Po form. Elemental polonium is produced in milligram quantities by neutron irradiation of bismuth-209 in nuclear reactors.

How to Identify This State

Any pure elemental polonium — the alpha or beta allotrope — carries oxidation state 0 by definition. No arithmetic required.

Example Compounds

Formula	Name	Assignment	Notes
Po (alpha)	Alpha-Polonium	Elemental → Po = 0	Simple cubic crystal structure; stable below ~36 °C. Only element with this lattice type. Silvery-gray metalloid.
Po (beta)	Beta-Polonium	Elemental → Po = 0	Rhombohedral structure; stable above ~36 °C. Transitions reversibly from alpha on heating.

Common Uses

Alpha-particle source in static eliminators (anti-static devices)
Nuclear physics research and neutron sources (Po + Be)
Thermoelectric power sources for space applications (historical)
Initiation trigger in early nuclear weapons (historical, Po-Be sources)

Oxidation State +2

The +2 state arises when polonium loses or formally donates its two 6p electrons while the 6s² inert pair remains intact. The strong inert-pair effect — amplified by relativistic stabilization of the 6s electrons — makes the +2 state more accessible for polonium than for any other Group 16 element above it. Polonium(II) compounds are strong oxidizing agents. PoO is a gray, amphoteric solid; PoCl₂ is a yellow-orange solid that disproportionates on heating.

How to Identify This State

In PoCl₂: Cl = -1, two atoms total -2, molecule neutral → Po + 2(-1) = 0 → Po = +2. In PoO: O = -2, formula neutral → Po + (-2) = 0 → Po = +2. The pattern: one polonium atom balances two singly-charged anions or one doubly-charged anion.

Example Compounds

Formula	Name	Assignment	Notes
PoO	Polonium(II) Oxide	Po + 1(-2) = 0 → Po = +2	Gray, amphoteric solid. Less stable than PoO₂ (+4). Dissolves in both acid and base.
PoCl₂	Polonium(II) Chloride	Po + 2(-1) = 0 → Po = +2	Yellow-orange solid. Disproportionates on heating to give PoCl₄ and elemental Po.
PoBr₂	Polonium(II) Bromide	Po + 2(-1) = 0 → Po = +2	Black solid; less stable than PoBr₄. Formed at lower temperatures.
Po²⁺	Polonium(II) ion	Ion charge = +2 → Po = +2	Exists in strongly acidic aqueous solutions. Readily oxidized to Po⁴⁺ in air.

Common Uses

Radiochemistry research on heavy chalcogen cation behavior
Fundamental studies of inert-pair effect in Period 6 elements
Not commercially produced or used due to radioactivity
Comparison with tellurium(II) chemistry in academic research

Oxidation State +4

The +4 state is the most stable and most chemically accessible oxidation state of polonium. It involves loss of the two 6p electrons plus formal engagement of two 6s electrons (or viewed alternatively, the 6s² pair participates in bonding). PoO₂ is the main oxide and forms a fluorite-like structure. The tetrahalides PoCl₄, PoBr₄, and PoI₄ are all known. In solution, Po(IV) forms the PoO₂²⁺ ion in acidic conditions and hydrolyzes at higher pH.

How to Identify This State

In PoO₂: O = -2, two O atoms total -4, neutral → Po + 2(-2) = 0 → Po = +4. In PoCl₄: Cl = -1, four Cl atoms total -4 → Po + 4(-1) = 0 → Po = +4. Pattern: one Po balancing four singly-charged anions or two doubly-charged anions.

Example Compounds

Formula	Name	Assignment	Notes
PoO₂	Polonium(IV) Dioxide	2(-2) + Po = 0 → Po = +4	Most important polonium compound. Yellow solid with fluorite-like structure. Amphoteric oxide.
PoCl₄	Polonium(IV) Chloride	4(-1) + Po = 0 → Po = +4	Yellow solid; hydrolyzes readily with water. Melts at 300 °C.
PoBr₄	Polonium(IV) Bromide	4(-1) + Po = 0 → Po = +4	Dark red-brown solid. More thermally stable than PoBr₂.
[PoCl₆]^2-	Hexachloropolonate(IV)	6(-1) + Po = -2 → Po = +4	Octahedral complex formed in concentrated HCl; one of the best-characterized polonium species.

Common Uses

Most stable form for radiochemistry experiments
Alpha-source production (PoO₂ targets)
Neutron source when mixed with beryllium
Reference compound for polonium speciation in environmental and biomedical research

Oxidation State +6

The +6 oxidation state is the highest known for polonium and is extremely rare and unstable. It would require full ionization of the 6s² pair — exactly what the inert-pair effect resists. PoO₃ has been reported but is a powerful oxidant that reverts to PoO₂ readily. By contrast, the Group 16 neighbors SO₃, SeO₃, and TeO₃ are all stable, illustrating how dramatically the inert-pair effect increases at Period 6.

How to Identify This State

In PoO₃: O = -2, three O atoms total -6, neutral → Po + 3(-2) = 0 → Po + (-6) = 0 → Po = +6. The high charge and the scarcity of +6 polonium compounds distinguish this state from +4.

Example Compounds

Formula	Name	Assignment	Notes
PoO₃	Polonium(VI) Trioxide	3(-2) + Po = 0 → Po = +6	Reported but highly unstable; reverts to PoO₂ + O₂. Strong oxidizer.
PoO₄^2-	Polonate(VI) Ion	4(-2) + Po = -2 → Po = +6	Hypothetical species analogous to selenate and tellurate; not well characterized.

Common Uses

Academic research only — illustrates the limits of inert-pair effect
Comparison studies of Group 16 maximum oxidation states
No practical or commercial use; compound is too unstable

Oxidation State Summary

State	Stability	Key Example	Notes
-2	Rare	Na₂Po	Polonide anion; forms with highly electropositive metals; extremely hazardous.
0	Elemental	Po (alpha)	Only element with simple cubic crystal structure; produced via neutron irradiation of Bi-209.
+2	Less Common	PoCl₂	Strong inert-pair effect leaves 6s² pair intact; +2 state less stable than +4.
+4	Most Stable	PoO₂	Most common and stable state; fluorite-like PoO₂ is the principal compound.
+6	Very Rare	PoO₃	Extremely unstable; inert-pair effect prevents stabilization of fully oxidized state.

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Summary

Polonium (Po, atomic number 84) is a radioactive metalloid in Group 16 that primarily exhibits +2 and +4 oxidation states, with +4 being the most common. Its ground-state electron configuration is [Xe] 4f14 5d10 6s2 6p4. The element sits below tellurium in Group 16 and shows pronounced inert-pair effect: the 6s2 electrons are stabilized by relativistic contraction, making the +2 state (where only the 6p electrons are lost) more accessible than for lighter group members. Polonium is the only element known to adopt a simple cubic crystal structure and is intensely radioactive, decaying primarily by alpha emission.

How it works

Click an oxidation state card (+2, +4, or other) to open its detail panel.
The detail panel shows a description, example compounds, step-by-step assignment, and identification tips.
Use the Compound Lookup tab to select a known polonium compound and see the oxidation state of Po explained step by step.
Click any formula badge to copy it to your clipboard.
Switch between the Explorer and Compound Lookup tabs using the tab bar.

Use cases

Students studying Group 16 oxidation state trends for advanced chemistry exams.
Chemistry teachers preparing reference materials on heavy p-block elements and the inert-pair effect.
Researchers checking the oxidation state of polonium in a specific compound or reaction.
Nuclear chemists and radiochemists working with polonium isotopes and their compounds.
Learners comparing oxidation-state trends down Group 16 (O, S, Se, Te, Po).

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu

Polonium Oxidation States

Use the Polonium Oxidation States

Example Compounds

Common Uses

Example Compounds

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Example Compounds

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Example Compounds

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Example Compounds

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Oxidation State Summary

Summary

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Frequently Asked Questions