Astatine
Definition and meaning of Astatine in chemistry.
![Astatine element card: symbol At, atomic number 85, atomic mass [210], electron configuration [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵, oxidation states +1 -1, Halogen, group 17, period 6, solid at room temperature.](/assets/images/terms/astatine-chemical-element.webp)
Astatine is a highly radioactive and extremely rare halogen located on the periodic table. It is identified by the chemical symbol At and the designated atomic number 85. It is the heaviest known halogen and only exists briefly during natural radioactive decay.
In more detail
A heavier element breaks down and temporarily forms astatine before rapidly decaying even further. Astatine belongs to group 17 of the periodic table, located vertically directly below iodine. It currently holds the title as the rarest naturally occurring chemical element on Earth.
Scientists estimate that less than one single gram of astatine exists in the entire crust. This extreme scarcity is due to its very short half-life and incredibly rapid radioactive decay. Half-life is simply the time required for half of a radioactive sample to break down.
Astatine behaves chemically much like other typical halogens found in its designated periodic group. However, it exhibits noticeably more metallic properties than lighter halogens like stable solid iodine. It can readily form strong ionic bonds with various other nonmetal chemical elements during reactions.
All of its discovered isotopes are highly unstable and they decay very quickly into lighter elements. An isotope is a version of an element with a different number of atomic neutrons. Astatine-210 has the longest known half-life of all isotopes, lasting for a mere 8.1 hours.
Because of this instability, macroscopic or visible quantities have never been successfully assembled by humans. As a result, its physical properties are entirely deduced from advanced theoretical computer models. Scientists also predict its appearance and melting point using 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 |
Astatine-211 is actively researched in modern nuclear medicine for targeted alpha-particle cancer therapy in patients. This advanced medical therapy aims to selectively destroy malignant cancer cells inside the human body. It delivers destructive radiation directly to tumors without severely damaging the surrounding healthy biological tissue.
Frequently asked questions
Can a human being actually see a physical sample of solid astatine?
No macroscopic sample of astatine has ever been successfully viewed by the human eye. The intense, concentrated radiation from a visible amount would immediately generate extreme heat. This massive heat would instantly vaporize the radioactive sample and its immediate surroundings.
How is astatine reliably obtained for use in modern medical research?
Scientists successfully produce astatine synthetically while working inside advanced particle accelerator facilities. They intentionally bombard bismuth-209 target atoms with high-energy alpha particles to create it. This nuclear reaction successfully forces the lighter bismuth atoms to transform into heavier astatine.
Related terms
Sources & references
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