Rubidium
[Kr] 5s¹ · 2 · 8 · 18 · 8 · 1
A soft alkali metal discovered spectroscopically from two deep red lines. Rubidium melts just above room temperature and serves in atomic clocks and in Bose–Einstein condensate experiments.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
Drag to rotate, scroll to zoom
Atomic properties
- Atomic number
- 37
- Atomic mass
- 85.468 а.е.м.
- Electron configuration
- [Kr] 5s¹
- Electrons per shell
- 2 · 8 · 18 · 8 · 1
- Block
- s-block
- Group
- Alkali metals
- Period
- 5
- Electronegativity (Pauling)
- 0.82
- Electronegativity (Allen)
- 0.71
- Atomic radius
- 265 pm
- Covalent radius
- 220 pm
- Van der Waals radius
- 303 pm
- Ionisation energy 1
- 403 kJ/mol
- Ionisation energy 2
- 2 633 kJ/mol
- Ionisation energy 3
- 3 860 kJ/mol
- Electron affinity
- 46.9 kJ/mol
- Common oxidation states
- +1
- Oxidation states
- -1, +1
Physical properties
- State at 25 °C
- solid
- Density
- 1.532 g/cm³
- Melting point
- 312.45 K · 39.3 °C
- Boiling point
- 961 K · 687.9 °C
- Speed of sound
- 1 300 m/s
Thermal properties
- Heat of fusion
- 2.19 kJ/mol
- Heat of vaporisation
- 69 kJ/mol
- Specific heat capacity
- 0.363 J/(g·K)
- Thermal conductivity
- 58.2 W/(m·K)
Mechanical properties
- Young's modulus
- 2.4 GPa
- Shear modulus
- 0.9 GPa
- Bulk modulus
- 2.5 GPa
- Poisson ratio
- no data
- Mohs hardness
- 0.3
- Brinell hardness
- 0.216 MPa
Electrical and magnetic properties
- Electrical resistivity
- 128 nΩ·m
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- body-centred cubic (bcc)
- Lattice constants
- a = 558.5 pm
Abundance
- In the crust
- 90 mg/kg
- In the ocean
- 0.12 mg/L
- In the universe
- 10 mg/kg
- In the human body
- 4.6 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 85Rb | 72.17 % | stable | — |
| 87Rb | 27.83 % | 49.21 Gyr | β− |
Rubidium-87 is radioactive with a 49-billion-year half-life and makes up 28 % of natural rubidium; rubidium–strontium dating is a mainstay of geochronology.
Discovery
- Year of discovery
- 1861
- Discovered by
- Robert Bunsen and Gustav Kirchhoff
- Where
- Germany
- Origin of the name
- from Latin rubidus (deep red), the colour of its spectral lines
History
Bunsen and Kirchhoff found rubidium in 1861 with the spectroscope they had just invented — the second element found by the new method, right after caesium.
Where it occurs
90 mg/kg of the crust, more than copper. It has almost no minerals of its own and follows potassium into lepidolite and carnallite.
How it is produced
As a by-product of extracting lithium from lepidolite. World output is measured in tonnes.
Role in living things
The body handles rubidium much as it handles potassium and accumulates it in cells, but no requirement is established and no deficiency is known.
Safety
Rubidium metal ignites spontaneously in air and reacts violently with water. Its salts are of low toxicity.
Uses
- Rubidium frequency standards — affordable atomic clocks for telecoms and navigation
- Making Bose–Einstein condensates and laser-cooling experiments
- Photocells and photomultipliers
- Rubidium-82 in cardiac PET imaging
Curiosities
- The world's first Bose–Einstein condensate, made in 1995, was rubidium-87.
- Rubidium is named from the Latin for deep red, after its spectral lines rather than the metal itself.
- Rubidium and caesium were the first elements ever found by spectral analysis.
- Natural rubidium is faintly radioactive because of ⁸⁷Rb.