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.

Use the Rubidium Electron Configuration

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

Rubidium (Rb) is atomic number 37, a soft alkali metal in Period 5, Group 1. Its ground-state electron configuration is 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹, abbreviated as [Kr] 5s¹ using the krypton noble-gas core. The single 5s¹ valence electron makes rubidium highly reactive and gives it typical alkali-metal chemistry. This tool provides a subshell breakdown, orbital box diagram, quantum numbers for the 37 electrons, and key atomic properties.

How it works

  1. The Aufbau principle fills orbitals from lowest to highest energy.
  2. Rubidium's 37 electrons fill nine subshells in Aufbau order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p, then 5s.
  3. The 4s subshell fills before 3d; after 3d is complete, the 4p subshell fills to complete the [Kr] core.
  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 (adjacent, Group 2) and krypton (noble gas above).

Frequently Asked Questions

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