Rubidium
alkali metal · period 5 · group 1 (alkali metals (and hydrogen)) · s-block
Rubidium is the chemical element with the symbol Rb and atomic number 37. Rubidium is a very soft, silvery-white metal in the alkali metal group.
What the numbers say
At standard temperature and pressure Rubidium is a solid, sitting in period 5, group 1 of the s-block.
Its melting point of 312 K (39 °C) is the 93rd highest of the 110 elements with a measured value — mid-range among the elements.
At 1.532 g/cm³ it is the 82nd densest of 96 elements with a quoted density.
Pauling electronegativity is 0.82. Paired with oxygen (3.44) that is a difference of 2.62, which puts the bond predominantly ionic — expect a stable oxide ceramic.
In the solid state it takes a body-centered cubic structure — BCC packing is stronger but shows a ductile-to-brittle transition as temperature drops.
It is reported in 2 oxidation states (-1, 1), which sets how many distinct compounds and phases it can form.
First identified in 1861.
Crystal structure
Solid Rubidium adopts a Body-centered Cubic arrangement, in the Cubic (isometric) system — axes a = b = c, angles α = β = γ = 90°. Symmetry controls the anisotropy of stiffness and thermal expansion, and the available slip systems set how far the metal deforms before it fractures.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Rb — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 18 · N 8 · O 1
Properties
| Atomic number | 37 |
|---|---|
| Atomic mass | 85.46783 u |
| Series | alkali metal |
| Group | 1 |
| Period | 5 |
| Block | s-block |
| Phase at STP | Solid |
| Density | 1.532 g/cm³ |
| Melting point | 312.45 K (39 °C) |
| Boiling point | 961 K (688 °C) |
| Electronegativity (Pauling) | 0.82 |
| Electron configuration | [Kr] 5s¹ |
| Crystal structure | Body-centered Cubic |
| Oxidation states | -1,1 |
| Discovered | 1861 |
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See Rb in context with all 118 elements.
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