Title: Polonium
CAS Registry Number: 7440-08-6
Literature References: Po; at. no. 84; valence 4, occasionally 2, rarely 6. No stable nuclides. Isotopes range in mass number from 193-218; all are radioactive; 210 is naturally occurring. The first radioactive substance discovered by Mme. Curie in 1898. A product of disintegration of radium; one gram is contained in ~25,000 tons of pitchblende or in 7.5 kg radium that is more than 30 years old. Separated in form of a deposit on a bismuth plate immersed in a soln of the chloride: Marckwald, Ber. 35, 2285 (1902); using a silver, gold or nickel plate: Curie, Joliot, J. Chim. Phys. 28, 201 (1931); Haissinsky, ibid. 33, 97 (1936); Rollier, Gazz. Chim. Ital. 66, 797 (1936); Ziv, C. R. Acad. Sci. URSS 25, 743 (1939). Obtained in the metallic form by volatilization from nickel on a collodion film: Rollier et al., J. Chim. Phys. 4, 648 (1936). The only readily accessible isotope is the penultimate member of the radium decay series, 84210Po, also called Radium F (Ra-F). Decays by a-emission (T½ 138.4 days, rel. at. mass 209.9828) to 82206Pb. Comprehensive reviews: K. W. Bagnall, Chemistry of the Rare Radioelements (Butterworths, London, 1957); idem, Endeavour 22(86), 61 (May 1963); idem, "Selenium, Tellurium and Polonium" in Comprehensive Inorganic Chemistry vol. 2, J. C. Bailar, Jr., et al., Eds. (Pergamon Press, Oxford, 1973) pp 935-1008.
Properties: Two allotropic forms; coexist between 18° and 54°; d (a-form) 9.196; d (b-form) 9.398. mp 254°; bp 962°. Latent heat of vaporization: 24.597 kcal/mole. Resistivity: a-Po = 42 mohm-cm at 0°; b-Po = 44 mohm-cm at 0°. Physical properties: Maxwell, J. Chem. Phys. 17, 1288 (1949). Chemically resembles tellurium and bismuth. Forms a volatile, unstable hydride, PoH2. Forms a polonide, Na2Po; a carbonyl PoCO; a hydroxide Po(OH)4.
Melting point: mp 254°
Boiling point: bp 962°
Density: d (a-form) 9.196; d (b-form) 9.398
CAUTION: Radiation hazard; alpha emitter. Sol compds hazard to kidneys, spleen; insol, airborne compds hazard to lungs. Max permissible concn of insol 84210Po in air: 7 ´ 10-11 m-Curie/cc, Natl. Bur. Stand. Handb. 69, 79 (1959).

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