Fermium
Element 100 · Actinide
Fermium is the heaviest element producible by successive neutron capture, found alongside einsteinium in hydrogen-bomb debris. Only tiny quantities have ever been made, and its longest-lived isotope decays with a half-life of about 100 days. Because so little exists, its chemistry is known only from tracer experiments showing it behaves like a typical late actinide with a stable +3 state. Properties are otherwise predicted, with limited experimental data. Every fermium isotope is radioactive, with half-lives measured in days.
Key facts
| Atomic number | 100 |
|---|---|
| Atomic weight | [257] |
| Category | Actinide |
| Group / Period | — / 7 |
| Block | f |
| Electron configuration | [Rn] 5f12 7s2 |
| Common oxidation states | +3 |
| State at STP | Solid |
| Electronegativity | 1.3 |
| Melting point | 1527 °C (estimated) |
Occurrence
Fermium is entirely synthetic, produced in high-flux reactors and once in thermonuclear tests. No weighable sample has ever been collected.
Applications
Fundamental research on the limits of neutron-capture synthesis
Tracer studies of late-actinide chemistry
No commercial applications
Common compounds
- Fermium(III) chloride (FmCl3, tracer scale)
- Fermium(III) oxide (Fm2O3, predicted)
Fermium was discovered in 1952 in the same H-bomb debris as einsteinium and named for physicist Enrico Fermi, a pioneer of nuclear reactors.
Data source: IUPAC standard atomic weights 2021