rubidium (Rb)

Rubidium is a soft, silvery-white, metallic element belonging to the family of alkali metals. It was discovered in 1861 in Heidelberg by Robert Bunsen and Gustav Kirchhoff, by spectroscopic examination of the mineral lepidolite; its name is derived from the Latin rubidus, meaning "red."

Rubidium is the 23rd most abundant element in the Earth's crust, and is found as a minor constituent of potassium and cerium minerals, notably pollucite, carnallite, leucite and lepidolite. Metallic rubidium, prepared by electrolysis of the chloride or reduction of the carbonate, is used in electron tubes and photoelectric cells, and its salts in making special glasses and ceramics. Chemically, it resembles sodium but is more reactive, igniting in air and reacting violently with water. It forms amalgams with mercury and alloys with gold, cesium, potassium, and sodium. Rubidium colors a flame yellowish-violet. Its most common, and only stable, isotope is 85Rb (72.15%); three other isotopes are all radioactive. Rubidium-81 provides a useful source of krypton-81m for use in ventilation-perfusion scanning. It has a half-life of about 4 hours and decays into krypton-81m, emitting radiation as it does so.


Rubidium. Credit: RSC


atomic number 37
relative atomic mass 85.468
electron configuration [Kr]5s1
electron affinity -46.9 (M-M-)/kJ mol-1
melting point 38.89°C (102°F)
boiling point 688°C (1,270°F)