Astatine
Definition and meaning of Astatine in chemistry.
Astatine is a highly radioactive and extremely rare halogen with the chemical symbol At and atomic number 85. It is the heaviest known halogen and occurs naturally only as a fleeting, temporary intermediate step in the decay chains of heavier radioactive elements.
In more detail
Astatine belongs to group 17 of the periodic table, located vertically below iodine, and it currently holds the title as the rarest naturally occurring element in the Earth's crust. It is estimated that less than one single gram of astatine exists in the entire crust at any given moment due to its very short half-life and rapid radioactive decay. Astatine behaves chemically much like other typical halogens, although it exhibits noticeably more metallic properties than iodine and can readily form ionic bonds with other nonmetals. All of its discovered isotopes are highly unstable, with astatine-210 having the longest known half-life at just 8.1 hours. Because macroscopic, visible quantities have never been successfully assembled, its physical properties, such as its appearance and melting point, are entirely deduced from theoretical models and the periodic trends of lighter halogens.
Key facts
| Field | General Chemistry |
|---|---|
| Symbol | At |
| Atomic number | 85 |
| Atomic mass | [210] u |
| Category | Halogen |
| State at room temperature | Solid (predicted) |
| Longest-lived isotope | Astatine-210 (half-life 8.1 hours) |
| Year discovered | 1940 |
| Discoverers | Dale R. Corson, Kenneth Ross MacKenzie, and Emilio Segrè |
Astatine-211 is actively researched in modern nuclear medicine for targeted alpha-particle therapy to selectively destroy malignant cancer cells without severely damaging the surrounding healthy biological tissue.
Frequently asked questions
Can a human being actually see astatine?
No macroscopic sample of astatine has ever been viewed, because the intense, concentrated radiation from a visible amount would immediately generate enough heat to vaporize the sample and its surroundings.
How is astatine obtained for medical research?
Astatine is produced synthetically in advanced particle accelerators by intentionally bombarding bismuth-209 target atoms with high-energy alpha particles.