What oxidation states does strontium have?

Strontium has two oxidation states in practice: 0 (elemental strontium) and +2 (in all its compounds). The +2 state arises from complete loss of the two 5s electrons. No stable +1 compounds of strontium are known under standard conditions.

Why does strontium only form +2 compounds?

Strontium is a Group 2 (alkaline earth) metal with the configuration [Kr] 5s². Both valence electrons are removed during typical ionic bond formation. The second ionization energy (1064 kJ/mol) is accessible, and the high lattice energies of Sr²⁺ compounds far outweigh any energy penalty. There is no partially filled d sub-shell to enable other valence states, so +2 is the only chemically stable option.

What is the oxidation state of Sr in SrO?

Oxygen is -2. The compound is neutral: Sr + (-2) = 0, so Sr = +2.

What is the oxidation state of Sr in SrCl₂?

Each Cl is -1. Two Cl atoms total -2. The compound is neutral: Sr + 2(-1) = 0, so Sr = +2.

What is strontium-90 and what oxidation state does it have?

Strontium-90 (⁹⁰Sr) is a radioactive isotope produced by nuclear fission. Chemically it behaves identically to stable strontium and exists in the +2 oxidation state. It is a health concern because the body mistakes Sr²⁺ for Ca²⁺ and deposits it in bone tissue, where it irradiates bone marrow.

What is the oxidation state of Sr in SrTiO₃?

In strontium titanate (SrTiO₃), strontium is +2 (as always). Oxygen is -2 (three atoms: -6 total). The formula unit is neutral: Sr + Ti + 3O = 0 → (+2) + Ti + (-6) = 0 → Ti = +4. So Sr = +2 and Ti = +4.

Strontium Oxidation States

Name: Strontium Oxidation States
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Author: Nham Vu

Reference for all strontium oxidation states (0 and +2) with example compounds, step-by-step assignments, and a compound lookup.

Atomic # 38 Sr Strontium

Atomic Mass

87.62 u

Group

2 (IIA)

Period

Block

s-block

Electronegativity

0.95 (Pauling)

Oxidation States

0, +2

Strontium has two oxidation states. Click a state card to see its compounds, uses, and how to identify it.

Oxidation State 0

Elemental strontium is assigned an oxidation state of zero by convention — all pure elements are defined as zero regardless of allotrope. Strontium metal is a soft, silvery-white solid that tarnishes rapidly in air, forming a yellow oxide coat. It is reactive enough to burn in air with a characteristic bright crimson flame, the same emission responsible for red colors in fireworks and flares.

How to Identify This State

Any specimen of pure strontium metal carries oxidation state 0 by definition. No arithmetic is needed — elemental substances are always zero.

Example Compounds

Formula	Name	Assignment	Notes
Sr (metal)	Strontium Metal	Elemental → Sr = 0	Soft, silvery-white alkaline earth metal. Reacts vigorously with water and burns in air. Stored under mineral oil to prevent oxidation.
Sr (vapor)	Strontium Vapor	Elemental → Sr = 0	Produced at high temperatures; important in the flame test. The 5s→5p transition emits the characteristic red/crimson color at 460 nm.

Common Uses

Red coloring agent in fireworks and emergency flares (via combustion to Sr²⁺ emitters)
Getter material in vacuum tubes to remove residual gas molecules
Research into strontium Bose-Einstein condensates (ultra-cold atom physics)
Standard reference material in spectroscopy and flame tests

Oxidation State +2

The +2 state is the only stable oxidation state of strontium in compounds. It results from the complete loss of the two 5s valence electrons ([Kr] 5s² → [Kr] + 2e⁻), yielding the Sr²⁺ cation with the noble-gas krypton core. Sr²⁺ has an ionic radius of 118 pm, slightly larger than Ca²⁺ (100 pm) but smaller than Ba²⁺ (135 pm). This size governs solubility trends: strontium sulfate (SrSO₄) is sparingly soluble like BaSO₄, while strontium chloride is freely soluble like CaCl₂.

How to Identify This State

In any Sr compound, assign known oxidation states first, set the expression equal to the overall charge, and solve for Sr. Because strontium is always +2, you can also go in reverse: knowing Sr = +2, verify the other elements balance. Example — SrSO₄: SO₄ carries -2, Sr is +2, total = 0. ✓

Example Compounds

Formula	Name	Assignment	Notes
SrO	Strontium Oxide	O = -2; neutral: Sr + (-2) = 0 → Sr = +2	White solid formed by combustion of Sr in air or thermal decomposition of SrCO₃. Used in CRT glass and ferrite magnets.
SrCl₂	Strontium Chloride	Cl = -1; 2 Cl = -2; neutral: Sr + (-2) = 0 → Sr = +2	Freely soluble white salt. Used in toothpaste for sensitive teeth (desensitizing agent) and in red pyrotechnics.
Sr(OH)₂	Strontium Hydroxide	OH⁻ = -1; 2 OH = -2; neutral: Sr + (-2) = 0 → Sr = +2	Moderately soluble strong base. Used in the sugar industry to purify beet sugar (strontian process).
SrCO₃	Strontianite	CO₃ = -2; neutral: Sr + (-2) = 0 → Sr = +2	Mineral form of strontium carbonate; the main commercial ore of strontium. Named after Strontian, Scotland, where strontium was discovered.
SrSO₄	Celestine / Celestite	SO₄ = -2; neutral: Sr + (-2) = 0 → Sr = +2	The most abundant strontium mineral. Sparingly soluble (like BaSO₄); used to produce SrCO₃ for industrial use.
SrTiO₃	Strontium Titanate	Sr = +2; O = -2 (×3 = -6); Ti must be +4 to balance: (+2)+(+4)+(-6)=0 → Sr = +2	Cubic perovskite with very high dielectric constant. Used in electronics, as a diamond simulant, and in photocatalysis.
Sr(NO₃)₂	Strontium Nitrate	NO₃ = -1; 2 NO₃ = -2; neutral: Sr + (-2) = 0 → Sr = +2	Freely soluble oxidizing salt. Major ingredient in red signal flares and fireworks.
SrF₂	Strontium Fluoride	F = -1; 2 F = -2; neutral: Sr + (-2) = 0 → Sr = +2	Low solubility; used as an optical material in UV/IR windows and as a laser crystal host.

Common Uses

Red fireworks and emergency signal flares (Sr(NO₃)₂, SrCO₃)
Ferrite permanent magnets (SrO·6Fe₂O₃)
Sensitive-teeth toothpaste (SrCl₂ desensitizes dentin)
CRT glass (SrO absorbs X-rays emitted by the electron gun)
Perovskite electronics and photocatalysis (SrTiO₃)
Radioactive waste tracking (strontium-90 as a fission product marker)
Sugar refining via the strontian process (Sr(OH)₂)

Oxidation State Summary

State	Stability	Key Example	Notes
0	Elemental	Sr (metal)	Assigned by convention to elemental strontium; reacts with water and burns in air.
+2	Dominant	SrCl₂, SrO, SrCO₃	The only stable oxidation state in compounds; Sr²⁺ radius 118 pm; ionic radius drives solubility trends.

Group 2 Oxidation State Comparison

Element	Symbol	Oxidation States	Ionic Radius (pm)
Beryllium	Be	0, +2	45
Magnesium	Mg	0, +2	72
Calcium	Ca	0, +2	100
Strontium	Sr	0, +2	118
Barium	Ba	0, +2	135
Radium	Ra	0, +2	148

All Group 2 elements exhibit exclusively 0 and +2 oxidation states. Rows highlighted in blue indicate strontium.

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Summary

Reference for all strontium oxidation states (0 and +2) with example compounds, step-by-step assignments, and a compound lookup.

How it works

Click an oxidation state card (0 or +2) to open its detail panel.
The detail panel shows a description, example compounds with step-by-step assignments, and identification tips.
Use the Compound Lookup tab to select a known strontium compound and see the oxidation state of Sr 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 at the top.

Use cases

Students revising Group 2 oxidation state patterns for chemistry exams.
Chemistry teachers preparing reference materials on alkaline earth metals.
Researchers checking the oxidation state of strontium in a specific reagent or mineral.
Radiochemists working with strontium-90, a radioactive fission product.
Materials scientists working with strontium titanate (SrTiO₃) or other perovskites.
Learners comparing oxidation-state trends across Group 2 (Be, Mg, Ca, Sr, Ba, Ra).

Frequently Asked Questions

Last updated: 2026-07-08 · Reviewed by Nham Vu