85
At
Astatine
210
Astatine (At)
HalogenGroup 17Period 6p-block-blockRadioactive
Astatine is a very rare radioactive chemical element with the chemical symbol At and atomic number 85. It occurs on Earth as the decay product of various heavier elements. All its isotopes are short-lived; the most stable is astatine-210, with a half-life of 8.1 hours.
Latin name: Astatinum
Atomic Number
85
Atomic Mass
210 g/mol
Phase (STP)
Solid (predicted)
Electron Config.
[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
General
SymbolAt
Atomic Number85
Atomic Mass210 g/mol
CategoryHalogen
Group17
Period6
Blockp-block
Electron Configuration[Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵
Valence Electrons7
Colourunknown (radioactive, rare)
Appearanceunknown, probably metallic
Physical Properties
Phase (STP)Solid (predicted)
Atomic Properties
Atomic Radius202 pm
Electronegativity2.2 Pauling
Ionization Energy890 kJ/mol
Oxidation States+1, +3, +5, -1
Ion ChargeAt-/At+
Nuclear & Hazards
RadioactiveYes
Half-lifevaries by isotope; longest-lived isotopes have half-lives on the order of hours (e.g., ~8.1 h)
Abundance
In Universe0.00000000001%
In Earth's Crust0.00000000001%
Discovery & History
Discovery Year1940
Discovered ByDale R. Corson, K.R. MacKenzie, Emilio Segrè
Country of DiscoveryUSA
Isotopes of Astatine
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| At-209 | — | 5.41 hours | α, EC |
| At-210 | — | 8.1 hours | α, EC |
| At-211 | — | 7.214 hours | α, EC |