Why does radium only have a +2 oxidation state?

Radium has the electron configuration [Rn] 7s2. Removing both 7s electrons achieves the stable radon noble-gas configuration. The lattice and hydration energies of Ra2+ compounds far exceed the first two ionization energies, driving all stable chemistry to +2. A third ionization would breach the stable [Rn] core at prohibitive energy cost.

Does radium ever show a +1 oxidation state?

No stable +1 radium compound is known. A transient +1 state may be detectable in gas-phase experiments at extreme temperatures, but it instantly disproportionates to Ra(0) and Ra2+. Under any ordinary conditions radium is exclusively +2.

What is radium's electron configuration?

Ground state: [Rn] 7s2. When ionized to Ra2+, both 7s electrons are removed, leaving the radon noble-gas core: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 4f14 5s2 5p6 5d10 6s2 6p6.

Why is radium more reactive than barium?

Descending Group 2, each successive element has its outermost electrons further from the nucleus and more shielded by inner shells. Radium's 7s electrons have the lowest ionization energies in Group 2, making Ra the most electropositive alkaline earth metal and the most chemically reactive — though its extreme radioactivity is the dominant practical concern.

What are the most notable radium compounds?

Radium chloride (RaCl2), radium bromide (RaBr2), radium sulfate (RaSO4), and radium carbonate (RaCO3) are the most studied. All feature Ra2+. RaSO4 is extremely insoluble. Historically RaBr2 was isolated by Marie Curie in her pioneering separation work.

Is radium used in medicine today?

Radium-223 dichloride (Xofigo) is an FDA-approved alpha-emitting radiopharmaceutical used to treat bone metastases in prostate cancer. It targets bone tissue because Ra2+ mimics Ca2+ and Sr2+, incorporating into hydroxyapatite. Earlier radium dial paint and radium water uses have been abandoned due to radiation hazard.

Radium Oxidation States

Reference for radium oxidation states: Ra is exclusively +2 in all compounds, with electron configuration, ionization energies, radioactivity notes, and key compounds explained.

Atomic # 88 Ra Radium

Atomic Mass

226 u (most stable)

Group

2 (IIA)

Period

Block

s-block

Electronegativity

0.89 (Pauling)

Oxidation States

+2 (only stable)

Radioactive element. All radium isotopes are radioactive. The most stable is ²²⁶Ra (half-life 1,600 years, alpha emitter). Radium chemistry is studied in trace quantities under strict radiation safety conditions.

Radium exhibits one oxidation state in all stable compounds: +2. Its ground-state configuration is [Rn] 7s² — losing both valence electrons reaches the stable radon noble-gas core. The energy recovered from Ra²⁺ compound formation (lattice and hydration energies) exceeds the two ionization costs, and a third ionization would require breaching the [Rn] core — energetically inaccessible. Radium is the heaviest naturally occurring alkaline earth metal and the most electropositive element in Group 2.

Oxidation State	Stability	Notes
+2	Stable	Universal state in all ordinary compounds. Ra loses both 7s² electrons to achieve the [Rn] configuration. High lattice and hydration energies drive this thermodynamically.
0	Elemental only	Assigned to pure radium metal by convention. Not a compound oxidation state. Radium metal is a brilliant white solid that rapidly blackens due to nitride formation and self-irradiation.
+1	Not isolable	No stable +1 compound known. Any transient Ra⁺ in gas-phase conditions disproportionates instantly to Ra(0) + Ra²⁺. Not accessible under ordinary conditions.

Ionization Energies
IE₁ = 509.3 kJ/mol | IE₂ = 979.0 kJ/mol | IE₃ ≈ 3300 kJ/mol (est.)
The large jump from IE₂ to IE₃ confirms why +2 is the ceiling — the third ionization would breach the stable [Rn] noble-gas core, costing far more energy than any compound formation can recover.

All known radium compounds feature Ra in the +2 oxidation state. Because Ra²⁺ closely resembles Ba²⁺ and Ca²⁺ in size and charge, radium chemistry closely parallels barium chemistry. Radium salts tend to be ionic, and most radium compounds are studied only in trace quantities due to extreme radioactive hazard.

Compound	Formula	Ra State	Notes
Radium Chloride	RaCl₂	+2	Crystalline white solid; first pure radium compound isolated by Marie and Pierre Curie in 1898. Soluble in water. Historically separated from uranium ore by differential precipitation. Extremely radioactive.
Radium Bromide	RaBr₂	+2	Similar to RaCl₂; used by Marie Curie in her early isolation and characterization work. White solid, water-soluble. Used in historical spectroscopic identification of radium.
Radium Sulfate	RaSO₄	+2	Extremely insoluble white solid (Ksp ≈ 4×10⁻¹¹), isostructural with BaSO₄. Occurs naturally in uranium ores as a decay product of ²³⁸U. Precipitates readily from solution.
Radium Carbonate	RaCO₃	+2	Insoluble white solid; used historically to convert between other radium salts. Decomposes on heating to RaO and CO₂.
Radium Oxide	RaO	+2	Basic oxide; reacts with water to form Ra(OH)₂. Analogous to BaO. Formed when radium metal oxidizes in air.
Radium Hydroxide	Ra(OH)₂	+2	Strong base; the most soluble of the Group 2 hydroxides descending from Be to Ra. Analogous to Ba(OH)₂.
Radium Nitrate	Ra(NO₃)₂	+2	Soluble oxidizer; analogous to Ba(NO₃)₂. Used in historical separation procedures alongside barium nitrate.
Radium-223 Dichloride	²²³RaCl₂	+2	Radiopharmaceutical (trade name Xofigo); FDA-approved for treatment of bone metastases in castration-resistant prostate cancer. Targets bone via Ra²⁺ mimicking Ca²⁺ in hydroxyapatite.

Ground State Configuration

Core

Core (completes [Rn])

Valence — both lost on ionization to Ra²⁺

Notation

Noble gas: [Rn] 7s²

Ra²⁺ ion: [Rn] = [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁶

Ionization Steps

[Rn] 7s²

Neutral atom — 2 valence electrons

Ra⁺

[Rn] 7s¹

Remove first 7s electron (IE₁ 509.3 kJ/mol)

Ra²⁺

[Rn]

Remove second 7s electron (IE₂ 979.0 kJ/mol) — stable, noble-gas core

Ra³⁺

Break [Rn] core

Would require IE₃ ~3300 kJ/mol (est.) — not accessible under ordinary conditions

Why the large jump at IE₃? Removing both 7s electrons clears the outer valence shell, reaching the stable [Rn] radon core. The third ionization would pull an electron from the 6p shell within that noble-gas core, requiring roughly 3300 kJ/mol versus 979 kJ/mol for IE₂. This discontinuity explains why +2 is the absolute ceiling for radium under ordinary conditions.

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Summary

Radium (Ra) is a radioactive alkaline earth metal with atomic number 88. It exhibits a single stable oxidation state of +2 in all known compounds, formed by losing both 7s valence electrons to reach the stable radon ([Rn]) noble-gas core. This reference covers its electron configuration, ionization energy data, the chemistry of key radium compounds, and why its radioactivity — not its oxidation chemistry — limits practical applications.

How it works

Click a tab — Oxidation States, Compounds, Electron Config, or Physical Props — to explore each area.
The Oxidation States panel explains why +2 is the only stable state, with a table and ionization energy data.
The Compounds panel lists known radium compounds with their formulas, Ra state assignment, and notes on radioactive hazard.
The Electron Config panel shows orbital filling and the ionization steps from Ra to Ra2+.
The Physical Props panel provides atomic and material data for quick reference.
Click any monospace table cell to copy its value to your clipboard.

Use cases

Students studying Group 2 trends and the chemistry of heavy alkaline earth metals.
Chemistry teachers preparing lessons on radioactive elements and oxidation states.
Nuclear chemistry researchers needing a quick reference for radium chemistry.
Anyone studying the periodic table trends from calcium through radium in Group 2.
Students preparing for chemistry exams covering Period 7 or Group 2 elements.

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