Rubidium (Rb): Electron Configuration, Properties and Uses
Rubidium (Rb): Electron Configuration, Properties and Uses
Electron configuration [Kr] 5s1 · group 1 · period 5 · Ar 85.468
Rubidium data
- Atomic number
- 37
- Relative atomic mass
- 85.468
- Group
- 1
- Period
- 5
- Block
- s
- Category
- Alkali metal
- Electron configuration
- [Kr] 5s1
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1
- Electrons per shell
- 2, 8, 18, 8, 1 (K L M N O)
- Valence electrons
- 1
- Electronegativity (Pauling)
- 0.82
- First ionisation energy
- 4.177 eV
- Atomic radius (van der Waals)
- 303 pm
- State at room temperature
- Solid
- Melting point
- 39.3 °C
- Boiling point
- 688 °C
- Density
- 1.53 g/cm³
- Common oxidation states
- +1
- Discovered
- 1861
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 8 · O 1
Orbital diagram (outer electrons)
About rubidium
With atomic number 37, rubidium (Rb) has 37 protons in its nucleus and 37 electrons as a neutral atom. It is an alkali metal in group 1, period 5, s-block. The element was discovered in 1861. Rubidium is a solid that melts at 39.3 °C, just above body temperature.
Rubidium electron configuration
The electron configuration of rubidium is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1, or in short [Kr] 5s1. Its electrons occupy 5 shells: K = 2, L = 8, M = 18, N = 8, O = 1. Rubidium has 1 valence electron in the O shell (5s1), which is why it sits in group 1. When it forms cations, electrons leave the outermost subshell first: Rb+ = [Kr] (like krypton).
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p6(36) → 5s1(37)
Uses of rubidium
In industry and the laboratory, rubidium turns up in many places, for example rubidium atomic clocks, photocells and Bose-Einstein condensate research.
Safety
Like the other alkali metals, rubidium reacts violently with water and air, so it is stored under oil or inert gas. Always read the safety data sheet (SDS) before working with a chemical.
Other elements in group 1
Frequently asked questions
What is the electron configuration of rubidium?
The electron configuration of rubidium (Rb, atomic number 37) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s1, or [Kr] 5s1 in short. By shell: 2, 8, 18, 8, 1.
How many valence electrons does rubidium have?
Rubidium has 1 valence electron.
Which group and period is rubidium in?
Rubidium is in group 1, period 5, s-block.
What is the atomic mass of rubidium?
The relative atomic mass of rubidium is 85.468. Use it to calculate molar mass with the molar mass calculator.
Prepare solutions with analytical-grade reagents
AMI Scientific is one of the official TCI distributors in Indonesia. Reagents with lot CoA & SDS, formal quotations and tax invoices for universities and laboratories.
Other formulas & calculators: molarity, mole, molality, normality, dilution, titration, pH, buffer, molar mass, ppm, mole fraction, mass percent, periodic table, chemical MSDS.
