astatine

American  

[as-tuh-teen, -tin] / ˈæs təˌtin, -tɪn /

noun

Chemistry.

1. a rare element of the halogen family. At; 85.

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astatine British  

/ -tɪn, ˈæstəˌtiːn /

noun

1. a radioactive element of the halogen series: a decay product of uranium and thorium that occurs naturally in minute amounts and is artificially produced by bombarding bismuth with alpha particles. Symbol: At; atomic no: 85; half-life of most stable isotope, ²¹⁰ At: 8.1 hours; probable valency: 1,3,5, or 7; melting pt: 302°C; boiling pt: 337°C (est)

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astatine Scientific  

/ ăs′tə-tēn′ /

1. A highly unstable, rare, radioactive element that is the heaviest of the halogen elements. Its most stable isotope 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.

2. See Periodic Table

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Etymology

Origin of astatine

1945–50; < Greek ástat ( os ) not steadfast, unstable ( see astatic) + -ine ²

Example Sentences

Astatine is the rarest naturally occurring element on Earth and among the least explored in the periodic table.

From Science Daily • Nov. 11, 2025

General Aspects of Astatine Element 85 has the dubious distinction of being one of very few solid elements that has never been obtained in any amount large enough to be visible to the naked eye.

From Scientific American • Jul. 5, 2013

Astatine was first made at Berkeley by bombarding bismuth with alpha particles, which produced astatine and released two neutrons.

From A Brief History of Element Discovery, Synthesis, and Analysis by Watson, Glen W.