Fermium
[Rn] 5f¹² 7s² · 2 · 8 · 18 · 32 · 30 · 8 · 2
The heaviest element that can be made by neutron capture in a reactor: beyond it the chain breaks, because every isotope past fermium fissions spontaneously too fast. Anything heavier has to be assembled atom by atom in an accelerator.
3D model
Bohr model: nucleus and electron shells from the real configuration. Valence electrons are highlighted.
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Atomic properties
- Atomic number
- 100
- Atomic mass
- 257 а.е.м. ≈
- Electron configuration
- [Rn] 5f¹² 7s²
- Electrons per shell
- 2 · 8 · 18 · 32 · 30 · 8 · 2
- Block
- f-block
- Group
- no data
- Period
- 7
- Electronegativity (Pauling)
- 1.3
- Electronegativity (Allen)
- 1.3
- Atomic radius
- 245 pm
- Covalent radius
- 167 pm
- Van der Waals radius
- 245 pm
- Ionisation energy 1
- 627 kJ/mol
- Electron affinity
- 33.96 kJ/mol
- Common oxidation states
- +3
- Oxidation states
- +2, +3
Physical properties
- State at 25 °C
- solid
- Density
- 9.7 g/cm³ ≈
- Melting point
- 1 800 K · 1 526.9 °C ≈
- Boiling point
- no data
- Speed of sound
- no data
Thermal properties
- Heat of fusion
- no data
- Heat of vaporisation
- no data
- Specific heat capacity
- no data
- Thermal conductivity
- no data
Mechanical properties
- Young's modulus
- no data
- Shear modulus
- no data
- Bulk modulus
- no data
- Poisson ratio
- no data
- Mohs hardness
- no data
- Brinell hardness
- no data
Electrical and magnetic properties
- Electrical resistivity
- no data
- Magnetic ordering
- paramagnetic
- Curie point
- no data
- Néel point
- no data
- Superconducting point
- no data
Crystal structure
- Crystal structure
- face-centred cubic (fcc) ≈
- Lattice constants
- no data
Abundance
- In the crust
- 0 mg/kg
- In the ocean
- 0 mg/L
- In the universe
- 0 mg/kg
- In the human body
- 0 mg/kg
Isotopes
| Isotope | Abundance | Half-life | Decay mode |
|---|---|---|---|
| 253Fm | — | 3 d | ЭЗ |
| 257Fm | — | 100.5 d | α |
Fermium-257, half-life 100.5 days, is the longest-lived. Beyond it lies the fermium gap: heavier isotopes fission spontaneously within milliseconds.
Discovery
- Year of discovery
- 1952
- Discovered by
- Albert Ghiorso and colleagues
- Where
- USA
- Origin of the name
- after Enrico Fermi
History
Fermium was found with einsteinium in the debris of the 1952 Ivy Mike test. The discovery was declassified in 1955 and the element named after Enrico Fermi.
Where it occurs
Absent from nature.
How it is produced
In high-flux reactors. It is made in picograms — never in weighable amounts.
Role in living things
No biological role.
Safety
Extremely radiotoxic; work proceeds on invisible quantities in hot cells.
Uses
Fundamental research only: the chemistry and nuclear properties of heavy actinides
Curiosities
- Fermium is the boundary between making elements in reactors and making them in accelerators.
- Nobody has ever seen fermium metal: its properties are known only from how single ions behave in solution.
- The fermium barrier is why superheavy elements are made by fusing nuclei rather than adding neutrons.
- Enrico Fermi built the world's first nuclear reactor, on a squash court under the stands at the University of Chicago.