Actinides
Fermium
The heaviest element formed by neutron capture in reactors.
Atomic #100Mass[257]Blockf-blockPeriod7Group—
Fm100 · [257]
3D Atom Explorer
Inside the Fermium 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 Fermium atom step by step.
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Electron configuration
[Rn] 5f12 7s2
A neutral Fermium atom has 100 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 530 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
- 1800 K (1527 °C)
- Boiling point
- —
- Density
- —
- Electronegativity
- 1.3 Pauling
- Atomic radius
- —
- 1st ionization energy
- 627 kJ/mol
- Category
- Actinides
History
Discovery & naming
- Discovered
- 1952
- Discovered by
- Albert Ghiorso and colleagues
- Origin of name
- Physicist Enrico Fermi.
Notable uses
Scientific research only.
Cosmic origin
Where Fermium comes from
Human synthesis
Also first found in thermonuclear test debris. The heaviest element reachable by neutron capture alone.
Simplified origin map — many elements form through more than one astrophysical pathway.
Summary
- Atomic number
- 100
- Atomic mass
- [257]
- Category
- Actinides
- Group · Period
- — · 7
- Block
- f-block
- Shells
- 2 · 8 · 18 · 32 · 30 · 8 · 2