100[257]FmFermium
Fermium (Fm) — element 100actinide · period 7
Fermium is a chemical element with the symbol Fm and atomic number 100. It is an actinide in period 7 of the periodic table (the f-block), with a standard atomic mass of [257] u. At room temperature (25 °C) fermium is predicted to be a solid.
💡 Known for: Named after Enrico Fermi; the heaviest element that can be made by bombarding lighter elements with neutrons.
# Fermium properties
| Symbol | Fm |
|---|---|
| Atomic number | 100 |
| Atomic mass | [257] u |
| Category | actinide |
| Group | — (f-block, no group number) |
| Period | 7 |
| Block | f-block |
| Electron configuration | [Rn] 5f¹² 7s² |
| Full configuration | 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹² 6s² 6p⁶ 7s² |
| Electrons per shell | 2, 8, 18, 32, 30, 8, 2 |
| Protons / electrons | 100 / 100 |
| State at 25 °C | predicted solid |
| Melting point | 1800 K (1526.8 °C, 2780.3 °F) (predicted) |
| Boiling point | unknown |
| Density | — |
| Electronegativity (Pauling) | 1.3 |
| First ionization energy | 6.5 eV |
| Atomic radius | — |
| Discovered | 1952 |
Values for superheavy elements are theoretical predictions; none have been measured in bulk.
# Electron configuration of fermium
The electron configuration of fermium is [Rn] 5f¹² 7s², written out in full as 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹² 6s² 6p⁶ 7s². Its 100 electrons fill 7 shells as 2, 8, 18, 32, 30, 8, 2, so the outermost shell holds 2 electrons. Because only a few atoms have ever been made, this configuration is a theoretical prediction.
# Related elements
EsEinsteiniumprevious elementMdMendeleviumnext elementAcActiniumactinideThThoriumactinidePaProtactiniumactinideUUraniumactinideNpNeptuniumactinidePuPlutoniumactinideAmAmericiumactinideCmCuriumactinide
# Fermium FAQ
What is the atomic number of fermium?
The atomic number of fermium is 100: every fermium atom has 100 protons in its nucleus. Its symbol is Fm.
What is the atomic mass of fermium?
The standard atomic mass of fermium is [257] u (the mass number of its longest-lived isotope, since it has no stable isotopes).
What is the electron configuration of fermium?
Fermium's electron configuration is [Rn] 5f¹² 7s² (1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹² 6s² 6p⁶ 7s²), with 2, 8, 18, 32, 30, 8, 2 electrons per shell.
Is fermium a metal?
Yes. Fermium is an actinide, one of the metals.
What is the melting point of fermium?
Fermium melts at 1800 K (1526.8 °C, 2780.3 °F). These values are predictions.
What is fermium used for / known for?
Named after Enrico Fermi; the heaviest element that can be made by bombarding lighter elements with neutrons.