Astatine Facts - Periodic Table of the Elements

Astatine Facts - Periodic Table of the Elements Atomic Number 85 Symbol At 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 302Â °C, an estimated boiling point of 337Â °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 Earths 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), Langes Handbook of Chemistry (1952), CRC Handbook of Chemistry Physics (18th Ed.) Â   Return to the Periodic Table