Atomic Number: 85
Atomic Weight: 209.9871
Discovery: D.R. Corson, K.R. MacKenzie, E. Segre 1940 (United States)
Electron Configuration: [Xe] 6s2 4f14 5d10 6p5
Word Origin: Greek astatos, unstable
Isotopes: Astatine-210 is the longest-lived isotope, with a half-life of 8.3 hours. Twenty isotopes are known.
Properties: Astatine has a melting point of 302°C, an estimated boiling point of 337°C, with probable valences of 1, 3, 5, or 7. Astatine possesses characteristics common to other halogens. It behaves most similarly to iodine, except that At exhibits more metallic properties. The interhalogen molecules AtI, AtBr, and AtCl are known, although it has not been determined whether or not astatine forms diatomic At2. HAt and CH3At have been detected. Astatine probably is capable of accumulating in the human thyroid gland.
Sources: Astatine was first synthesized by Corson, MacKenzie, and Segre at the University of California in 1940 by bombarding bismuth with alpha particles. Astatine may be produced by bombarding bismuth with energetic alpha particles to produce At-209, At-210, and At-211. These isotopes can be distilled from the target upon heating it in air. Small quantities of At-215, At-218, and At-219 occur naturally with uranium and thorium isotopes. Trace amounts of At-217 exist in equilibrium with U-233 and Np-239, resulting from the interaction between thorium and urainuam with neutrons. The total amount of astatine present in the Earth's crust is less than 1 ounce.
Element Classification: halogen
Melting Point (K): 575
Boiling Point (K): 610
Covalent Radius (pm): (145)
Ionic Radius: 62 (+7e)
Pauling Negativity Number: 2.2
First Ionizing Energy (kJ/mol): 916.3
Oxidation States: 7, 5, 3, 1, -1
References: Los Alamos National Laboratory (2001), Crescent Chemical Company (2001), Lange's Handbook of Chemistry (1952), CRC Handbook of Chemistry & Physics (18th Ed.)
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