|
General |
Name, Symbol, Number | Astatine, At, 85 |
Series | Halogens |
Group, Period, Block | 17 (VIIA), 6 , p |
Density, Hardness | no data, no data |
Appearance | metallic |
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 |
Physical Properties |
State of matter | solid |
Melting point | 575 K (576 °F) |
Boiling point | no data |
Molar volume | no data |
Heat of vaporization | no data |
Heat of fusion | 114 kJ/mol |
Vapor pressure | no data |
Speed of sound | no data |
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 | 20 kJ/mol |
Most Stable Isotopes |
|
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.
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.
The total amount of astatine in the earth's crust is estimated to be less than 1 oz (28 g) at any one time.
Astatine (
Greek astatos meaning "unstable") was first synthesized in
1940 by Dale Corson, K.R. MacKenzie, and Emilio Segre of the
University of California by barraging
bismuth with
alpha particles.
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.
Astatine has about 20 known
isotopes, all of which are
radioactive; the longest-lived isotope is
210At which has a
half-life of only 8.3 hours. Astatine is a
halogen and possibly accumulates in the
thyroid like
iodine.