Quick Facts
| Property | Value |
|---|---|
| Symbol | At |
| Atomic Number | 85 |
| Atomic Mass | [210] u |
| Category | Halogen |
| Period | 6 |
| Group | 17 |
| Block | p |
| Electron Configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ |
Physical Properties
| Property | Value |
|---|---|
| State at 20°C | Solid (predicted) |
| Density | ~7 g/cm³ (estimated) |
| Melting Point | 302°C (575 K) (estimated) |
| Boiling Point | 337°C (610 K) (estimated) |
| Appearance | Unknown (probably dark) |
History and Discovery
Discovered by: Dale Corson, Kenneth MacKenzie, Emilio Segrè Year of Discovery: 1940 Location: University of California, Berkeley, USA
Etymology
From Greek "astatos" meaning "unstable."
Properties
- Rarest naturally occurring element
- Most radioactive naturally occurring element
- Never been seen in bulk
- Properties largely predicted, not measured
Applications and Uses
- Astatine-211 for targeted cancer therapy (research)
- No other practical applications due to extreme rarity
Interesting Facts
- Less than 30 grams exists in Earth's crust at any moment
- Rarest naturally occurring element
- No one has ever seen enough to know its color
- Half-life of At-210 is only 8.1 hours
- Most properties are theoretical estimates