ELEMENTLE

Element 97 · Actinide

Berkelium

Period 7

Berkelium is a transuranic radioactive chemical element with symbol Bk and atomic number 97. It is a member of the actinide and transuranium element series. It is named after the city of Berkeley, California, the location of the University of California Radiation Laboratory where it was discovered in December 1949.

Three reasons Berkelium stands out

  1. 1

    Named after Californian city, home to one of the world's top STEM universities.

  2. 2

    Only a few billion atoms of it have ever been produced in total, making it extraordinarily rare even by synthetic element standards.

  3. 3

    It was first synthesised in 1949 by bombarding another synthetic element with alpha particles.

A laboratory element named for a laboratory city

Berkelium was first produced at the University of California, Berkeley, continuing a geographic naming chain that includes terbium and californium. It exists only in tiny manufactured quantities. Even so, a carefully prepared berkelium target enabled the creation of tennessine decades later.

Berkelium at a glance
Atomic number / protons97
SymbolBk
Family (Elementle)Actinide
Classification (PubChem)Actinide
Period7
GroupLanthanide / actinide series
Atomic mass (u)247.07031
Standard stateSolid
Electron configuration[Rn]7s2 5f9
Reported oxidation states+4, +3
Electronegativity (Pauling)1.3
Atomic radius (pm)244
First ionization energy (eV)6.23
Electron affinity (eV)Not available
Density (g/cm³)14
Melting point1323 K (1,049.85 °C)
Boiling pointNot available
Discovery (PubChem)1949

Values are reference data, not a specification for every temperature, pressure, or allotrope. Unknown properties are left unavailable. Superheavy-element predictions remain uncertain.

Sources & further reading

PubChem: Berkelium · Berkelium on Wikipedia

The introduction and original editorial story are adapted from Wikipedia contributors via Periodic-Table-JSON. Element descriptions and their adaptations are available under CC BY-SA 3.0. Numerical attributes use the PubChem periodic-table dataset, retrieved September 22, 2026.