The name rubidium comes from the Latin word rubidium, meaning "deepest red". This refers to the red flame it produces when burned. This element is highly reactive, and ignites on contact with air. In contact with water, it reacts vigorously, producing hydrogen gas and much heat.

Rubidium is not only found in a few minerals, but is widespread in small quantities in a wide range of minerals, such as leucite and polucite. The pure metal is obtained mainly from the mineral lepidolite. Another mineral called rubicline has even more rubidium, but it is very rare. Rubidium atoms are sensitive to light and can be used in photoelectric cells and night vision equipment.

This element has radioactive forms, which can be used to date the age of rocks. When injected into a patient's body, rubidium targets tumors, which show up clearly on PET (positron emission tomography) scans. Rubidium is also used by light-sensitive electronics called photomultipliers, and in the manufacture of insulators for high-voltage cables and some special types of glass.

Summary of properties (Rb)

Atomic weight85.4678(3)
Discoverer (year)Bunsen, Robert Wilhelm & Kirchhoff, Gustav Robert (1861)
Natural formmetallic solid (body centered cubic)
Electron configuration[Kr] 5s1
Melting point (ºC)39
Boiling point (ºC)688
Abundance in earth's crust (ppm)90
Isotope (abundance)85Rb (72.17), 87Rb (27.83)
Density g/cm31.63
Van der Waals radius (pm)303
Covalent radius (pm)215
Electronegativity (Pauling)0.82
Vaporization enthalpy (kJ/mol)69.20
Enthalpy of fusion (kJ/mol)2.19
Specific heat capacity (J/g·K) at 25ºC and 1 atm0.36
Thermal conductivity (W/cm·K) at 25ºC and 1 atm0.580
Oxidation state+1
Electron affinity (eV)0.49
1st Ionization potential (eV)4.1771

Back to the Periodic Table of the Elements.