At
Astatine
Astatine is a chemical element with the symbol At and atomic number 85. It has a mass number of 210, sits in period 6 and group 17, and is classified as a halogen.
Properties
| Symbol | At |
|---|---|
| Atomic number | 85 |
| Mass number | 210 |
| Category | Halogen |
| Group | 17 |
| Period | 6 |
| Electron configuration | [Xe] 4f14 5d10 6s2 6p5 |
| Outer-shell electrons | 7 |
The figure of 210 is a mass number rather than a measured atomic weight, because this element has no stable isotope.
Calculate with astatine
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
Group 17
Atomic weights are the IUPAC 2021 standard values, abridged to the conventional five significant figures. Group, period, category and electron configuration are derived from the atomic number rather than stored, so they cannot drift out of step with it.