8095. Radon

Nomenclature

CAS number: 10043-92-2

Description and references

Rn; at. no. 86. Obsolete synonyms: niton, symbol Nt, and radium emanation or emanation, symbol Em. Group VIIIA (18), also known as Group 0. A noble gas characterized by an electronic structure in which the outer p subshell is entirely filled. No stable nuclides; naturally occurring isotope (mass number): 222 (longest-lived known isotope, T 1/2 3.825 days, rel. at. mass 222.0176, α-emitter, member of decay chain of 238U). Known artificial radioactive isotopes: 200-221, 223-226. Isotope 220Rn (T 1/2 55.6 sec, α-emitter, rel. at. mass 220.0114, formed in decay chain of 232Th), unofficial name Thoron, symbol Tn, was discovered by Owens and Rutherford in 1900. 222Rn was discovered by Dorn in 1900 and isolated by Rutherford and Sody in 1902. Isotope 219Rn (T 1/2 3.96 sec, α-emitter, formed in decay chain of 235U), unofficial name actinon, symbol An, was discovered by Debièrne and Giesel in 1902. Concentration in air: 6 × 10-14 ppm by vol; in igneous rock of the earth's crust: 1.7 × 10-10 ppm by wt. Prepn of fluoride: Fields et al., J. Am. Chem. Soc. 84, 4164 (1962); Stein, Science 168, 362 (1970). Prepn of gas from radium salt: Jennings, Russ, Radon: Its Technique and Use (Murray, London, 1948) pp 79-95. Reviews of chemistry and compds: Argon, Helium and the Rare Gases, G. A. Cook, Ed. (Interscience, New York, 1961); Haissinsky, Adloff, Radiochemical Survey of the Elements (Elsevier, New York, 1965) pp 126-128; Cockett, Smith, “The Monatomic Gases” in Comprehensive Inorganic Chemistry vol. 1, J. C. Bailar, Jr. et al., Eds. (Pergamon Press, Oxford, 1973) pp 139-211; Bartlett, Sladky, ibid. pp. 213-330; S.-C. Hwang, W. R. Weltmer, Jr. in Kirk-Othmer Encyclopedia of Chemical Technology vol. 13 (John Wiley & Sons, 4th ed., 1995) pp 1-38; G. J. Schrobilgen, J. M. Whalen, ibid. pp 38-53; Chemistry of the Elements, N. N. Greenwood, A. Earnshaw, Eds. (Pergamon Press, New York, 1984) pp 1042-1059. Reviews of sources and health effects of indoor radon exposure: E. P. Radford, Environ. Health Perspect. 62, 281-287 (1985); D. L. Henshaw, Contemp. Phys. 34, 31-48 (1993).

Properties

Colorless, odorless, tasteless, inert, monatomic gas; will form compds with highly electronegative elemnts such as O, F, Cl. Soly of gas in water (20°) 230 cm3/l water. Soluble in organic solvents. Strongly adsorbed on various surfaces. Heat capacity at 25° and 1 atm: 4.9860 cal/g-atom/K. Triple point temp 202 K, press 70 kPa. Critical temp 378 K, critical press 6280 kPa. Gas: d0 (101.3 kPa) 9.73 kg/m3. Liquid: normal bp -62°, d (normal bp) 4400 kg/m3, heat of vaporization (normal bp) 18,100 J/mol. Heat of fusion (triple point) 3247 J/mol. Solid form exists as face-centered cubic crystals at normal pressure.

Caution

Toxicity due to ionizing radiation (α-emitter). Increased incidences of lung cancer have been reported due to occupational exposure to high doses of radon, especially in hard rock miners. Max permissible concn of 222Rn in air: 10-8 μ-Curie/cc: Natl. Bur. Stand. Handb. 69, 79 (1959). The U.S. EPA has established an action level of 4 pCi/l (0.02 working levels) for home indoor radon and radon decay product measurements. See: Interim Protocols for Screening and Follow-up Radon and Radon Decay Product Measurements (PB89-224265, EPA-520/1-86-014-1, 1987) 22 p. Radon and its isotopic forms, 222Rn and 220Rn, are listed as known human carcinogens: Report on Carcinogens, Eleventh Edition (PB2005-104914, 2004) p III-152

Use

To initiate and influence chemical reactions, as a surface label in the study of surface reactions; in the determination of radium or thorium; in the study of the behavior of filters; in combination with Be or other light materials as a source of neutrons.

Therapeutic Category

Antineoplastic (radiation source).

Keywords

Antineoplastic (Radiation Source)