Rubidium

MELTING POINT: 39.5°C
BOILING POINT: 688°C
DENSITY: 1.532 g/cm³
MOST COMMON IONS: Rb⁺

Rubidium is a soft, silvery alkali metal that reacts explosively with water. The word rubidium is derived from "rubidus" (Latin for "deepest red"), due

to the deep red lines observed by Robert Bunsen and Gustav Kirchoff during their analysis of lepidolite ore using a spectroscope in 1861. Currently, rubidium metal is obtained via the electrolysis of molten RbCl or by treating molten RbCl with calcium and distilling the mixture. Rubidium is usually obtained as a by-product of lithium processing because it is found in low concentrations in the minerals lepidolite, carnallite, and pollucite, as well as in the brines at Searles Lake, California. It is the sixteenth most abundant element in Earth's crust (about 78 ppm). Rubidium is never found in its elemental state in nature. It is the second most electropositive element and will ignite in air (unlike Na and K). Rubidium burns yellow-violet in the flame test.

The demand for rubidium metal and its compounds is quite small. The metal is used as a getter to remove oxygen in vacuum tubes. The crystalline compound RbAg₄I₅ has a conductivity similar to dilute sulfuric acid, which may make it useful in batteries and other electrochemical applications. Rubidium carbonate, Rb₂CO₃, is used in the manufacture of specialized glasses.

Bibliography

Emsley, John (2001). Nature's Building Blocks: An A-Z Guide to the Elements. New York: Oxford University Press.

Greenwood, N. N., and Earnshaw, A. (1997). Chemistry of the Elements, 2nd edition. Boston: Butterworth-Heinemann.

Lide, David R., ed. (2000). CRC Handbook of Chemistry & Physics, 81st edition. New York: CRC Press.