Cesium
Title: Cesium
CAS Registry Number: 7440-46-2
Additional Names: Caesium
Literature References: Cs; at. wt 132.9054519; at. no. 55; valence 1. Group IA (1). Alkali metal. Occurrence in earth's crust: 2.6 ppm. Naturally occurring isotope: 133Cs (100%); artificial isotopes (mass nos.): 112-132, 134-148. Occurs in nature in the aluminosilicates, pollucite and lepidolite and in the borate, rhodizite. Acid digestion of pollucite ore is primary commercial source. Discovered by Bunsen and Kirchhoff in 1860. Prepn from pollucite: Inorg. Synth. 4, 5 (1953). 137Cs (T½ 30.07 years; b- 0.514, 1.176 MeV) is a product of atomic fission of uranium and an important constituent of radioactive fallout; decays to and reaches radioactive equilibrium with 137mBa (T½ 2.552 min; g 0.662 MeV). Review of cesium and its compounds: Whaley, "Sodium, Potassium, Rubidium, Cesium, and Francium" in Comprehensive Inorganic Chemistry vol. 1, 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; R. O. Burt in Kirk-Othmer Encyclopedia of Chemical Technology vol. 5 (Wiley-Interscience, New York, 4th ed., 1993) pp 749-764. Review of toxicology and human exposure: Toxicological Profile for Cesium (PB2004-104397, 2004) 310 pp.
Properties: Silver-white, ductile metal; body-centered cubic structure. mp 28.5°. bp 705°. d20 1.90. Specific heat (25°) 0.057 cal/g/°C. E°/v (aq) Cs/Cs+ -2.92. Electrical resistivity 36.6 micro-ohm cm at 30°. Mohs' hardness 0.2. Oxidizes rapidly in air; in moist air may ignite spontaneously to produce nonluminous reddish-violet flame. Emits characteristic blue color (455.5 nm) in flame. Reacts with water to form hydroxide with evolution of hydrogen which ignites spontaneously. Sol in liquid ammonia. Keep immersed in mineral oil.
Melting point: mp 28.5°
Boiling point: bp 705°
Density: d20 1.90
Use: In photoelectric cells, as a "getter" in vacuum tubes; in photoemitter devices, scintillation counters. Adsorbent in CO2 purifn; scavenger of gases and impurities in metallurgy. For doping catalysts. For construction and operation of one type of atomic clock based on the vibrational frequency (9,192.76 megacycles/sec) of 133Cs. 137Cs in process control instruments, sewage and sludge sterilization.

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