We use cookies and other tracking technologies to improve your browsing experience on our website, to show you personalized content and targeted ads, to analyze our website traffic, and to understand where our visitors are coming from. For more information, please review our cookie policy and privacy policy.
By choosing I Accept, you consent to our use of cookies and other tracking technologies.

Rubidium (Rb)

Rubidium is a chemical element of the periodic table with chemical symbol Rb and atomic number 37 with an atomic weight of 85.4678 u and is classed as alkali metal and is part of group 1 (alkali metal). Rubidium is solid at room temperature.

Rubidium in the periodic table

Atomic number37
Group1 (Alkali metal)
ClassificationAlkali Metal
AppearanceGrey white
Color Silver
Number of protons37 p+
Number of neutrons48 n0
Number of electrons37 e-
From Wikipedia, the free encyclopediaRubidium is a chemical element with symbol Rb and atomic number 37. Rubidium is a soft, silvery-white metallic element of the alkali metal group, with an atomic mass of 85.4678. Elemental rubidium is highly reactive, with properties similar to those of other alkali metals, such as very rapid oxidation in air.

Physical properties

Phase at STPSolid
Density1.532 g/cm3
Atomic weight85.4678 u

Thermal properties

Melting point312.45 K
39.3 °C
102.74 °F
Boiling point961 K
687.85 °C
1270.13 °F
Heat of vaporization69.2 kJ/mol

Atomic properties

Electronegativity (Pauling Scale)0.82
Electron affinity46.884 kJ/mol
Oxidation states−1, +1
(a strongly basic oxide)
Ionization energies
  1. 403 kJ/mol
  2. 2633 kJ/mol
  3. 3860 kJ/mol
  4. 5080 kJ/mol
  5. 6850 kJ/mol
  6. 8140 kJ/mol
  7. 9570 kJ/mol
  8. 13120 kJ/mol
  9. 14500 kJ/mol
  10. 26740 kJ/mol

Electron configuration for rubidium

Electron configuration
Shorthand configuration
[Kr] 5s1
Electron configuration
Full configuration
1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 5s1
Electron configuration chart
Electrons per shell2, 8, 18, 8, 1
Valence electrons 1
Valency electrons 1
Bohr model
RubidiumElectron shell for Rubidium, created by Injosoft ABRb
Figure: Shell diagram of Rubidium (Rb) atom.
Orbital Diagram

The history of Rubidium

DiscoveryRobert Bunsen, Gustav Kirchhoff (1861)
First isolationGeorge de Hevesy
Discovery of rubidium
Rubidium was discovered in 1861 by Robert Bunsen and Gustav Kirchhoff, in Heidelberg, Germany, in the mineral lepidolite through flame spectroscopy. Because of the bright red lines in its emission spectrum, they chose a name derived from the Latin word rubidus, meaning "deep red". The slight radioactivity of rubidium was discovered in 1908, but that was before the theory of isotopes was established in 1910, and the low level of activity (half-life greater than 1010 years) made interpretation complicated.


List of unique identifiers for Rubidium in various chemical registry databases
CAS Number7440-17-7
ChemSpider ID4512975
EC number231-126-6
PubChem CID Number5357696