Einsteinium (symbol Es, atomic number 99) is a synthetic actinide first found in the debris of a hydrogen-bomb test. It is classified as a actinide and sits in the actinide series (f-block), period 7 of the periodic table.
Overview
Einsteinium is the chemical element with atomic number 99 and the symbol Es. With a standard atomic weight of [252], it is a actinide. In the periodic table it occupies the actinide series (f-block) and period 7, and under standard conditions it is normally a solid. Einsteinium is a synthetic actinide first found in the debris of a hydrogen-bomb test.
Atomic structure
An atom of Einsteinium has 99 protons in its nucleus and, when neutral, 99 electrons arranged in the configuration [Rn] 5f11 7s2. Einsteinium has no stable isotope; the value [252] refers to the mass number of its most stable or most commonly produced isotope.
Discovery and place in the table
Einsteinium was discovered in 1952 by Lawrence Berkeley National Laboratory. It follows Californium (Cf) and precedes Fermium (Fm) in order of atomic number.
| Atomic number | 99 |
|---|---|
| Symbol | Es |
| Atomic mass | [252] |
| Category | Actinide |
| Group | — |
| Period | 7 |
| Electron configuration | [Rn] 5f11 7s2 |
| Phase at STP | Solid |
| Discovered | 1952 (Lawrence Berkeley National Laboratory) |