Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements. All of astatine's isotopes are short-lived; the most stable is astatine-210, with a half-life of 8. 1 hours. Consequently, a solid sample of the element has never been seen, because any macroscopic specimen would be immediately vaporized by the heat of its radioactivity.

The bulk properties of astatine are not known with certainty. Many of them have been estimated from its position on the periodic table as a heavier analog of iodine, and a member of the halogens (the group of elements including fluorine, chlorine, bromine, iodine and tennessine). However, astatine also falls roughly along the dividing line between metals and nonmetals, and some metallic behavior has also been observed and predicted for it. Astatine is likely to have a dark or lustrous appearance and may be a semiconductor or possibly a metal. Chemically, several anionic species of astatine are known and most of its compounds resemble those of iodine, but it also sometimes displays metallic characteristics and shows some similarities to silver.

The first synthesis of astatine was in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio G. Segrè at the University of California, Berkeley. They named it from the Ancient Greek ἄστατος (astatos) 'unstable'. Four isotopes of astatine were subsequently found to be naturally occurring, although much less than one gram is present at any given time in the Earth's crust. Neither the most stable isotope, astatine-210, nor the medically useful astatine-211 occur naturally; they are usually produced by bombarding bismuth-209 with alpha particles.

© Wikipedia | CC-by-SA-3.0 | Read more …

Atomic properties

Atomic mass(209.987 u)

Atomic radii

Radius (calculated)127 pm

Atomic shell

Electron configurationXe 4f14 5d10 6s2 6p5
Ionization energy(1st) 9.31751 eV
(2nd) 17.88 eV
(3rd) 26.58 eV
(4th) 39.65 eV
(5th) 50.39 eV
(6th) 72 eV
(7th) 85.1 eV
Shell model

Physical properties

Density(6.4 g·cm−3)
Molar volume(3.3·10-5 m3·mol−1)


Melting enthalpy(6 kJ·mol-1)
Enthalpy of vaporization(40 kJ·mol-1)

Heat and conductivity

Thermal conductivity2 W·m-1·K-1



Chemical properties

Oxidation state±1, 3, 5, 7


Pauling scale2.2
Allred-Rochow scale1.9
Mulliken scale2.85
Nagle scale2.12

Other properties

Natural occurrenceDecay product
Crystal structureFace-centered cubic
Goldschmidt Classificationsynthetic
Superconductorwithout transition tempperature
Radioactivityhighly radioactive