8282. Rubidium

Nomenclature

CAS number: 7440-17-7

Description and references

Rb; at. wt 85.4678; at. no. 37; valence 1. Group IA (1). Alkali metal. Widely distributed in very small quantities in earth's crust: 0.0034% by wt. Naturally occurring isotopes: 85 (72.15%); 87 (27.85%); 87Rb is radioactive, T 1/2 4.88×1010 yr, β- emitter. Artificial isotopes (mass nos.): 74-102. Found with other alkali metals in rhodizite (borate), lepidolite (aluminosilicate), rubidium carnallite (chloride); in sea water; in mineral springs and salt lakes. Discovered by Bunsen and Kirchhoff in 1861. Prepn: Hackspill, Helv. Chim. Acta 11, 1003 (1928). Review: Whaley, “Sodium, Potassium, Rubidium, Cesium and Francium” in Comprehensive Inorganic Chemistry vol. I, J. C. Bailar Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 369-529; Chemistry of the Elements N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 75-116; F. S. Wagner in Kirk-Othmer Encyclopedia of Chemical Technology vol. 21 (Wiley-Interscience, New York, 4th ed., 1997) pp 591-600.

Properties

Lustrous, silvery-white, soft metal; body-centered cubic structure; rapidly tarnishes on exposure to air. mp 39°. bp 688°. d20 1.532. Specific heat 0.0802 cal/g deg. One of the most active metals. E° (aq) Rb/Rb+ 2.924 V. Emits characteristic red-violet color (780.0 nm) in flame. Chemical properties closely resemble potassium. Dangerous when wet. Keep under benzene, petroleum or other liquid not containing oxygen. Reacts violently with water, ice, steam, lower alcohols, chlorinated hydrocarbons. Ignites spontaneously in oxygen; when molten readily takes fire in the air. Reacts vigorously with the halogens. Forms a series of solid solns with potassium, cesium, sodium. Combines vigorously with mercury.

Use

In making rubidium salts; as a reagent in making zeolite catalysts; in photoelectric cells.