Astatine

Astatine (210) −1   At 85 1s22s22p63s23p63d104s24p6 4d105s25p64f145d106s26p5 [ ? ] Halogen: Hazard: Radioactive

Astatine (Gr.: άστατος, unstable) is a chemical element, having the chemical symbol At. Its atomic number (the number of protons) is 85. It has a standard atomic weight of 210 g•mol ⁻¹ and is a solid in its elemental form. The total amount of astatine present in the earth's crust is less than 1 ounce (28 grams).

Astatine is considered a member of the "Halogen" class of elements. At a pressure of 101.325 kPa, it has a boiling point of ~340 °C and a melting point of 302 °C.

History

Astatine was first synthesized in 1940 by D.R. Corson, K.R. MacKenzie, and E. Segre at the University of California by bombarding bismuth with alpha particles. The longest-lived isotopes, with naturally occurring uranium and thorium isotopes, and traces of ²¹⁷At are equilibrium with ²³³U and ²³⁹Np resulting from integration of thorium and uranium with naturally produced neutrons.

Production

Astatine can be produced by bombarding bismuth with energetic alpha particles to obtain the relatively long-lived 209-211At, which can be distilled from the target by heating in air.

Chemistry

The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. Astatine is said to be more metallic than iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine.

Attribution

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