Reference for all common polonium oxidation states (+2 and +4) with example compounds, identification tips, and a compound-to-oxidation-state lookup.
Atomic #84PoPolonium
Atomic Mass
209 u (most stable)
Group
16 (VIA)
Period
6
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 (Po2-) behaves as a heavy chalcogenide anion, analogous to sulfide (S2-), selenide (Se2-), and telluride (Te2-). 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.
PoO42-
Polonite(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
Select a compound from the list to see the oxidation state of polonium
with a step-by-step calculation.
Select a compound to see the oxidation state calculation.
Oxidation state of Po:
Step-by-step
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.
Copied!
Summary
Reference for all common polonium oxidation states (+2 and +4) with example compounds, identification tips, and a compound-to-oxidation-state lookup.
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
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).
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.
Assign oxygen first: O = -2. Two O atoms total -4. The compound is neutral: Po + 2(-2) = 0 → Po + (-4) = 0 → Po = +4.
Chlorine is -1. Two Cl atoms total -2. The molecule is neutral: Po + 2(-1) = 0 → Po = +2.
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.
