Berkelium
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.
Identity
- Atomic mass
- 247 u
- Category
- Actinides
- Group
- 3
- Period
- 7
- Block
- f
- Oxidation States
- +3, +4
- Phase (25 °C)
- Solid
- Appearance
- silvery
Electronic Structure
- Electron configuration
- 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p6 6s2 4f14 5d10 6p6 7s2 5f9
- Short configuration
- [Rn] 5f9 7s2
- Electrons per shell
- 2, 8, 18, 32, 27, 8, 2
- Electronegativity (Pauling)
- 1.30
- Electron affinity
- -165 kJ/mol
- 1st ionization energy
- 601 kJ/mol
Physical properties
- Melting point
- 985.9 °C (1259 K)
- Boiling point
- 2626.8 °C (2900 K)
- Density
- 14.78 g/cm³
- Molar heat capacity
- —
Chemical behavior of berkelium
Berkelium has nine outer electrons ([Rn] 5f⁹ 7s²) and acts as +3, with a stable +4 in the dioxide and fluorides. Its electronegativity is low (1.30) and it is dense, malleable, and highly radioactive: it is produced in micrograms and heats its compounds. It is terbium's twin among the actinides; Bk-249, a beta emitter, is the target that engendered tennessine.
Reactivity
4 Bk + 3 O₂ → 2 Bk₂O₃
In air it rapidly oxidizes to the dark dioxide. The heat of decay keeps the sample warm and speeds up the oxidation.
2 Bk + 6 HCl → 2 BkCl₃ + 3 H₂
It dissolves in acids to give greenish berkelium(III) salts. The chloride is the route for purifying Bk-249 from neighboring curium.
BkO₂ + 4 HF → BkF₄ + 2 H₂O
The dioxide converts to the tetrafluoride, the precursor of the metal by reduction with lithium and of ultrapure targets.
²⁴⁹Bk → ²⁴⁹Cf + β
Bk-249 decays into californium-249 by beta emission: every tennessine target carries this 330-day countdown.
Notable compounds
| Compound | Formula | Use or importance |
|---|---|---|
| Berkelium-249 dioxide | ²⁴⁹BkO₂ | Target for tennessine 117 |
| Berkelium tetrafluoride | BkF₄ | Metal production |
| Berkelium chloride | BkCl₃ | Curium purification |
| Berkelium oxalate | Bk₂(C₂O₄)₃ | Radiochemical separation |
| Bk-Cm mixed oxide | BkCmO₂ | Accelerator targets |
Electron shell distribution
View in the atom builderIsotopes
No berkelium isotope is stable and less than a gram is produced per year. Berkelium-249 (²⁴⁹Bk, 330 days) is the tennessine target and decays into Cf-249. Berkelium-247 (²⁴⁷Bk, 1,380 years) is the longest-lived but even scarcer.
Occurrence and production
It does not exist in nature: all berkelium is bred in high-flux reactors, when Cm-244 captures neutrons up to Bk-249. It is separated from curium and californium by chromatography at Oak Ridge: each campaign of months yields milligrams.
History and origin of the name
Thompson, Ghiorso, and Seaborg synthesized it in 1949 by bombarding americium with alphas in Berkeley and named it berkelium, after Berkeley: local pride after continental americium. The Bk-249 campaign for tennessine (2009) cost years and millions.
Applications and relevance of berkelium
Uses of the element
As Bk-249 in microgram targets, bombarded with calcium-48, it engendered the tennessine atoms that completed row 117. Without berkelium there would be no tennessine.
Uses of its compounds
The electrodeposited dioxide forms the accelerator target; the fluorides purify the metal for targets. Its solutions calibrate superheavy chemistry.
Health, safety and environment
Biological role
It has no biological function and is highly radiotoxic: it accumulates in bone and liver. Work is done in nanograms with double containment and beta-gamma contamination control.
Safety
It is handled only at Oak Ridge and Dubna, in cells with robots and shielding. Bk-249 produces daughter Cf-249, which demands increasing neutron shielding. It does not exist in products.
Environment
There are no spills: all inventory is traceable and waste is vitrified. Its production consumes entire reactors for months to yield milligrams.
Frequently asked questions about Berkelium
What is berkelium-249 used for in superheavy element synthesis?
Berkelium-249 is used as starting material to synthesize superheavy elements such as tennessine, element 117. By bombarding berkelium-249 atoms with calcium-48 ions in an accelerator, nuclei of heavier elements that do not exist naturally can be formed. These syntheses require tiny amounts of berkelium, but enough for the accelerated ions to collide with its nuclei.
What role did berkelium play in the discovery of tennessine?
Berkelium-249 was the target material used to synthesize tennessine, element 117, by bombarding it with calcium-48 ions. This synthesis, carried out at Oak Ridge National Laboratory, required tiny amounts of berkelium but enough for the accelerated ions to collide with its nuclei and form tennessine atoms. The discovery confirmed the existence of a new element of the periodic table.
Why is berkelium named that way?
Berkelium was named after the city of Berkeley, California, where it was discovered in 1949 by Stanley Thompson, Albert Ghiorso, and Glenn Seaborg. It was produced by bombarding americium-241 with alpha particles in a cyclotron. The name recognizes the role of the University of California, Berkeley as a pioneering center in the synthesis of transuranium elements.
What is berkelium's relationship to the periodic table?
Berkelium is element 97 and part of the actinides, the series of radioactive metallic elements that runs from actinium to lawrencium. Its position in the periodic table places it between curium and californium. As an actinide it shares chemical properties with the other elements of the series, but all of its isotopes are radioactive and its production is extremely limited.
Why is berkelium so difficult to produce?
Berkelium is produced in amounts of less than one gram per year worldwide, because of the difficulty of its synthesis and the complexity of its separation. It can only be obtained in nuclear reactors or particle accelerators, and its yield is very low. This extreme scarcity explains why it has no commercial applications and why its study is limited to fundamental research.
What is the difference between berkelium and californium in research?
Californium, especially isotope 252, has practical applications as a neutron source, whereas berkelium is used almost exclusively in fundamental research and as starting material to synthesize superheavy elements. Californium is produced in larger quantities and has industrial uses, while berkelium is scarcer and more experimental. Both are synthetic radioactive actinides, but with very different roles.
Which berkelium isotopes are the most relevant?
Berkelium-249 is the most studied isotope and the one used as starting material to synthesize superheavy elements. It has a half-life of about 330 days and emits beta radiation. Other isotopes, such as berkelium-247, have longer half-lives but are harder to produce. The choice of isotope depends on the application and the required duration.
Main sources consulted: PubChem, Royal Society of Chemistry, NIST, IUPAC. Last revision: November 2026.