Astatine

Chemical element, symbol At and atomic number 85 / From Wikipedia, the free encyclopedia

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Astatine is a chemical element; it has symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours. Consequently, a solid sample of the element has never been seen, because any macroscopic specimen would be immediately vaporized by the heat of its radioactivity.

Quick facts: Astatine, Pronunciation, Appearance, Mass num...
Astatine, 85At
Astatine
Pronunciation/ˈæstətn, -tɪn/ (ASS-tə-teen, -tin)
Appearanceunknown, probably metallic
Mass number[210]
Astatine in the periodic table
 I 

At

Ts
poloniumastatineradon
Atomic number (Z)85
Groupgroup 17 (halogens)
Periodperiod 6
Block  p-block
Electron configuration[Xe] 4f14 5d10 6s2 6p5
Electrons per shell2, 8, 18, 32, 18, 7
Physical properties
Phase at STPsolid (predicted)
Density (near r.t.)8.91–8.95 g/cm3 (estimated)[1]
Molar volume23.6 cm3/mol (estimated)[1]
Atomic properties
Oxidation states−1, +1, +3, +5, +7[2]
Ionization energies
  • 1st: 899.003 kJ/mol[3]
Other properties
Natural occurrencefrom decay
Crystal structure face-centered cubic (fcc)
Face-centered cubic crystal structure for astatine

(predicted)[4]
CAS Number7440-68-8
History
Namingfrom Ancient Greek ἄστατος (ástatos) 'unstable'
DiscoveryDale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)
Isotopes of astatine
Main isotopes[5] Decay
abun­dance half-life (t1/2) mode pro­duct
209At synth 5.41 h β+ 209Po
α 205Bi
210At synth 8.1 h β+ 210Po
α 206Bi
211At synth 7.21 h ε 211Po
α 207Bi
Symbol_category_class.svg Category: Astatine
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The bulk properties of astatine are not known with certainty. Many of them have been estimated from its position on the periodic table as a heavier analog of fluorine, chlorine, bromine, and iodine, the four stable halogens. However, astatine also falls roughly along the dividing line between metals and nonmetals, and some metallic behavior has also been observed and predicted for it. Astatine is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal. Chemically, several anionic species of astatine are known and most of its compounds resemble those of iodine, but it also sometimes displays metallic characteristics and shows some similarities to silver.

The first synthesis of astatine was in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio G. Segrè at the University of California, Berkeley. They named it from the Ancient Greek ἄστατος (astatos) 'unstable'. Four isotopes of astatine were subsequently found to be naturally occurring, although much less than one gram is present at any given time in the Earth's crust. Neither the most stable isotope, astatine-210, nor the medically useful astatine-211 occur naturally; they are usually produced by bombarding bismuth-209 with alpha particles.

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