Atomic Number

85

Symbol

At

Atomic Weight

(210)

Discovery

Corson et al 1940

Electron Configuration

[Xe]6s²4f¹⁴5d¹⁰6p⁵

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 Serge 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 uranium with neutrons. The total amount of astatine present in the Earth's crust is less than 1 ounce.