Astatine
Pronunciation | /ˈ æ s t ə t iː n, -t ɪ n/ ​(AS-tə-teen, -⁠tin)
Appearance | unknown, probably metallic
Mass number | 210 (most stable isotope)
Atomic number (Z) | 85
Group | group 17 (halogens)
Period | period 6
Block | p-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 STP | solid
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
Electronegativity | Pauling scale: 2.2
Ionization energies | 1st: 899.003 kJ/mol
Covalent radius | 150 pm
Van der Waals radius | 202 pm
Natural occurrence | from decay
Thermal conductivity | 1.7 W/(m·K)
CAS Number | 7440-68-8
Naming | after Greek astatos (αστατος), meaning "unstable"
Discovery | Dale R. Corson, Kenneth Ross MacKenzie, Emilio Segrè (1940)