Astatine
Pronunciation/ˈæstətn, -tɪn/ (AS-tə-teen, -⁠tin)
Appearanceunknown, probably metallic
Mass number210 (most stable isotope)
Atomic number (Z)85
Groupgroup 17 (halogens)
Periodperiod 6
Blockp-block
Element category  Metalloid, sometimes classified as a nonmetal, or a metal
Electron configuration[Xe] 4f14 5d10 6s2 6p5
Electrons per shell
2, 8, 18, 32, 18, 7
Phase at STPsolid
Boiling point(At2) 503±3 K ​(230±3 °C, ​445±5 °F) (estimated)
Density (near r.t.)(At2) 6.35±0.15 g/cm3 (predicted)
Molar volume(At2) 32.94 cm3/mol (predicted)
Heat of vaporization(At2) 54.39 kJ/mol
Oxidation states−1, +1, +3, +5, +7
ElectronegativityPauling scale: 2.2
Ionization energies
  • 1st: 899.003 kJ/mol
Covalent radius150 pm
Van der Waals radius202 pm
Natural occurrencefrom decay
Thermal conductivity1.7 W/(m·K)
CAS Number7440-68-8
Namingafter Greek astatos (αστατος), meaning "unstable"
DiscoveryDale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)