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Atomic Number: 85
Atomic Symbol: At
Atomic Weight: 210
Melting Point: 575.6 F (302 C)
Boiling Point: 644 F (340 C)
Word origin: The word astatine comes from the Greek word astatos, which means unstable.
Discovery: Astatine was synthesized in 1940 by a group of scientists at the University of California. D.R. Corson, K.R. MacKenzie, and E. Segre bombarded bismuth with alpha particles to get synthesized astatine.
Properties of astatine
Astatine is the rarest element on Earth. It is a highly radioactive halogen. Chemically, it behaves similarly to other halogens. The “time of flight” mass spectrometer was used to confirm astatine’s halogenic behavior. Astatine is especially similar in behavior to iodine, though astatine is more metallic. Like iodine, astatine is suspected to accumulate in the human thyroid gland. [See Periodic Table of the Elements]
Sources of astatine
Astatine occurs naturally; however, scientists estimate much less than an ounce in total exists worldwide. To produce astatine, bismuth is bombarded by energetic alpha particles. This results in the relatively long-lived 209-211At, which is then distilled from the target by heating in the air.
Small amounts of astatine isotope 217Atoccur naturally with uranium and thorium isotopes, which are found in the earth’s crust.
Isotopes of astatine
Astatine has the longest living isotopes. Along with traces of 217At, they exist in equilibrium with 233U and 239Np. This equilibrium is the result of integration of thorium and uranium with naturally produced neutrons.
(Source: Los Alamos National Laboratory)