Periodic TableFermium (Fm)
Fermium is an actinide with atomic number 100, in period 7, in the f-block of the periodic table. Its atomic mass is 257 u and its electron configuration is [Rn] 5f¹² 7s².
Key facts
| Atomic number | 100 |
|---|---|
| Atomic mass | 257 u |
| Category | Actinide |
| Period | 7 |
| Group | f-block, no group number |
| Block | f |
| Electron configuration | [Rn] 5f¹² 7s² |
| Electrons per shell | 2, 8, 18, 32, 30, 8, 2 |
| Electronegativity (Pauling) | 1.3 |
| Oxidation states | +2, +3common in bold |
| State at 25 °C | --- |
| Melting point | 1800 K1526.85 °C |
| Boiling point | --- |
| Density | 9.7 g/cm³ |
Atomic properties
| First ionization energy | 6.5 eV |
|---|---|
| Electron affinity | --- |
| Atomic radius | --- |
| Covalent radius | --- |
| Van der Waals radius | --- |
| Common ions | Fm³⁺ |
| Protons, neutrons, electrons | 100, 157, 100 |
Physical and thermal properties
| Molar volume | --- |
|---|---|
| Heat of fusion | --- |
| Heat of vaporization | --- |
| Specific heat | --- |
| Thermal conductivity | --- |
| Thermal expansion | --- |
| Mohs hardness | --- |
| Young’s modulus | --- |
| Crystal structure | Face-centered cubic |
| Magnetic type | --- |
Identification and history
| CAS number | 7440-72-4 |
|---|---|
| Latin name | Fermium |
| Discovered by | L. Berkeley National Laboratory · 1952 |
| Named by | --- |
Natural isotopes
Fermium has no stable isotopes: every isotope is radioactive.
No visible amount of Fermium has ever been made: its physical properties here are theoretical estimates, not measurements.
Data checked against PubChem (NIH), IUPAC, the NIST Atomic Spectra Database and the IAEA (NUBASE and AME), the same data you see in the app.
A dash (---) means there is no reliable published measurement. The app never makes one up.
See Fermium in the app
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