Astatine
Element 85 · Halogen
Astatine sits below iodine in the halogen group, but almost everything about it is inferred rather than measured: it decays too fast and exists in too tiny amounts to weigh or bottle. Chemists study it atom by atom as it forms and vanishes.
Its chemistry resembles iodine's, forming the -1 anion and higher oxidation states, and researchers are investigating astatine-211 for targeted alpha therapy against cancer — a promising medical use for one of nature's scarcest substances.
Key facts
| Atomic number | 85 |
|---|---|
| Atomic weight | [210] |
| Category | Halogen |
| Group / Period | 17 / 6 |
| Block | p |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p5 |
| Common oxidation states | -1, +1, +5 |
| State at STP | Solid |
| Electronegativity | 2.20 |
| Density | ~7 g/cm³ (estimated) |
| Melting point | 302 °C (estimated) |
| Boiling point | 337 °C (estimated) |
Occurrence
Astatine forms only as a fleeting decay product in uranium and thorium ores. Less than a gram exists naturally in Earth's crust at any moment.
Applications
Fundamental research only
At-211 targeted alpha therapy (experimental)
Common compounds
- hydrogen astatide
- sodium astatide
Less than a gram of astatine exists naturally in Earth's crust at any moment — chemists study it one atom at a time.
Data source: IUPAC standard atomic weights 2021