| Astatine - At
CAS: 7440-68-8 Description: Radioactive halogen, more metallic than iodine Classification: Halogen Date of Discovery: 1940 Discoverer: D.R. Corson Name Origin: Greek astatos, "unstable" |
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Atomic Number: 85
Number of Neutrons: 125 Atomic Mass: (210.0) amu Melting Point: 302 °C Boiling Point: 337 °C (est.) Density (293 K): Atomic volume: Electrical resistivity: Thermal conductivity: 0.500 W/cmK Enthalpy of atomization: 92 kJ/mol (est.) Enthalpy of vaporization: Enthalpy of fusion: Specific heat capacity: |
Energy levels: 2-8-18-32-18-7
Electron configuration: [Xe]4f155d106s26p5 Crystal Structure: Atomic radius: 1.43 Å Covalent radius: 1.45 Å Oxidation States: -1, +1, +3, +5, or +7 Electronegativity, Pauling: 1.96 Electron affinity: 2.8 eV First ionization energy: 9.5 eV 2nd ionization energy: 3rd ionization energy: Polarizability: 6.0 10-24cm3 |
| Isotope | Natural Abundance | Atomic Mass | Half-life | Decay Mode | Spin |
| 196At | 195.9957 | 0.3 s |  |
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| 197mAt | 4 s | |
(1/2+) | ||
| 197At | 196.9939 | 0.35 s |  +, EC; |
(9/2-) | |
| 198mAt | 1.5 s | +, EC; |
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| 198At | 197.9928 | 5 s | |
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| 199At | 198.9910 | 7.1 s | +, EC; |
9/2- | |
| 200mAt | 4.3 s | +, EC; |
10- | ||
| 200At | 199.990 | 43 s | +, EC; |
5+ | |
| 201At | 200.9885 | 1.48 s | +, EC; |
9/2- | |
| 202mAt |  1.5 s |
IT | |||
| 202At | 201.9885 | 3.02 m | +, EC; |
5+ | |
| 203At | 202.9868 | 7.4 m | +, EC; |
9/2- | |
| 204At | 203.9873 | 9.1 m | +, EC; |
(5+) | |
| 205At | 204.98604 | 26 m | +, EC; |
(9/2-) | |
| 206At | 205.98660 | 29.4 m | +, EC; |
5+ | |
| 207At | 206.98578 | 1.81 h | +, EC; |
9/2- | |
| 208At | 207.98657 | 1.63 h | +, EC; |
(6+) | |
| 209At | 208.98616 | 5.4 h | +, EC; |
(6+) | |
| 210At | 209.98713 | 8.1 h | EC; |
5+ | |
| 211At | 210.987481 | 7.21 h | EC; |
9/2- | |
| 212mAt | 0.119 s | |
(9-) | ||
| 212At | 211.990735 | 0.314 s | |
(1-) | |
| 213At | 212.992922 | 0.11 µs | |
9/2- | |
| 214mAt | 0.76 µs | |
(9-) | ||
| 214At | 213.996357 | 0.56 µs | |
(1-) | |
| 215At | 214.99864 | 0.10 ms | |
(9/2-) | |
| 216At | 216.002408 | 0.30 ms | |
(1-) | |
| 217At | 217.00471 | 32 ms | |
(9/2-) | |
| 218At | 218.00868 | 1.6 s | |
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| 219At | 219.0113 | 50 s | |
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| 220At | 220.0153 | 3.71 m | - |
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| 221At | 2.3 m | ||||
| 222At | 5.4 s | ||||
| 223At | 50 s | ||||
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Synthesized in 1940 by D. R. Corson, K. R. MacKenzie, and E. Segre at the University of California by bombarding bismuth with alpha particles. The longest-lived isotope, 210At, has a half-life of only 8.1 hours. Thirty-four isotopes and isomers are now known. Minute quantities of 215At, 218At, and 219At exist in equilibrium in nature with naturally occurring uranium and thorium isotopes, and traces of 217At are at equilibrium with 233U and 239Np resulting from interaction of thorium and uranium with naturally produced neutrons. The total amount of astatine present in the earth's crust, however, is less than 1 oz. Astatine can be produced by bombarding bismuth with energetic alpha particles to obtain the relatively long-lived 209-211At, which can be distilled from the target by heating it in air. Only about 0.05 µg of astatine has been prepared to date. The "time of flight" mass spectrometer has been used to confirm that this highly radioactive halogen behaves chemically very much like other halogens, particularly iodine. The interhalogen compounds AtI, AtBr, and AtCl are known to form, but it is not yet known if astatine forms diatomic astatine molecules. HAt and CH3At (methyl astatide) have been detected. Astatine is said to be more metallic that iodine, and, like iodine, it probably accumulates in the thyroid gland. Workers at the Brookhaven National Laboratory have recently used reactive scattering in crossed molecular beams to identify and measure elementary reactions involving astatine.
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Sources for the information on this website include: Lide, David R., ed. CRC Handbook of Chemistry and Physics, 78th Ed., 1997-1998. |
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