Quick answerEinsteinium (Es) is an actinide with atomic number 99 and a mass number of 252 (the most stable isotope), in period 7. It was discovered by Albert Ghiorso and colleagues in 1952. It is used for synthesising heavier elements and actinide research. Its electron configuration is [Rn] 5f11 7s2.
Einsteinium was discovered in the debris of the first hydrogen bomb, and only milligrams have ever been made.
Key facts
| Symbol | Es |
|---|---|
| Atomic number | 99 |
| Atomic mass | [252] — mass number of the most stable isotope |
| Category | actinide |
| Group | — (f-block element, no group number) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 5f11 7s2 |
| Discovered | Albert Ghiorso and colleagues, 1952 |
| Uses | synthesising heavier elements, actinide research, nuclear forensics |
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Keep exploring
- Periodic table — all 118 elements
- Neptunium (Np) — another actinide, atomic number 93
- Plutonium (Pu) — another actinide, atomic number 94
- Americium (Am) — another actinide, atomic number 95
- Curium (Cm) — another actinide, atomic number 96
- Berkelium (Bk) — another actinide, atomic number 97
- Californium (Cf) — another actinide, atomic number 98
- Fermium (Fm) — another actinide, atomic number 100
- Mendelevium (Md) — another actinide, atomic number 101
- Nobelium (No) — another actinide, atomic number 102
- Lawrencium (Lr) — another actinide, atomic number 103
- All actinide elements — on the periodic table
Sources & last updated
- CIAAW — Standard Atomic Weights
- PubChem Periodic Table
- Wikipedia — Timeline of chemical element discoveries
Last updated: . Figures are shown with their year; where sources disagree, the value is left out rather than estimated.