as·ta·tine (ăstə-tēn′, -tĭn)
n. Symbol At
A highly unstable radioactive element, the heaviest of the halogen group, that resembles iodine in solution. Its longest lived isotope has a mass number of 210 and has a half-life of 8.3 hours. Atomic number 85; melting point 302°C; boiling point 337°C; valence probably 1, 3, 5, 7. See Periodic Table.
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