Californium (Cf): Electron Configuration, Properties and Uses
Californium (Cf): Electron Configuration, Properties and Uses
Electron configuration [Rn] 7s2 5f10 · f-block, actinide series · period 7 · Ar [251]
Californium data
- Atomic number
- 98
- Relative atomic mass
- [251]
- Group
- – (actinide series)
- Period
- 7
- Block
- f
- Category
- Actinide
- Electron configuration
- [Rn] 7s2 5f10
- Full configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f10
- Electrons per shell
- 2, 8, 18, 32, 28, 8, 2 (K L M N O P Q)
- Valence electrons
- 2 (in the outer shell)
- Electronegativity (Pauling)
- 1.3
- First ionisation energy
- 6.3 eV
- Atomic radius (van der Waals)
- 245 pm
- State at room temperature
- Solid
- Melting point
- 900 °C
- Boiling point
- no data
- Density
- no data
- Common oxidation states
- +3
- Discovered
- 1950
Source: PubChem (NIH, accessed 13 Nov 2026); atomic mass: IUPAC standard atomic weight.
Electron shell diagram
K 2 · L 8 · M 18 · N 32 · O 28 · P 8 · Q 2
Orbital diagram (outer electrons)
About californium
Californium, symbol Cf, is element number 98 in the periodic table. It belongs to the actinide series in period 7 (f-block), usually shown below the main table. Californium was first discovered in 1950. It is named after the state of California. Californium is a solid at room temperature, melting at 900 °C.
Californium electron configuration
The electron configuration of californium is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f10, or in short [Rn] 7s2 5f10. Its electrons occupy 7 shells: K = 2, L = 8, M = 18, N = 32, O = 28, P = 8, Q = 2. As an actinide, californium fills the 5f subshell. Its outer 7s subshell holds 2 electrons; valence electrons for this series are not assigned by the usual group rule. When it forms cations, electrons leave the outermost subshell first: Cf3+ = [Rn] 5f9.
Filling order: 1s2(2) → 2s2(4) → 2p6(10) → 3s2(12) → 3p6(18) → 4s2(20) → 3d10(30) → 4p6(36) → 5s2(38) → 4d10(48) → 5p6(54) → 6s2(56) → 4f14(70) → 5d10(80) → 6p6(86) → 7s2(88) → 5f10(98)
Uses of californium
Well-known applications of californium include Cf-252 as a neutron source for starting reactors, materials analysis and explosives detection.
Safety
Californium is radioactive. Using, storing or transporting radioactive material requires a licence from the national regulator (BAPETEN in Indonesia). Always read the safety data sheet (SDS) before working with a chemical.
Other actinides
Frequently asked questions
What is the electron configuration of californium?
The electron configuration of californium (Cf, atomic number 98) is 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f10, or [Rn] 7s2 5f10 in short. By shell: 2, 8, 18, 32, 28, 8, 2.
How many valence electrons does californium have?
Californium has 2 electrons in its outer shell. For lanthanides and actinides, valence electrons are not assigned by the usual group rule.
Which group and period is californium in?
Californium is in the actinide series, period 7, f-block.
What is the atomic mass of californium?
Californium has no stable isotope, so the mass number of its longest-lived isotope, [251], is given.
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