Caesium Electron Configuration

Interactive reference for caesium's electron configuration ([Xe] 6s¹), orbital diagram, and key atomic properties.

Use the Caesium Electron Configuration

Z = 55 Cs Caesium

Caesium — Electron Configuration

Atomic number 55 · Alkali metal · Period 6, Group 1 · s-block

[Xe] 6s¹ 55 electrons 1 valence e⁻ +1 oxidation state

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
4s s orbital, shell n=4 2 2 4s²
3d d orbitals, shell n=3 10 10 3d¹⁰
4p p orbitals, shell n=4 6 6 4p⁶
5s s orbital, shell n=5 2 2 5s²
4d d orbitals, shell n=4 10 10 4d¹⁰
5p p orbitals, shell n=5 6 6 5p⁶
6s s orbital, shell n=6 1 2 6s¹
Total 55

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4p⁶ 5s² 4d¹⁰ 5p⁶ 6s¹

All 12 subshells written explicitly.

Noble-Gas Shorthand

[Xe] 6s¹

[Xe] = the filled 54-electron xenon core.

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) — 6s¹ 1 / 72 electrons (1%)

Shell 6 can hold up to 72 electrons by the 2n² formula; caesium uses only the first 6s¹ slot.

Summary

Caesium (Cs) has atomic number 55 and the ground-state electron configuration [Xe] 6s¹ — a single valence electron in the sixth shell that makes it the most electropositive stable element. This tool provides a full subshell table, noble-gas shorthand, orbital box diagram, and quantum numbers for all 55 electrons, along with key physical and chemical data. It is a reliable quick-reference for chemistry students, teachers, and anyone studying the alkali metals or periodic trends.

How it works

  1. The Aufbau principle fills orbitals from lowest to highest energy.
  2. Caesium's 55 electrons fill the xenon core (1s through 5p) plus one electron in 6s.
  3. The noble-gas shorthand [Xe] 6s¹ replaces the 54-electron xenon core with [Xe] in brackets.
  4. The single 6s¹ electron is the lone valence electron responsible for Cs⁺ ion formation.
  5. The orbital diagram shows the 6s subshell with one unpaired electron; all inner subshells are completely filled.
  6. The element facts tab lists physical properties, ionization energy, and common uses of caesium.

Use cases

  • Quick-reference for chemistry homework or exam review on electron configurations.
  • Visualize how the Aufbau principle fills s, p, and d subshells across six shells.
  • Understand why caesium is the most reactive stable alkali metal (low ionization energy, one valence electron).
  • Compare caesium to lighter alkali metals (Li, Na, K, Rb) in group 1 periodic trends.
  • Learn how the 6s¹ configuration explains Cs⁺ ion formation and +1 oxidation state.
  • Teaching aid for atomic structure, periodic trends, and group 1 chemistry.
  • Verify quantum numbers for caesium's outermost electron.

Frequently Asked Questions

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