Rb Rubidium

Quick answerRubidium (Rb) is an alkali metal with atomic number 37 and an atomic mass of 85.468 (2023), in group 1, period 5. It was discovered by Robert Bunsen and Gustav Kirchhoff in 1861. It is used for atomic clocks and GPS satellites. Its electron configuration is [Kr] 5s1.

Rubidium is a soft metal so reactive it ignites in air, used in atomic clocks, GPS satellites, and research lasers.

Key facts

Symbol	Rb
Atomic number	37
Atomic mass	85.468 (IUPAC standard atomic weight, 2023)
Category	alkali metal
Group	1
Period	5
Block	s-block
Electron configuration	[Kr] 5s1
Discovered	Robert Bunsen and Gustav Kirchhoff, 1861
Uses	atomic clocks, GPS satellites, research lasers, electronics, medical imaging

Quick quiz

Three questions from the facts on this page. No sign-up, no score is saved.

1. What is the chemical symbol of Rubidium?

K Rb Na Li

2. What is the atomic number of Rubidium?

38 37 39 36

3. Which category does Rubidium belong to?

transition metal halogen alkali metal noble gas

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Keep exploring

• Periodic table — all 118 elements
• Lithium (Li) — another alkali metal, atomic number 3
• Sodium (Na) — another alkali metal, atomic number 11
• Potassium (K) — another alkali metal, atomic number 19
• Caesium (Cs) — another alkali metal, atomic number 55
• Francium (Fr) — another alkali metal, atomic number 87

Sources & last updated

• CIAAW — Standard Atomic Weights
• PubChem Periodic Table
• Wikipedia — Timeline of chemical element discoveries

Last updated: 2026-11-12. Figures are shown with their year; where sources disagree, the value is left out rather than estimated.