Astatine
metalloid · period 6 · group 17 (halogens) · p-block
Astatine is a chemical element with the symbol At and atomic number 85. It is the rarest naturally occurring element in the Earth's crust, occurring only as the decay product of various heavier elements.
What the numbers say
At standard temperature and pressure Astatine is a solid, sitting in period 6, group 17 of the p-block.
Its melting point of 575 K (302 °C) is the 80th highest of the 110 elements with a measured value — mid-range among the elements.
Pauling electronegativity is 2.2. Paired with oxygen (3.44) that is a difference of 1.24, which puts the bond polar covalent — oxides here tend to be semiconducting or refractory rather than salt-like.
It is reported in 5 oxidation states (-1, 1, 3, 5, 7), which sets how many distinct compounds and phases it can form.
First identified in 1940.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing At — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 18 · N 32 · O 18 · P 7
Properties
| Atomic number | 85 |
|---|---|
| Atomic mass | 210 u |
| Series | metalloid |
| Group | 17 |
| Period | 6 |
| Block | p-block |
| Phase at STP | Solid |
| Melting point | 575 K (302 °C) |
| Boiling point | 610 K (337 °C) |
| Electronegativity (Pauling) | 2.2 |
| Electron configuration | [Xe] 4f¹⁴ 5d¹⁰ 6s² 6p⁵ |
| Oxidation states | -1,1,3,5,7 |
| Discovered | 1940 |
← Back to the periodic table
See At in context with all 118 elements.
Working with astatine in a real design?
Ask the materials chat how At behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.