Berkelium (Bk)
“A city you can find on any map lives inside the periodic table — berkelium honours Berkeley, whose labs built much of the synthetic world.”
How its electrons are arranged
Computed from the aufbau principle, with known real-world exceptions applied automatically.
The notes
Characteristics
- So scarce that world production is counted in micrograms to milligrams per year, and only a couple of facilities on Earth can supply it.
- A rare actinide that moves readily between its +3 and +4 oxidation states, giving chemists a window into tetravalent actinide bonding.
- All twenty-odd known isotopes are radioactive: Bk-247 survives longest (about 1,400 years), while the workhorse Bk-249 lasts just 330 days.
- Made by neutron bombardment of curium in high-flux reactors — one of the heaviest elements that can be stockpiled at all.
A silvery, very heavy radioactive metal that has only ever existed in milligram specks. Nobody has held a visible lump; what chemists know of berkelium comes from microgram samples and spectroscopy rather than from any chunk you could put on a bench.
Where you meet it
✦ Uses
- Target material for superheavy-element hunts: a precious 22-milligram batch of Bk-249 from Oak Ridge was flown to Dubna, where firing calcium-48 beams at it created tennessine, element 117.
- Actinide chemistry research: the accessible +4 state of Bk-249 helped chemists assemble the first berkelium organometallic molecule, a “berkelocene”, in 2018.
- Radiochemical tracer and calibration studies, since Bk-249’s well-mapped decay scheme makes its atoms easy to identify in experiments.
◍ Everyday examples
- When tennessine joined the periodic table in 2016, it arrived thanks to berkelium — a student can trace the newest complete row of the table back to that single 22-milligram shipment.
- Berkelium never appears in shops, homes or hospitals; for a Bangladeshi student it exists purely at the superheavy end of the classroom chart.
History & name
In December 1949 Stanley Thompson, Albert Ghiorso and Glenn Seaborg at the University of California, Berkeley, fired alpha particles at a hard-won americium-241 target in the 60-inch cyclotron; each fusion knocked out two neutrons and left berkelium-243. It was the fifth element humanity had made beyond uranium, and the name matched the team’s own campus town — just as terbium, sitting above berkelium, had been named after the Swedish village of Ytterby. Modern berkelium is not made this way: Oak Ridge’s High Flux Isotope Reactor soaks curium targets in neutrons for months, turning out Bk-249 for researchers around the world.