Element 100 · Actinide
Fermium (Fm) — Element 100
Enrico Fermi
Fermium (Fm) is an actinide in Period 7 (f-block) of the periodic table with atomic number 100, standard atomic weight [257] u, and ground-state electron configuration [Rn] 5f¹² 7s². At standard temperature and pressure it is classified as a short-lived synthetic nuclide with 3 valence electrons and common oxidation states +3.
Research only
What are the atomic properties and physical constants of Fermium?
Reference constants compiled from IUPAC standard atomic weights, the NIST Atomic Spectra Database, and the CRC Handbook.
- Atomic number (Z)
- 100
- Standard atomic mass
- [257] u
- Chemical family
- Actinide
- Ground-state configuration
- [Rn] 5f¹² 7s²
- Electrons per shell
- 2, 8, 18, 32, 30, 8, 2
- Valence electrons
- 3
- Common ion charges / oxidation states
- +3
- Phase at STP
- Synthetic
- Pauling electronegativity
- 1.30 Pauling
- First ionization energy
- 627 kJ/mol
- Atomic radius
- —
- Melting point
- 1,527 °C
- Boiling point
- —
- Discovery year
- 1952
- Table coordinate
- Period 7, f-block
- Radioactivity
- Radioactive (no stable isotopes)
How are electrons arranged across Fermium’s shells?
A neutral Fermium atom contains 100 electrons distributed across 7 occupied principal energy shells ([Rn] 5f¹² 7s²). The table below compares Fermium’s shell occupancy against each shell’s theoretical 2n² capacity.
| Principal Shell (n) | Spectroscopic Letter | Electrons in Fm | Max Shell Capacity (2n²) |
|---|---|---|---|
| n = 1 | K | 2 e⁻ | 2 e⁻ |
| n = 2 | L | 8 e⁻ | 8 e⁻ |
| n = 3 | M | 18 e⁻ | 18 e⁻ |
| n = 4 | N | 32 e⁻ | 32 e⁻ |
| n = 5 | O | 30 e⁻ | 50 e⁻ |
| n = 6 | P | 8 e⁻ | 72 e⁻ |
| n = 7 | Q | 2 e⁻ | 98 e⁻ |
Frequently Asked Questions about Fermium (Fm)
What is the atomic mass and atomic number of Fermium (Fm)?
Fermium (Fm) has atomic number Z = 100 (100 protons in its nucleus) and an IUPAC standard atomic weight of [257] u. It sits in Period 7 in the f-block and is classified as an actinide.
What is the ground-state electron configuration of Fermium?
The neutral ground-state electron configuration of Fermium (Z = 100) is [Rn] 5f¹² 7s². Across its 7 occupied principal shells (n = 1 to n = 7), the electrons per shell are 2, 8, 18, 32, 30, 8, 2, with 3 valence electrons participating in bonding.
What are the common ion charges and electronegativity of Fermium?
Fermium commonly forms +3 oxidation states or ion charges in compounds. Its Pauling electronegativity is 1.30 and its first ionization energy is 627 kJ/mol.
When was Fermium discovered and what is it used for?
Fermium was discovered in 1952 (Enrico Fermi). Research only
How does Fermium compare to neighboring elements?
Other actinide elements: