Astatine

Astatine, ₈₅At

Astatine
Pronunciation	/ˈæstətiːn, -tɪn/ ​(ASS-tə-teen, -⁠tin)
Appearance	unknown, probably metallic
Mass number	[210]
Astatine in the periodic table
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson  I  ↑ At ↓ Ts polonium ← astatine → radon
Atomic number (Z)	85
Group	group 17 (halogens)
Period	period 6
Block	p-block
Electron configuration	[Xe] 4f14 5d10 6s2 6p5
Electrons per shell	2, 8, 18, 32, 18, 7
Physical properties
Phase at STP	solid (predicted)
Density (near r.t.)	8.91–8.95 g/cm3 (estimated)[1]
Molar volume	23.6 cm3/mol (estimated)[1]
Atomic properties
Oxidation states	common: −1, +1 +3,[2] +5,[2] +7[2]
Ionization energies	1st: 899.003 kJ/mol[3]
Other properties
Natural occurrence	from decay
Crystal structure	​face-centered cubic (fcc) (predicted)[4]
CAS Number	7440-68-8
History
Naming	from Ancient Greek ἄστατος (ástatos) 'unstable'
Discovery	Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)
Isotopes of astatine v e
Main isotopes[5] Decay abun­dance half-life (t1/2) mode pro­duct 209At synth 5.41 h β+ 209Po α 205Bi 210At synth 8.1 h β+ 210Po α 206Bi 211At synth 7.21 h ε 211Po α 207Bi
Category: Astatine view talk edit | references

Astatine is a chemical element; it has 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 fluorine, chlorine, bromine, and iodine, the four stable halogens. 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.