Title: Rubidium
CAS Registry Number: 7440-17-7
Literature 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, T½ 4.88´1010 yr, b- 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. 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. Keep under benzene, petroleum, or other liq not containing oxygen.
Melting point: mp 39°
Boiling point: bp 688°
Density: d20 1.532
Use: In making rubidium salts; as a reagent in making zeolite catalysts; in photoelectric cells.

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