Atomic Properties of At
- Atomic Number of At
- 85
- Atomic Mass of At
- 210.0000 u
- Electron Configuration
- [Xe] 4f14 5d10 6s2 6p5
- Electronegativity
- 2.20
- Block
- p-block
- Group
- 17
- Period
- 6
Astatine occupies a real square on the periodic table but never forms a visible natural deposit. Tiny numbers of its atoms appear briefly in uranium and thorium decay chains, then disappear through further radioactive decay. Rarity here is not poor mining luck; it is the consequence of having no stable isotope.
Scientists first made and identified astatine in 1940 when Dale Corson, Kenneth MacKenzie, and Emilio Segrè bombarded bismuth with alpha particles at the University of California, Berkeley. They named it from astatos, Greek for unstable. Laboratory production still begins with nuclear reactions rather than chemical extraction.
Astatine belongs to group 17 beneath iodine, but its chemistry is difficult to map. Experiments involve tiny quantities, and relativistic effects may make its behavior less conventionally halogen-like than a simple downward trend suggests. Astatine-210 lasts only about eight hours. Astatine-211 has a similar clock and emits alpha particles, which travel only a short distance through tissue while depositing substantial energy. Researchers are investigating molecules that could carry At-211 selectively to cancer cells for targeted alpha therapy. This remains specialized medical research, not a routine commercial use.
The element cannot literally glow as a character illustration might suggest; there is far too little material to see, and radioactivity is not inherently visible. Its evidence comes from detectors and decay products.
Astatine is the Collection Agent found through absence: no stable isotope, no bulk sample, and no ordinary bottle. Yet a few measured atoms can test periodic trends and explore whether a short nuclear lifetime can be turned into a precisely delivered medical tool.