Einsteinium (Es)
Actinide · Radioactive · Synthetic
Einsteinium was discovered in the debris of the first hydrogen bomb test in 1952 — its existence was a military secret for three years. Named for Albert Einstein, it has no uses beyond fundamental research.
Position on the periodic table
Atomic properties
| Atomic number | 99 |
|---|---|
| Atomic mass | 252 amu |
| Electron configuration | 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f11 |
| Noble gas shorthand | [Rn] 5f11 7s2 |
| Electrons per shell | 2, 8, 18, 32, 29, 8, 2 |
| Valence electrons (outer shell) | 2 |
| Common oxidation states | +3 |
| Electronegativity (Pauling) | 1.3 |
| Covalent radius (approx.) | Not available |
| First ionization energy | 619 kJ/mol |
| Electron affinity | -28.6 kJ/mol |
Physical properties
| State at 25 °C | Solid |
|---|---|
| Density | 8.84 g/cm³ |
| Melting point | 859.85 °C (1133 K) |
| Boiling point | 995.85 °C (1269 K) |
| Appearance | silver-colored |
| Radioactive | Yes |
| Origin | Synthetic (lab-made) |
Electron configuration of einsteinium
Einsteinium's ground-state electron configuration is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f11, usually shortened to [Rn] 5f11 7s2. Its electrons occupy 7 shells (2, 8, 18, 32, 29, 8, 2), placing it in period 7 of the f-block. Explore it interactively in the electron configuration calculator.
Uses of einsteinium
- Fundamental research on heavy-element chemistry
Biological role: None.
Occurrence: Entirely synthetic; made in the highest-flux reactors.
History and discovery
Discovered: 1952 — Lawrence Berkeley National Laboratory. Name origin: Named after Albert Einstein.
Identified by Albert Ghiorso's team in fallout from the first thermonuclear explosion, November 1952.
Safety notes
Intensely radioactive; available only in sub-milligram research quantities.
Educational context only — always follow your school's laboratory rules and never handle chemicals without proper supervision. See our disclaimer.
Practice questions
Quick practice: Einsteinium
1. What is the chemical symbol of Einsteinium?
2. What is the atomic number of Einsteinium?
3. Which category does Einsteinium belong to?
4. What is the state of Einsteinium at room temperature?
5. Which period of the periodic table is Einsteinium in?
Einsteinium FAQs
What is the atomic number of einsteinium?
Einsteinium's atomic number is 99 — every einsteinium atom has 99 protons in its nucleus.
What is the symbol for einsteinium?
Es. Named after Albert Einstein.
Is einsteinium a metal, nonmetal, or metalloid?
Einsteinium is classified as a actinide.
What state is einsteinium at room temperature?
At about 25 °C, einsteinium is a solid. It melts at 859.85 °C.
What is einsteinium used for?
Key uses include: fundamental research on heavy-element chemistry.
Related elements
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