ElementsWhat is californium?
Californium is a radioactive metal made in special reactors. It is a strong source of neutrons.
What is californium used for?
Starting up nuclear reactors, finding oil and water layers in wells, and detecting gold and silver in ores.
Where the name comes from
From California, the state where it was first made.
Key facts
- Symbol
- Cf
- Atomic number
- 98
- Atomic mass
- 251.07959 u
- Family
- Actinide
- Period
- 7
- Group
- none (f-block)
- Block
- f
- State at room temperature
- Solid
- Melting point
- 899.9 °C (1,173 K, 1,652 °F)
- Boiling point
- not measured
- Density
- not measured
- Electrons per shell
- 2, 8, 18, 32, 28, 8, 2
- Electron configuration
- [Rn]7s2 5f10
- Common oxidation states
- +3
- Electronegativity (Pauling)
- 1.3
- First ionisation energy
- 6.3 eV
- Electron affinity
- no value
- Atomic radius (van der Waals)
- 245 pm
- Discovered
- 1950
Place in the periodic table
Californium is element number 98. It sits in period 7 (row 7) of the periodic table, in the separate row of actinides drawn below the main table, and belongs to the f-block. Just before it comes berkelium (97), and just after it comes einsteinium (99).
Family: Actinides.
Physical properties
At room temperature californium is a solid. Its melting point is about 899.9 °C. Its boiling point has not been measured reliably.
Inside the atom
An atom of californium has 98 protons in its nucleus and, when neutral, 98 electrons around it. The electrons are arranged in 7 shells: 2, 8, 18, 32, 28, 8, 2. The outermost shell holds 2 electrons. Written in full, the electron configuration is [Rn]7s2 5f10.
Its electronegativity on the Pauling scale is 1.3. This number shows how strongly an atom pulls shared electrons towards itself: fluorine, the strongest, is 3.98. Removing one electron from an atom takes 6.3 electronvolts (about 608 kilojoules per mole). One mole of californium weighs 251.07959 grams, so a single gram contains about 2.40 × 1021 atoms.
The ring picture is a simple model that only counts the electrons in each shell. Real atoms do not look like this.
Next steps
- Work out the weight of a compound that contains californium with the molar mass calculator.
- Compare it with every other element in the sortable list.
- Test yourself with the symbol quiz.
Figures on this page are from PubChem (U.S. National Library of Medicine), as downloaded on 11 November 2026. See About and data sources.