#98 / 118
98Cf[251]
Actinidessolid at STPF-block

Californium

Group: f-blockPeriod: 7Standard Atomic Weight: [251] u

Why is Californium in this position?

Understanding the scientific rationale behind Californium's position in the periodic table:

Group Assignment
Group Lanthanide / Actinide

Actinide series element filling the 5f subshell.

Period Assignment
Period 7

Belongs to Period 7 because its outermost electrons occupy n=7.

Orbital Block
F-block

Belongs to the f-block because valence electrons fill 5f orbitals (5f¹⁰ 7s²).

Chemical Category
Actinides

Classified as an actinide radioactive synthetic metal.

Atomic Structure & Bohr Shell Model

Shell Distribution: [2, 8, 18, 32, 28, 8, 2]

Bohr Atomic Shell Model(2, 8, 18, 32, 28, 8, 2)

Hover or tap any shell orbit ring to inspect electron counts and 2n² capacities.

98 Protons (p⁺)153 Neutrons (n⁰)
KShell K: Electron 1 of 2Shell K: Electron 2 of 2LShell L: Electron 1 of 8Shell L: Electron 2 of 8Shell L: Electron 3 of 8Shell L: Electron 4 of 8Shell L: Electron 5 of 8Shell L: Electron 6 of 8Shell L: Electron 7 of 8Shell L: Electron 8 of 8MShell M: Electron 1 of 18Shell M: Electron 2 of 18Shell M: Electron 3 of 18Shell M: Electron 4 of 18Shell M: Electron 5 of 18Shell M: Electron 6 of 18Shell M: Electron 7 of 18Shell M: Electron 8 of 18Shell M: Electron 9 of 18Shell M: Electron 10 of 18Shell M: Electron 11 of 18Shell M: Electron 12 of 18Shell M: Electron 13 of 18Shell M: Electron 14 of 18Shell M: Electron 15 of 18Shell M: Electron 16 of 18Shell M: Electron 17 of 18Shell M: Electron 18 of 18NShell N: Electron 1 of 32Shell N: Electron 2 of 32Shell N: Electron 3 of 32Shell N: Electron 4 of 32Shell N: Electron 5 of 32Shell N: Electron 6 of 32Shell N: Electron 7 of 32Shell N: Electron 8 of 32Shell N: Electron 9 of 32Shell N: Electron 10 of 32Shell N: Electron 11 of 32Shell N: Electron 12 of 32Shell N: Electron 13 of 32Shell N: Electron 14 of 32Shell N: Electron 15 of 32Shell N: Electron 16 of 32Shell N: Electron 17 of 32Shell N: Electron 18 of 32Shell N: Electron 19 of 32Shell N: Electron 20 of 32Shell N: Electron 21 of 32Shell N: Electron 22 of 32Shell N: Electron 23 of 32Shell N: Electron 24 of 32Shell N: Electron 25 of 32Shell N: Electron 26 of 32Shell N: Electron 27 of 32Shell N: Electron 28 of 32Shell N: Electron 29 of 32Shell N: Electron 30 of 32Shell N: Electron 31 of 32Shell N: Electron 32 of 32OShell O: Electron 1 of 28Shell O: Electron 2 of 28Shell O: Electron 3 of 28Shell O: Electron 4 of 28Shell O: Electron 5 of 28Shell O: Electron 6 of 28Shell O: Electron 7 of 28Shell O: Electron 8 of 28Shell O: Electron 9 of 28Shell O: Electron 10 of 28Shell O: Electron 11 of 28Shell O: Electron 12 of 28Shell O: Electron 13 of 28Shell O: Electron 14 of 28Shell O: Electron 15 of 28Shell O: Electron 16 of 28Shell O: Electron 17 of 28Shell O: Electron 18 of 28Shell O: Electron 19 of 28Shell O: Electron 20 of 28Shell O: Electron 21 of 28Shell O: Electron 22 of 28Shell O: Electron 23 of 28Shell O: Electron 24 of 28Shell O: Electron 25 of 28Shell O: Electron 26 of 28Shell O: Electron 27 of 28Shell O: Electron 28 of 28PShell P: Electron 1 of 8Shell P: Electron 2 of 8Shell P: Electron 3 of 8Shell P: Electron 4 of 8Shell P: Electron 5 of 8Shell P: Electron 6 of 8Shell P: Electron 7 of 8Shell P: Electron 8 of 8QShell Q: Electron 1 of 2Shell Q: Electron 2 of 2CfZ = 98

Educational Note: This Niels Bohr planetary model visually illustrates principal quantum energy shells ($n=1, 2, 3\dots$) and electron counts. In modern quantum mechanics (Schrödinger model), electrons do not orbit in fixed circular planetary tracks, but exist as 3D probability clouds (orbitals: $s, p, d, f$) governed by the Heisenberg uncertainty principle.

Electron Shell Filling Breakdown

Shell K (n=1):2 / 2 electrons (100%)
Shell L (n=2):8 / 8 electrons (100%)
Shell M (n=3):18 / 18 electrons (100%)
Shell N (n=4):32 / 32 electrons (100%)
Shell O (n=5):28 / 50 electrons (56%)
Shell P (n=6):8 / 72 electrons (11%)
Shell Q (n=7):2 / 98 electrons (2%)
Aufbau Electron Configuration
1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ 4s² 4p⁶ 4d¹⁰ 4f¹⁴ 5s² 5p⁶ 5d¹⁰ 5f¹⁰ 6s² 6p⁶ 7s²

Neutral ground state configuration. Valence electrons: 12.

Atomic & Quantum Properties

Electronegativity (Pauling)1.3 Pauling
1st Ionization Energy608 kJ/mol
Electron Affinity-45 kJ/mol
Atomic Radius (empirical)168 pm
Common Oxidation States+3
Crystal StructureDouble HCP

Physical & Thermal Properties

Density at STP15.1 g/cm³
Melting Point900 °C (1173 K)
Boiling Point1470 °C (1743 K)
Magnetic OrderingParamagnetic
Discovery Year1950
Discovered ByStanley G. Thompson, Kenneth Street Jr., Albert Ghiorso & Glenn T. Seaborg

Real-World Uses, Occurrence & Compounds

Major Industrial & Everyday Uses
  • Portable neutron startup sources initiating chain reactions in commercial nuclear reactors
  • Neutron activation analysis for mineral exploration and airport luggage explosives detection
  • Neutron moisture gauges identifying subterranean water and petroleum reservoirs
  • Target for synthesis of superheavy element Oganesson (element 118)
Occurrence in Nature

Synthesized in high-flux nuclear reactors at Oak Ridge and Dimitrovgrad; costs roughly $27 million per gram.

Etymology & Name Origin

Named after the State of California and the University of California, Berkeley

Important Chemical Compounds
Cf₂O₃ (Californium(III) oxide)
CfCl₃ (Californium trichloride)
Interesting Chemical Facts
  • Californium-252 is such a ferocious neutron emitter that one microgram emits 139 million neutrons every minute via spontaneous nuclear fission.
  • Californium is the heaviest chemical element ever isolated in macroscopic, weighable quantities visible to the naked human eye.
  • Bombarding a Californium-249 target with Calcium-48 ions at Dubna, Russia produced the very first atoms of element 118 (Oganesson).
Safety & Handling Note

Extremely radiotoxic; intense spontaneous neutron radiation requires heavy paraffin or water shielding.