Fermium
actinide · period 7 · group 3 · f-block
Fermium is a synthetic element with the symbol Fm and atomic number 100. It is an actinide and 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.
What the numbers say
At standard temperature and pressure Fermium is a solid, sitting in period 7, group 3 of the f-block.
Its melting point of 1800 K (1527 °C) is the 29th highest of the 110 elements with a measured value — mid-range among the elements.
Pauling electronegativity is 1.3. Paired with oxygen (3.44) that is a difference of 2.14, which puts the bond predominantly ionic — expect a stable oxide ceramic.
It is reported in 2 oxidation states (2, 3), which sets how many distinct compounds and phases it can form.
First identified in 1952.
Check it against computed structures
The structure search queries the Materials Project, OQMD and the Open Materials Database for computed crystal structures containing Fm — with DFT formation energy, hull stability and band gap where the provider publishes them.
K 2 · L 8 · M 18 · N 32 · O 30 · P 8 · Q 2
Properties
| Atomic number | 100 |
|---|---|
| Atomic mass | 257 u |
| Series | actinide |
| Group | 3 |
| Period | 7 |
| Block | f-block |
| Phase at STP | Solid |
| Melting point | 1800 K (1527 °C) |
| Electronegativity (Pauling) | 1.3 |
| Electron configuration | [Rn] 5f¹² 7s² |
| Oxidation states | 2,3 |
| Discovered | 1952 |
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See Fm in context with all 118 elements.
Working with fermium in a real design?
Ask the materials chat how Fm behaves in your alloy system, what it does to weldability, and which grades to look at — with the source of every number named.