What is the electron configuration of barium?

Barium (Ba, Z=56) has the ground-state electron configuration 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s². Its 56 electrons fill twelve subshells across six principal shells.

What is the noble-gas shorthand for barium?

The condensed (noble-gas) notation is [Xe] 6s², where [Xe] stands for the filled xenon core — 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ — containing 54 electrons.

Why does barium form a +2 ion?

Barium loses its two 6s valence electrons to achieve the stable [Xe] noble-gas core (54 electrons), forming Ba²⁺. The +2 state is the only common oxidation state for barium.

How many valence electrons does barium have?

Barium has 2 valence electrons, both in the 6s subshell. This is characteristic of all Group 2 alkaline earth metals.

What block and period is barium in?

Barium is in Period 6, Group 2 (IIA), and belongs to the s-block of the periodic table. It is the fifth alkaline earth metal, below strontium.

Is barium radioactive?

Naturally occurring barium is not radioactive. It has seven stable isotopes, with Ba-138 being the most abundant (71.7%). Several artificial barium radioisotopes exist, but they are not found in nature.

What are the quantum numbers for barium's outermost electrons?

The two 6s electrons have: n=6, l=0, mₗ=0, and mₛ=+½ for the first and mₛ=−½ for the second. Both occupy the single 6s orbital with opposite spins.

Barium Electron Configuration

Name: Barium Electron Configuration
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Author: Nham Vu

Interactive reference for barium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s²), orbital diagram, quantum numbers, and key properties.

Z = 56 Ba Barium

Barium — Electron Configuration

Atomic number 56 · Alkaline earth metal · Period 6, Group 2 · s-block

[Xe] 6s² 56 electrons 2 valence e⁻ +2 oxidation state

Subshell Breakdown

Subshell	Type	Electrons	Capacity	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
4d	d orbitals, shell n=4	10	10	4d¹⁰
5s	s orbital, shell n=5	2	2	5s²
5p	p orbitals, shell n=5	6	6	5p⁶
6s	s orbital, shell n=6	2	2	6s²
Total		56

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s²

All 12 subshells written explicitly — 56 electrons total.

Noble-Gas Shorthand

[Xe] 6s²

[Xe] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ (54 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 4d¹⁰ 18 / 32 electrons (56%)

Shell 5 (n=5) — 5s² 5p⁶ 8 / 50 electrons (16%)

Shell 6 (n=6) — 6s² 2 / 72 electrons (3%)

Shell 4 can hold 32 electrons (4s + 4p + 4d + 4f); barium uses 18 of those slots. Shell 6 holds only the 2 valence electrons.

Orbital Box Diagram

Each box = one orbital. Paired arrows = opposite spins (+½ up, −½ down). Inner subshells (1s through 5p) are all fully filled.

filled

valence electrons (paired, 6s²)

Opposing arrows represent paired electrons with opposite spins (+½ and −½). All subshells of barium are fully paired — it is diamagnetic with no unpaired electrons.

Quantum Numbers — Valence Electrons (6s²)

Electron #	n	l	mₗ	mₛ	Subshell
55	6	0	0	+½	6s
56	6	0	0	−½	6s

n = principal; l = azimuthal (0 = s subshell); mₗ = magnetic; mₛ = spin. Inner 54 electrons follow the same pattern for their respective subshells.

Summary

Interactive reference for barium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 5s² 5p⁶ 6s²), orbital diagram, quantum numbers, and key properties.

How it works

The Aufbau principle fills subshells from lowest to highest energy (1s → 2s → 2p → 3s … → 6s).
Barium's 56 electrons fill twelve subshells across six principal shells.
The 3d and 4d subshells each hold 10 electrons — the d-block contribution that sets barium apart from lighter alkaline earth metals.
The outermost subshell is 6s², giving barium 2 valence electrons and a typical +2 oxidation state.
Noble-gas notation compresses the inner 54 electrons into [Xe], leaving only the valence 6s² exposed.
The three tabs let you explore the subshell table, orbital box diagram, and element facts separately.

Use cases

Quick reference for chemistry homework or exam prep on Period 6 elements.
Visualize how the d-block fills before the 6s subshell in heavier alkaline earth metals.
Understand why barium always forms a +2 ion by losing both 6s electrons.
Compare barium to lighter Group 2 members — magnesium, calcium, strontium — to see periodic trends.
Study how the xenon noble-gas core stabilizes barium's inner electron structure.
Teaching aid for introductory atomic structure, periodic trends, and s-block chemistry lessons.
Verify quantum numbers for barium's two valence electrons.

Frequently Asked Questions

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