Astatine

85 polonium ← astatine → radon I ↑ At ↓ (Uus) periodic table
General
Name, Symbol, Number	astatine, At, 85
Chemical series	halogens
Group, Period, Block	17, 6, p
Appearance	metallic
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, ? °F)
Heat of vaporization	ca. 40 kJ/mol
Vapor pressure P/Pa 1 10 100 1 k 10 k 100 k at T/K 361 392 429 475 531 607
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
Main article: Isotopes of astatine iso NA half-life DM DE (MeV) DP 210At 100% 8.1 h Epsilon 3.981 210Po Alpha 5.631 206Bi
References

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 Segrè 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

Wikimedia Commons has media related to:

Astatine

• WebElements.com - Astatine