Rubidium Electron Configuration

Reference for rubidium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹), abbreviated as [Kr] 5s¹, with orbital diagram, quantum numbers, and element facts.

Z = 37 Rb Rubidium

Rubidium — Electron Configuration

Atomic number 37 · Alkali metal · Period 5, Group 1 · s-block

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹ [Kr] 5s¹ 37 electrons 1 valence e⁻

Subshell Breakdown

Subshell Type Electrons Max 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
5s s orbital, shell n=5 1 (valence) 2 5s¹
Total 37

Full Configuration

1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹

All nine subshells written explicitly.

Noble-Gas Shorthand

[Kr] 5s¹

[Kr] = 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ (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) — 5s¹ 1 / 50 electrons (2%)

Shell 4 can hold up to 32 electrons (4s + 4p + 4d + 4f). Rubidium uses only 8 of those slots. Shell 5 holds a single valence electron in the 5s orbital.

Summary

Reference for rubidium's electron configuration (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹), abbreviated as [Kr] 5s¹, with orbital diagram, quantum numbers, and element facts.

How it works

  1. The Aufbau principle fills orbitals from lowest to highest energy.
  2. Rubidium's 37 electrons fill nine subshells: 1s, 2s, 2p, 3s, 3p, 3d, 4s, 4p, then 5s.
  3. The 3d subshell (10 electrons across five orbitals) is filled before the 4s and 4p in the Aufbau order.
  4. After the completed [Kr] core (36 electrons), the 37th electron occupies the 5s orbital alone.
  5. Noble-gas notation replaces the inner 36 electrons with [Kr], leaving just 5s¹ visible.
  6. The single unpaired 5s¹ electron is responsible for rubidium's +1 oxidation state in all known compounds.

Use cases

  • Quick reference for chemistry homework or exam review on alkali metals.
  • Verify the electron configuration when comparing Period 4 potassium to Period 5 rubidium.
  • Understand why rubidium has exactly one valence electron and forms only the +1 cation.
  • Teaching aid for Period 5 Aufbau ordering and the role of the filled 3d subshell.
  • Explore how the [Kr] abbreviated notation works for elements beyond krypton.
  • Compare rubidium to its neighbors strontium (below, Group 2) and krypton (noble gas above).

Frequently Asked Questions

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