Fermium (Fm)
Actinide · f-block · period 7
Never produced in visible amounts; properties known only for single atoms.
Fermium (symbol Fm) is chemical element number 100, a actinide in the actinide series (f-block), period 7 of the periodic table. Its standard atomic weight is (257) and its electron configuration is [Rn] 5f12 7s2. Its state at room temperature is unknown, and it is radioactive. Also first found in hydrogen-bomb debris; named after Enrico Fermi.
Properties
| Atomic number | 100 |
|---|---|
| Atomic mass | (257) |
| Category | Actinide |
| Block | f-block |
| Group · Period | f-block series · 7 |
| Electron configuration | [Rn] 5f12 7s2 |
| Electrons per shell | 2, 8, 18, 32, 30, 8, 2 |
| State at 25 °C | unknown |
| Melting point | 1800 K |
| Boiling point | — |
| Density | — |
| Electronegativity (Pauling) | 1.3 |
| Radioactive | Yes — no stable isotope |
| Origin | synthetic |
| Discovered | 1952 · Ghiorso et al. |
Key facts about Fermium
- Also first found in hydrogen-bomb debris; named after Enrico Fermi.
- The heaviest element that can be made by bombarding lighter elements with neutrons in a reactor.
- Beyond fermium, elements must be built by smashing whole atomic nuclei together.
- Only ever made in quantities of a few million atoms at a time.
What Fermium is used for
None — pure scientific research.
Where it sits in the periodic table
Fermium is in the actinide series, period 7, of the f-block. Its electron configuration [Rn] 5f12 7s2 means its outermost shell holds 2 electrons, which is what places it here and explains much of its chemistry. See Fermium on the interactive table →
Fermium — frequently asked questions
What is Fermium used for?
None — pure scientific research.
Is Fermium radioactive?
Yes. Fermium has no stable isotope, so every form of it is radioactive.
What is the electron configuration of Fermium?
Fermium has the electron configuration [Rn] 5f12 7s2, which is 2, 8, 18, 32, 30, 8, 2 electrons per shell.
What group and period is Fermium in?
Fermium is in the actinide series (f-block), period 7, in the f-block. Its outer shell holds 2 electrons.
Who discovered Fermium?
Fermium was discovered in 1952 by Ghiorso et al..