Berkelium (Bk)
Berkelium (symbol Bk) is the chemical element with atomic number 97: an actinide, solid at 0 °C, radioactive, made artificially, with an atomic mass of 247 u. Discovered in 1949 (Glenn T. Seaborg et al.).
Berkelium, named after the city of Berkeley, California, is a synthetic metal produced in minuscule amounts: a few milligrams at a time, in essentially a single reactor in the world. It has no practical use, but it served as an essential target for making element 117, tennessine. Its most stable isotope, berkelium-247, has a half-life of about 1,400 years.
Key facts
- Atomic number
- 97
- Symbol
- Bk
- French name
- Berkélium
- Atomic mass
- 247 u
- Molar mass
- [247] g/mol
- Family
- Actinides
- Position
- period 7, f-block
- State at 0 °C
- Solid
- Melting point
- 985.9 °C
- Boiling point
- 2,626.9 °C
- Density
- 14.78 g/cm³
- Electronegativity (Pauling)
- 1.3
- First ionization energy
- 601 kJ/mol
- Atomic radius
- 170 pm
- Electron configuration
- [Rn] 5f⁹ 7s²
- Indicative price
- 190 billion $/kg (order of magnitude)
- Radioactive
- yes
- Discovery
- 1949, Glenn T. Seaborg et al.
Origin of the name
From Berkeley, the university town in California.
What does berkelium look like?
A soft, silvery metal, first obtained in pure form in 1969. It is highly radioactive, and its compounds are often colorful (green, yellow, brown).
Where is berkelium found?
Absent from nature. It exists only in a handful of specialized laboratories.
How is berkelium produced?
It is made at the High Flux Isotope Reactor (HFIR) at Oak Ridge, Tennessee, by bombarding curium with neutrons for months. The atoms capture neutron after neutron until they become berkelium-249, which is then separated chemically.
Top producers
- United States (Oak Ridge)
- Russia (Dimitrovgrad)
What is berkelium used for?
- Basic research only
- Target for synthesizing tennessine (element 117)
- Production of californium-249, itself used as a target
In everyday life
- None — it exists only in milligrams in a few laboratories
Role in living things
No biological role. It would accumulate in the bones.
Hazards of berkelium
Radioactive and radiotoxic; it is handled only in glove boxes by specialists.
Cosmic origin
- Human-made: Does not exist (or barely) in nature: synthesized in a reactor or accelerator.
History of berkelium
In December 1949, Stanley Thompson, Albert Ghiorso and Glenn Seaborg bombarded americium-241 with alpha particles in the Berkeley cyclotron and obtained berkelium-243. The name follows the logic of terbium, which sits above it and was named after the Swedish village of Ytterby.
Did you know?
- In 2009, Oak Ridge produced 22 milligrams of berkelium-249 after about 250 days of irradiation, then shipped it to Dubna, Russia, to make element 117.
- The package had to cross the Atlantic several times after Russian customs turned it back over incomplete paperwork — while berkelium-249 loses half its atoms in just under a year.
- The first berkelium compound ever weighed, a chloride prepared in 1962, came to just a few billionths of a gram.
Isotopes of berkelium
No stable isotopes; berkelium is produced only in milligram quantities, in a handful of specialized reactors.
- berkelium-243: radioactive, half-life 4.6 h. The element's first synthesized isotope, in 1949.
- berkelium-247: radioactive, half-life 1,380 years. The longest-lived.
- berkelium-249: radioactive, half-life 330 days. The target that made it possible to create tennessine in 2010.
Related elements
Same family (actinides): Actinium (Ac), Thorium (Th), Protactinium (Pa), Uranium (U), Neptunium (Np), Plutonium (Pu), Americium (Am), Curium (Cm), Californium (Cf), Einsteinium (Es), Fermium (Fm), Mendelevium (Md), Nobelium (No), Lawrencium (Lr).