Rubidium (Rb)

Soft, silvery metal

Rubidium is an extremely reactive, soft metal used in atomic clocks and GPS satellites, and with a single 5s¹ electron, rubidium has an even lower ionization energy (403 kJ/mol) than potassium. Its hyper-fine transition frequency (6.834 GHz) is used as a secondary time standard.

Key metrics

Density1.53g/cm³

Melting point312K

Boiling point961K

Electronegativity0.82Pauling

Discovery

1861discovered

Discovered by: Robert Bunsen
Reactivity profile: Violently reacts with water
Reactivity: High
Bonding: Metallic

Electron configuration

\textcolor{#6b7280}{[Kr]}\; \textcolor{#ef4444}{5_{s}^{1}}

[Kr] 5s1

Wave function

\Psi_{\text{Rb}} \approx \frac{1}{\sqrt{37!}} \det \left| \chi_1(\mathbf{r}_1) \dots \chi_{37}(\mathbf{r}_{37}) \right|

Probability density $|\Psi|^2$ across the Rb valence shell.

Crystal structure

Body-Centered Cubic

Lattice constantsa = 1.00

Cell anglesα = β = γ = 90°

Coordination number8

Atoms per cell2

Atomic packing factor0.68

Physical properties

Atomic radius: 265 pm
Ionization energy: 403 kJ/mol
Electron affinity: 47 kJ/mol
Crystal structure: Body-centered cubic (bcc)

Oxidation states

Acid/base

Basic

Strongly acidicStrongly basic

State at 25 °CSolid

312 K961 K298 K

Emission spectrum

3 transitions

380450500550600650700780

VioletBlueGreenYellowRed

421.6nmRb I (violet)Violet30%

780.0nmRb I (red)IR100%

794.8nmRb I (red)IR80%

Dominant line 780.0 nmRange 422–795 nmTransitions 3