100
Fm
Fermium
257
Fermium (Fm)
ActinidePeriod 7f-block-blockRadioactive
Fermium is a synthetic element with symbol Fm and atomic number 100. It is a member of the actinide series. It is the heaviest element that can be formed by neutron bombardment of lighter elements, and hence the last element that can be prepared in macroscopic quantities, although pure fermium metal has not yet been prepared.
Latin name: Fermium
Atomic Number
100
Atomic Mass
257 g/mol
Phase (STP)
Solid
Electron Config.
[Rn] 5f¹² 7s²
General
SymbolFm
Atomic Number100
Atomic Mass257 g/mol
CategoryActinide
Period7
Blockf-block
Electron Configuration[Rn] 5f¹² 7s²
Valence Electrons14
Coloursilvery (radioactive)
Physical Properties
Phase (STP)Solid
Atomic Properties
Atomic Radius245 pm
Electronegativity1.3 Pauling
Ionization Energy627 kJ/mol
Oxidation States+2, +3
Ion ChargeFm2+/Fm3+
Nuclear & Hazards
RadioactiveYes
Half-life100.5 days (Fm-257)
Abundance
In Earth's Crust0.000000000000001%
Discovery & History
Discovery Year1952
Discovered ByAlbert Ghiorso and co-workers
Country of DiscoveryUSA
Isotopes of Fermium
| Isotope | Abundance | Half-life | Decay |
|---|---|---|---|
| Fm-252 | — | 25.39 hours | α |
| Fm-255 | — | 20.07 hours | α |
| Fm-257 | — | 100.5 days | α |