About

Rubidium is a soft, silvery-white alkali metal that is highly reactive, capable of igniting spontaneously in air and reacting violently with water. It is used in specialized vacuum tubes to remove trace gases and is a key component in atomic clocks, which are the most accurate timekeeping devices known. It is also used in research into Bose-Einstein condensates.

Atomic Properties

Atomic Number37

Atomic Weight85.468 u

Neutrons (common)48

Electron Configuration[Kr] 5s¹

Full Configuration1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 5s¹

Electrons per Shell2, 8, 18, 8, 1

Electronegativity0.82

Electron Affinity46.886 kJ/mol

Oxidation States+1

Covalent Radius220 pm

Van der Waals Radius303 pm

Ionic Radius152 pm

Periodic Table Position

Group1

Period5

BlockS

Chemical SeriesAlkali metals

Physical Properties

State at STPsolid

Appearancesoft, silvery-white metallic solid

Crystal Structurebcc

Magnetic Orderingparamagnetic

Speed of Sound1,300 m/s

Poisson Ratio0.312

Thermal Properties

Melting Point312.46 K

Boiling Point961 K

Triple Point312.45 K

Thermal Expansion0 1/K

Thermal Conductivity58.2 W/(m·K)

Specific Heat0.363 J/(g·K)

Molar Heat31.06 J/(mol·K)

Heat of Fusion2.19 kJ/mol

Heat of Vaporization72.216 kJ/mol

Abundance

In Earth's Crust90 ppm

In Ocean0.12 ppm

In Solar System0.007 ppm

In Human Body9.7 ppm

In Universe0.01 ppm

Discovery

Discovered byRobert Bunsen & Gustav Kirchhoff

Discovery Year1,861

Occurrenceprimordial

CAS Number7440-17-7

Electron Configuration

Energy

↿⇂

↿

Isotopes of Rubidium

Symbol ▲	Mass (u) ▲	Abundance ▲	Half-life ▲	Decay Mode ▲
⁸³Rb	82.915110	—	86.2 d	Electron Capture
⁸⁴Rb	83.914385	—	32.82 d	Positron Emission, Electron Capture, Beta Minus Decay
⁸⁵Rb	84.911790	72.17%	Stable	Stable
⁸⁶Rb	85.911167	—	18.645 d	Beta Minus Decay
⁸⁷Rb	86.909180	27.83%	49.7 Gy	Beta Minus Decay

Interactive Visualization

Explore the 3D Bohr model of Rubidium in our interactive viewer.

View 3D Model of Rubidium