Actinides
Einsteinium
A synthetic element first found in hydrogen bomb debris.
Atomic #99Mass[252]Blockf-blockPeriod7Group—
Es99 · [252]
3D Atom Explorer
Inside the Einsteinium atom
Switch between Bohr and Quantum Cloud modes to compare a simple teaching model with a more realistic probability-based view, and follow the guided tour to explore the Einsteinium atom step by step.
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Electron configuration
[Rn] 5f11 7s2
A neutral Einsteinium atom has 99 electrons (equal to its proton count). Choosing a different isotope above changes only the neutron count.
Shell distribution
Shell 12 e⁻Shell 28 e⁻Shell 318 e⁻Shell 432 e⁻Shell 529 e⁻Shell 68 e⁻Shell 72 e⁻
Electrons fill inner shells before outer ones; the outermost (valence) shell drives the element's chemistry.
Properties
Physical & atomic properties
- State (room temp)
- Solid
- Melting point
- 1133 K (860 °C)
- Boiling point
- 1269 K (996 °C)
- Density
- 8.84 g/cm³
- Electronegativity
- 1.3 Pauling
- Atomic radius
- —
- 1st ionization energy
- 619 kJ/mol
- Category
- Actinides
History
Discovery & naming
- Discovered
- 1952
- Discovered by
- Albert Ghiorso and colleagues
- Origin of name
- Physicist Albert Einstein.
Notable uses
Scientific research only.
Cosmic origin
Where Einsteinium comes from
Human synthesis
First identified in the debris of a 1952 thermonuclear test. Now made in reactors.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 99
- Atomic mass
- [252]
- Category
- Actinides
- Group · Period
- — · 7
- Block
- f-block
- Shells
- 2 · 8 · 18 · 32 · 29 · 8 · 2