Astatine (At)
Halogen · p-block · period 6 · group 17
Never seen — any visible piece would instantly vaporise from its own radioactive heat.
Astatine (symbol At) is chemical element number 85, a halogen in group 17, period 6 of the periodic table. Its standard atomic weight is (210) and its electron configuration is [Xe] 4f14 5d10 6s2 6p5. At room temperature it is a solid, and it is radioactive. The rarest naturally occurring element on Earth — less than a teaspoon exists in the whole crust at any moment.
Properties
| Atomic number | 85 |
|---|---|
| Atomic mass | (210) |
| Category | Halogen |
| Block | p-block |
| Group · Period | 17 · 6 |
| Electron configuration | [Xe] 4f14 5d10 6s2 6p5 |
| Electrons per shell | 2, 8, 18, 32, 18, 7 |
| State at 25 °C | solid |
| Melting point | 575 K |
| Boiling point | 610 K |
| Density | — |
| Electronegativity (Pauling) | 2.2 |
| Radioactive | Yes — no stable isotope |
| Origin | decay |
| Discovered | 1940 · Corson, MacKenzie & Segrè |
Key facts about Astatine
- The rarest naturally occurring element on Earth — less than a teaspoon exists in the whole crust at any moment.
- Its name is Greek for 'unstable'.
- The heaviest of the halogens; it behaves partly like a metal.
- Astatine-211 is being tested as a precise, short-range cancer treatment.
What Astatine is used for
Experimental targeted alpha-particle cancer therapy (research only).
Where it sits in the periodic table
Astatine is in group 17, period 6, of the p-block. Its electron configuration [Xe] 4f14 5d10 6s2 6p5 means its outermost shell holds 7 electrons, which is what places it here and explains much of its chemistry. See Astatine on the interactive table →
Astatine — frequently asked questions
What is Astatine used for?
Experimental targeted alpha-particle cancer therapy (research only).
Is Astatine radioactive?
Yes. Astatine has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Astatine?
Astatine has the electron configuration [Xe] 4f14 5d10 6s2 6p5, which is 2, 8, 18, 32, 18, 7 electrons per shell.
What group and period is Astatine in?
Astatine is in group 17, period 6, in the p-block. Its outer shell holds 7 electrons.
Who discovered Astatine?
Astatine was discovered in 1940 by Corson, MacKenzie & Segrè.