99Es[252]
Einsteinium (Es)
Element 99 · Actinide
Einsteinium (Es) is a chemical element with atomic number 99. It is classified as an actinide in period 7 of the periodic table (the f-block). Its most stable known isotope has mass number 252 and its ground-state electron configuration is [Rn] 5f¹¹ 7s².
Einsteinium facts
| Atomic number (Z) | 99 |
|---|---|
| Symbol | Es |
| Mass number of most stable isotope | [252] |
| Category | Actinide |
| Group | — (f-block) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 5f¹¹ 7s² |
| Electronegativity (Pauling) | 1.3 |
| State at 20 °C | Solid |
| Protons / electrons | 99 / 99 |
| Neutrons (most common isotope, approx.) | 153 |
| Molar mass | 252 g/mol |