Es
Einsteinium
Einsteinium is a chemical element with the symbol Es and atomic number 99. It has a mass number of 252, sits in period 7 of the f-block, and is classified as an actinide.
Properties
| Symbol | Es |
|---|---|
| Atomic number | 99 |
| Mass number | 252 |
| Category | Actinide |
| Group | f-block — no group |
| Period | 7 |
| Electron configuration | [Rn] 5f11 7s2 |
| Outer-shell electrons | 2 |
The figure of 252 is a mass number rather than a measured atomic weight, because this element has no stable isotope.
Calculate with einsteinium
- Molar mass of any formula containing it
- Electron configuration, including ions
- Effective nuclear charge by Slater's rules
- Average atomic mass from isotope abundances
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.