Other Definitions
astatine (dict)
|
Astatine | colspan="2" cellspacing="0" cellpadding="2" | {| align="center" border="0" | | colspan="2" align="center" | polonium - astatine - radon | rowspan="3" valign="center" | I
At
Uus
| align="center" | Click for description
| } | | colspan="2" bgcolor="#ffff99" | General | | Name, Symbol, Number | Astatine, At, 85 | | Series | Halogens | | Group, Period, Block | 17 (VIIA), 6, p | | Density, Hardness | no data, no data | | Appearance | metallic | | colspan="2" bgcolor="#ffff99" | Atomic properties | | Atomic weight | 210 amu | | Atomic radius | no data | | Covalent radius | 127 pm | | van der Waals radius | no data | | Electron configuration | [Xe]4f14 5d10 6s2 6p5 | | e- 's per energy level | 2, 8, 18, 32, 18, 7 | | Oxidation states (Oxide) | 1,3,5,7 (unknown) | | Crystal structure | no data | | colspan="2" bgcolor="#ffff99" | Physical properties | | State of matter | solid | | Melting point | 575 K (576 F) | | Boiling point | 610 K (639 F) | | Molar volume | no data | | Heat of vaporization | no data | | Heat of fusion | 114 kJ/mol | | Vapor pressure | no data | | Speed of sound | no data | | colspan="2" bgcolor="#ffff99" | Miscellaneous | | Electronegativity | 2.2 (Pauling scale) | | Specific heat capacity | no data | | Electrical conductivity | no data | | Thermal conductivity | 1.7 W/(m*K) | | 1st ionization potential | 920 kJ/mol (estimated) | | colspan="2" bgcolor="#ffff99" | Most stable isotopes | | colspan="2" | {| border="1" cellspacing="0" cellpadding="2" width="100%" | | iso | NA | half-life | DM | DE MeV | DP | | 210At | 100% | 8.1 h | Epsilon
Alpha | 3.981
5.631 | 210Po
206Bi | } | | colspan="2" bgcolor="#ffff99" | SI units & STP are used except where noted. | Astatine is a chemical element in the periodic table that has the symbol At and atomic number 85. This radioactive element occurs naturally from uranium and thorium decay and is the heaviest of the halogens. Notable characteristics This highly radioactive element has been confirmed by mass spectrometers to behave chemically much like other halogens, especially iodine (it probably accumulates 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. With the possible exception of francium, astatine is the rarest naturally occuring element with the total amount in Earth's crust estimated to be less than 1 oz (28 g) at any one time; this amounts to less than one teaspoon of the element. History Astatine (Greek astatos meaning "unstable") was first synthesized in 1940 by Dale R. Corson, K. R. MacKenzie, and Emilio Segre of the University of California, Berkeley by barraging bismuth with alpha particles. An earlier name for the element was alabamine (Ab). Occurrence Astatine is produced by bombarding bismuth with energetic alpha particles to obtain relatively long-lived At-209 - At-211, which can then be distilled from the target by heating in the presence of air. Isotopes Astatine has 41 known isotopes, all of which are radioactive; the longest-lived isotope is 210At which has a half-life of 8.1 hours. The shortest-lived isotope is 213At which has a half-life of 125 nanoseconds. References External links
|
 |