polonium - astatine - radon I At Uus         Full table
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	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
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)
Most stable isotopes
iso NA half-life DM DE MeV DP 210At 100% 8.1 h Epsilon Alpha 3.981 5.631 210Po 206Bi
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 occurring 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

• Los Alamos National Laboratory - Astatine

External links

• WebElements.com - Astatine
• EnvironmentalChemistry.com - Astatine