Periodic Table of the Elements Astatine

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Astatine


melting point: 302°C
boiling point: 337°C
density: unknown
most common ions: At, AtO, AtO3

Astatine is a radioactive halogen (the heaviest of the halogen elements) and is a solid at room temperature. Dale R. Carson, K. R. MacKenzie, and Emilio Segrè of the University of California produced the element in 1940 by bombarding an isotope of bismuth (209Bi) with alpha particles. The origin of the name "astatine" is the Greek word astatos, which means "unstable."

Astatine is found in only vanishingly small amounts in natureit is believed that only 30 grams (1 ounce) of the element are present in Earth's crust at any one time. It is produced naturally when the elements uranium and thorium decay. Astatine can also be produced in a nuclear reactor by the method used by its discoverers, according to the following reaction:

209 83Bi + 42 He 211 85At + 2 10n

The most stable isotope of astatine is 210At, which has a half-life of 8.1 hours. Other isotopes have mass numbers ranging from 193 to 223 and half-lives ranging from 125 nanoseconds (213At) to 7.2 hours (211At). Astatine is known to form interhalogen compounds with bromine (AtBr), chlorine (AtCl), and iodine (AtI). Additional compounds (HAt and CH3At) have also been detected.

Because of its scarcity and short half-life, there were no commercial uses for astatine as of 2003. Researchers are investigating astatine as a means of treating various cancers (e.g., lethal brain tumors) and diseases. Because of its similarities to iodine, which accumulates in the thyroid, it is believed that the element could be utilized to treat certain thyroid diseases.

see also Halogens; Radioactivity.

Stephanie Dionne Sherk

Bibliography

Lide, David R., ed. (2003). The CRC Handbook of Chemistry and Physics, 84th edition. Boca Raton, FL: CRC Press.

Internet Resources

Gagnon, Steve. "It's Elemental: Astatine." Jefferson Lab. Available from <http://education.jlab.org/itselemental/iso085.html>.

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astatine (ăs´tətēn,–tĬn) [Gr.,=unstable], semimetallic radioactive chemical element; symbol At; at. no. 85; at. wt. of most stable isotope 210; m.p. 302°C (estimated); b.p. 337°C (estimated); density unknown; valence believed to be +1, +3, +5, or +7. Astatine is the heaviest known halogen (Group 17 of the periodic table). Its chemical properties are believed to be similar to those of iodine. The most stable isotope, astatine-210, has a half-life of about 8 hours. More than 30 isotopes of astatine have been identified. Small amounts of astatine exist in equilibrium with uranium and thorium in the earth's crust, but the total amount of astatine is probably less than 1 oz. Astatine-211 (half-life 7.21 hr) is sometimes used as a radioactive tracer; like iodine, it collects in the thyroid gland. The discovery of astatine (first called alabamine) was announced in 1931 by Fred Allison and E. J. Murphy. In 1940, Emilio Segré, D. R. Corson, and K. R. Mackenzie produced astatine-211 by bombarding bismuth-209 with alpha particles in the cyclotron at the Univ. of California.

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astatine (symbol At) Semimetallic radioactive element that is one of the halogens (group VII of the periodic table). It is rare in nature, and is found in radioactive decay. At211 will collect in the thyroid gland and is used in medicine as a radioactive tracer. Properties: at.no. 85; r.a.m. 211; m.p. 302°C (575.6°F); b.p. 377°C (710.6°F); most stable isotope At210 (half-life 8.3hr).

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Periodic Table of the Elements: Astatine

Periodic Table of the Elements: Astatine
Atomic Number: 85
Atomic Symbol: At
  Astatine
Atomic Weight: (210)
Electron Configuration: 2 · 8 · 18 32 · 18 · 7

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as·ta·tine / ˈastəˌtēn; -tin/ • n. the chemical element of atomic number 85, a radioactive member of the halogen group. (Symbol: At)