- Berkelium (Bk) is a silvery, radioactive metal with atomic number 97, belonging to the actinide series.
- Its electron configuration is [Rn] 5f⁹ 7s², and it commonly exhibits oxidation states of +3 and +4, with +3 being the most stable in aqueous chemistry. The atomic structure contains ninety-seven protons, most often one hundred and fifty-two neutrons in berkelium-249 (²⁴⁹Bk), and ninety-seven electrons arranged in seven shells.
- Berkelium does not occur naturally; it is synthesized in nuclear reactors by prolonged neutron irradiation of lighter actinides such as americium or curium. The most notable isotopes are berkelium-247 (²⁴⁷Bk), with a half-life of 1,380 years, and berkelium-249 (²⁴⁹Bk), with a half-life of 330 days, which is most often used in research because it can be produced in gram quantities.
- Berkelium was first synthesized in December 1949 by Stanley G. Thompson, Glenn T. Seaborg, and Albert Ghiorso at the University of California, Berkeley, by bombarding americium-241 (²⁴¹Am) with alpha particles in a cyclotron, producing berkelium-243 (²⁴³Bk), which decayed via beta emission to californium-243. The element was named after the city of Berkeley, California, where it was discovered—making it one of the few elements named for a specific location.
- Berkelium’s main significance is as an intermediate in the synthesis of heavier transuranium and transactinide elements, such as lawrencium and tennessine. Notably, berkelium-249 was used as the target material for the synthesis of element 117, tennessine (Ts), in 2010. It has no large-scale commercial applications due to its scarcity, short half-lives, and high radioactivity.
- Chemically, berkelium resembles other trivalent actinides and rare earth metals. Metallic berkelium is soft and reactive, tarnishing in air to form a thin oxide layer. Berkelium(III) oxide (Bk₂O₃) is its most stable compound, while the +4 oxidation state occurs in strong oxidizing environments, forming compounds like berkelium(IV) oxide (BkO₂). Berkelium also forms halides such as BkF₃, BkCl₃, and BkBr₃, and it participates in coordination chemistry with ligands such as nitrates and phosphates.
- Biologically, berkelium has no natural role in living organisms and is extremely radiotoxic. Inhaled or ingested berkelium tends to accumulate in bones and the liver, where its alpha radiation can cause severe cellular damage. Due to its short-lived isotopes and intense radiation, handling berkelium requires specialized facilities with remote manipulation and heavy shielding.
- Environmentally, berkelium exists only where it has been intentionally produced, primarily in high-flux nuclear reactors. It contributes to the radiotoxicity of nuclear waste, though in much smaller quantities than isotopes of plutonium or americium.
