Fermium

01 / A closer look

Meet Fermium

Fermium has atomic number 100: every atom of this element contains 100 protons. It belongs to period 7 of the periodic table.

In a neutral atom, the number of electrons equals the number of protons. Isotopes of this element share the same atomic number but have different neutron counts.

02 / Physical properties

Melting point

1800 K

Reference estimate; not an established bulk measurement

Boiling point

Not listed

Density

Not listed

Isotope mass number

[257]

Melting points, boiling points and densities follow RSC fact boxes. Density is referenced to room temperature; consult the source for pressure and allotrope details. These are reference values, not a claim that every value was experimentally measured. Atomic weights follow CIAAW.

Physical-property source: Royal Society of Chemistry ↗ · Reviewed 24 September 2026

Standard atomic weights follow CIAAW 2024 (abridged). Brackets show an isotope mass number from IUPAC 2022, not a standard atomic weight.

03 / Atomic structure

Atomic structure

Electron configuration

[Rn] 5f12 7s2

Oxidation states

+3

Electronegativity · Pauling

1.3

First ionisation energy

6.50 eV

Atomic radius

Not listed

04 / Where it is found

Where it is found

Produced artificially in minute quantities.

Production and export figures depend on the commodity and reporting year. No comparable country quantities have been included for this element in this edition.