What is the electron configuration of strontium?

Strontium (Sr, Z=38) has the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s². Its 38 electrons fill nine subshells across five principal shells.

What is the noble-gas shorthand for strontium?

The condensed notation is [Kr] 5s², where [Kr] represents the filled 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ core shared with krypton (Z=36).

How many valence electrons does strontium have?

Strontium has 2 valence electrons, both in the 5s subshell. This matches its Group 2 (alkaline earth metal) membership and explains why it forms a 2+ ion in compounds.

Why does strontium use [Kr] as its noble-gas core?

Krypton (Z=36) is the noble gas immediately before strontium in the periodic table. Its 36 electrons form a complete, stable inner core. Strontium adds 2 electrons on top of that core, so [Kr] 5s² is the most compact way to write the configuration.

What oxidation state does strontium commonly adopt?

Strontium almost exclusively forms the +2 oxidation state by losing both 5s electrons. The resulting Sr²⁺ ion has the stable [Kr] electron configuration. A +1 state is theoretically possible but extremely rare.

What block and period is strontium in?

Strontium is in Period 5, Group 2, and belongs to the s-block of the periodic table. As an alkaline earth metal it is highly reactive and always found as a compound in nature.

How does strontium's configuration differ from calcium's?

Calcium (Z=20) is [Ar] 4s²; strontium (Z=38) is [Kr] 5s². Strontium has one extra full period of electrons (including the 3d¹⁰ and 4p⁶ subshells) and a larger atomic radius, but both elements have exactly 2 valence s-electrons and behave similarly chemically.

Strontium Electron Configuration

Name: Strontium Electron Configuration
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Reference for strontium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s²), orbital diagram, quantum numbers, and element data.

Z = 38 Sr Strontium

Strontium — Electron Configuration

Atomic number 38 · Alkaline earth metal · Period 5, Group 2 · s-block

[Kr] 5s² 38 electrons 2 valence e⁻ Shells: 2, 8, 18, 8, 2

Subshell Breakdown

Subshell	Type	Electrons	Max	Notation
1s	s orbital, shell n=1	2	2	1s²
2s	s orbital, shell n=2	2	2	2s²
2p	p orbitals, shell n=2	6	6	2p⁶
3s	s orbital, shell n=3	2	2	3s²
3p	p orbitals, shell n=3	6	6	3p⁶
3d	d orbitals, shell n=3	10	10	3d¹⁰
4s	s orbital, shell n=4	2	2	4s²
4p	p orbitals, shell n=4	6	6	4p⁶
5s	s orbital, shell n=5	2(valence)	2	5s²
Total		38

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s²

All nine subshells written explicitly.

Noble-Gas Shorthand

[Kr] 5s²

[Kr] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ (krypton core, 36 electrons).

Shell Fill Summary

Shell 1 (n=1) — 1s² 2 / 2 electrons (100%)

Shell 2 (n=2) — 2s² 2p⁶ 8 / 8 electrons (100%)

Shell 3 (n=3) — 3s² 3p⁶ 3d¹⁰ 18 / 18 electrons (100%)

Shell 4 (n=4) — 4s² 4p⁶ 8 / 32 electrons (25%)

Shell 5 (n=5) — 5s² 2 / 50 electrons (4%)

Shell 4 can hold up to 32 electrons (4s + 4p + 4d + 4f). Strontium uses 8 of those 32 slots (4s² 4p⁶); the 4d and 4f subshells remain empty.

Orbital Box Diagram

The [Kr] core (1s² through 4p⁶) is shown collapsed. Only the valence region is expanded.

[Kr]

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ — 36 electrons in filled krypton core

2 electrons (paired) — valence subshell, filled

Each box represents one orbital. Opposing arrows show paired electrons with opposite spins (+½ and −½). Strontium's two 5s valence electrons are paired in the single 5s orbital, completing the alkaline-earth pattern of Group 2.

Quantum Numbers — Valence Electrons (5s²)

Electron #	n	l	mₗ	mₛ	Subshell
37	5	0	0	+½	5s
38	5	0	0	−½	5s

n = principal quantum number; l = azimuthal (l=0 → s); mₗ = magnetic; mₛ = spin. Electrons 1–36 fill the [Kr] core with identical subshell-by-subshell patterns up through 4p⁶.

Summary

Reference for strontium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s²), orbital diagram, quantum numbers, and element data.

How it works

The Aufbau principle fills orbitals from lowest to highest energy.
Strontium's 38 electrons fill through the 3d subshell before the 4p and 5s subshells.
The inner 36 electrons match the configuration of krypton, the preceding noble gas.
Two remaining electrons occupy the 5s subshell, giving strontium 2 valence electrons.
Noble-gas notation replaces the krypton core with [Kr]: [Kr] 5s².
The tabs below let you explore the full configuration, orbital diagram, and element data.

Use cases

Quick reference for chemistry homework or exam review on alkaline earth metals.
Understand why strontium is reactive and forms Sr²⁺ ions by losing both 5s electrons.
Compare strontium to calcium and barium within Group 2.
Teaching aid for introductory atomic structure and electron configuration lessons.
Verify quantum numbers for strontium's valence electrons.
Explore the role of the [Kr] core in period-5 element configurations.
Use as a cross-check alongside a periodic table for period 5 building-up order.

Frequently Asked Questions

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