Difference between revisions of "Astatine" - New World Encyclopedia
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== History == | == History == | ||
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+ | The name astatine was derived from the [[Greek language|Greek]] word αστατος (''astatos''), meaning "unsteady". Well before it was discovered, [[Dmitri Mendeleev]] had predicted its existence based on his analysis of the [[periodic table]]. He called it "eka-iodine". | ||
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+ | This element was discovered in 1940 by [[Dale R. Corson]]*, [[K. R. MacKenzie]]*, and [[Emilio Segrè]]* at the [[University of California, Berkeley]]*. They barraged [[bismuth]] with [[alpha particle]]s. An earlier name for the element was ''alabamine'' (Ab). | ||
== Notable characteristics == | == Notable characteristics == |
Revision as of 02:46, 11 December 2006
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General | ||||||||||||||||
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Name, Symbol, Number | astatine, At, 85 | |||||||||||||||
Chemical series | halogens | |||||||||||||||
Group, Period, Block | 17, 6, p | |||||||||||||||
Appearance | metallic (presumed) | |||||||||||||||
Atomic mass | (210) g/mol | |||||||||||||||
Electron configuration | [Xe] 4f14 5d10 6s2 6p5 | |||||||||||||||
Electrons per shell | 2, 8, 18, 32, 18, 7 | |||||||||||||||
Physical properties | ||||||||||||||||
Phase | solid | |||||||||||||||
Melting point | 575 K (302 °C, 576 °F) | |||||||||||||||
Boiling point | ? 610 K (? 337 °C, ? 639 °F) | |||||||||||||||
Heat of vaporization | ca. 40 kJ/mol | |||||||||||||||
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Atomic properties | ||||||||||||||||
Crystal structure | no data | |||||||||||||||
Oxidation states | ±1, 3, 5, 7 | |||||||||||||||
Electronegativity | 2.2 (Pauling scale) | |||||||||||||||
Ionization energies | 1st: (est.) 920 kJ/mol | |||||||||||||||
Miscellaneous | ||||||||||||||||
Magnetic ordering | no data | |||||||||||||||
Thermal conductivity | (300 K) 1.7 W/(m·K) | |||||||||||||||
CAS registry number | 7440-68-8 | |||||||||||||||
Notable isotopes | ||||||||||||||||
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Astatine (chemical symbol At, atomic number 85) is a radioactive element that occurs naturally from uranium-235 and uranium-238 decay. It is the heaviest of the halogens.
Occurrence and production
The total amount of astatine in the Earth's crust has been estimated to be only about one ounce. It is produced in nature by the radioactive decay of uranium and thorium, and it is therefore present in trace amounts in minerals of these elements.
Astatine can be artificially produced by bombarding bismuth with energetic alpha particles. This method generates the relatively long-lived isotopes 209At, 210At, and 211At. These isotopes can then be separated from the bismuth by a process of distillation, which involves heating the mixture in the presence of air, and condensing the vapors in a separate container.
History
The name astatine was derived from the Greek word αστατος (astatos), meaning "unsteady". Well before it was discovered, Dmitri Mendeleev had predicted its existence based on his analysis of the periodic table. He called it "eka-iodine".
This element was discovered in 1940 by Dale R. Corson, K. R. MacKenzie, and Emilio Segrè at the University of California, Berkeley. They barraged bismuth with alpha particles. An earlier name for the element was alabamine (Ab).
Notable characteristics
This highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens, especially iodine (it would probably accumulate in the thyroid gland like iodine). Astatine is thought to be more metallic than iodine. Researchers at the Brookhaven National Laboratory have performed experiments that have identified and measured elementary reactions that involve astatine; however, chemical research into astatine is limited by its extreme rarity, which is a result of its extremely short half-life.
Astatine is the rarest naturally-occurring element, with the total amount in Earth's crust estimated to be less than 1 oz (28 g) at any given time; this amounts to less than one teaspoon of the element. The Guinness Book of Records has dubbed the element the rarest on Earth, stating: "Only around 0.9 oz (25 g) of the element astatine (At) occurring naturally"; Isaac Asimov wrote a 1955 essay on large numbers, scientific notation, and the size of the atom, in which he stated that the number of astatine atoms on Earth at any time was "only a trillion".
Isotopes
Astatine has many known isotopes, all of which are radioactive. Their mass numbers range from 191 to 223. There exist also 23 metastable excited states. Among the various known isotopes, the longest-lived member is 210At, which has a half-life of 8.1 hours; the shortest-lived member is 213At, which has a half-life of 125 nanoseconds.
Compounds
Multiple compounds of astatine have been synthesized in microscopic amounts and studied as intensively as possible before their inevitable radioactive disintegration. These compounds are primarily of theoretical interest; however, they are also being studied for potential use in nuclear medicine.
See also
ReferencesISBN links support NWE through referral fees
- Astatine Los Alamos National Laboratory. Accessed on December 10, 2006.
- Greenwood, N.N.; and Earnshaw, A. (1998). Chemistry of the Elements (2nd Edition). Oxford, U.K.; Burlington, Massachusetts: Butterworth-Heinemann, Elsevier Science. ISBN 0750633654. Online version available at [1]. Accessed on November 5, 2006.
- Cotton, F. Albert; and Wilkinson, Geoffrey (1980), Advanced Inorganic Chemistry (4th ed.), New York: Wiley. ISBN 0-471-02775-8.
- Chang, Raymond (2006). Chemistry (ninth ed.) New York: McGraw-Hill Science/Engineering/Math. ISBN 0073221031.
External links
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