Bk · Element 97 · Actinide
Made in milligram quantities and used mainly as a target for creating even heavier elements.
Structure
Not a diagram of dots on rings — a Monte-Carlo sample of the actual probability density |ψ|² for each occupied subshell. Drag to rotate. Blue and violet mark opposite signs of the wavefunction, which is what makes bonding possible.
Measured values
Every bar shows where berkelium sits among all 118 elements for that property.
Sources: IUPAC 2021 standard atomic weights · CRC Handbook of Chemistry and Physics · NIST. Values marked ~ are predicted rather than measured.
Same element, different neutrons
All berkelium atoms have the same number of protons, 97, and differ only in their number of neutrons: those variants are its isotopes. None of them is stable. The longest-lived known isotope, Bk-247, has 150 neutrons and a half-life of 1380 yrs.
| ISOTOPE | Neutrons | Natural Abundance | Half-life | Decay Mode |
|---|---|---|---|---|
| Bk-245 | 148 | — | 4.95 days | ε |
| Bk-246 | 149 | — | 1.80 days | ε/β⁺ |
| Bk-247 longest-lived | 150 | — | 1380 yrs | α |
| Bk-248 | 151 | — | >9 yrs | — |
| Bk-249 | 152 | — | 330 days | β⁻ |
Here the classroom shortcut, rounded atomic mass (247) minus atomic number, gives the same answer: 150.
Decay modes
Data: IAEA Nuclear Data Section, LiveChart of Nuclides, ground-state evaluations, retrieved October 10, 2026. Abundance is the share of atoms in the natural element; a dash means the isotope has no standard natural abundance.
Size, to scale
Radius 244 pm — that is 0.244 nm, so about 2.05 million of them side by side would span a millimetre.
Thermal range
Berkelium is liquid over a 1577 K window, from 1323 K to 2900 K.
The story
Made in milligram quantities and used mainly as a target for creating even heavier elements.
Berkelium was discovered on December 19, 1949, at the University of California, Berkeley, by a brilliant team of nuclear chemists who were systematically creating new elements beyond uranium.
The berkelium discovery team included some of the most prominent nuclear scientists of the 20th century:
The discovery used Berkeley's 60-inch cyclotron, one of the most powerful particle accelerators of its time:
Confirming berkelium's discovery required great skill:
The berkelium discovery was scientifically important because it:
The discovery team's work was recognized with numerous honors:
Applications
Berkelium represents one of the most challenging frontiers in nuclear research, with applications that push the boundaries of atomic science and our understanding of matter itself.
Berkelium serves as a crucial stepping stone in the synthesis of even heavier elements. The Bk-249 isotope is used as a target material in particle accelerators to create elements 117 (Tennessine) and beyond. These experiments help scientists understand the theoretical "island of stability" - a predicted region where superheavy elements might exist for longer periods.
Despite its rarity, berkelium provides unique insights into actinide chemistry. Researchers study its oxidation states (primarily +3 and +4) to understand electron behavior in the 5f orbital series. These studies are crucial for developing new theories about heavy element chemistry and predicting properties of undiscovered elements.
Berkelium isotopes serve as educational tools in advanced nuclear chemistry courses, helping students understand:
Research with berkelium contributes to the development of advanced nuclear technologies, including improved methods for:
While limited to research, berkelium studies may eventually contribute to:
Berkelium has no commercial applications due to its rarity, short half-life, and high radioactivity. All uses are confined to specialized nuclear research facilities.
Berkelium isotopes serve as reference materials for:
Production Scale: Just over one gram of berkelium has been produced in the United States since 1967, in milligram batches, making it one of the rarest substances on Earth. A typical Oak Ridge processing campaign yields milligrams of berkelium-249 (22 mg for the tennessine experiment).
Where it comes from
0 mg/kg of Earth's crust · more abundant than 0% of elements
Berkelium does not occur naturally on Earth and must be artificially created in nuclear reactors or particle accelerators. It represents humanity's ability to create new forms of matter that do not exist in nature.
Nuclear Reactor Production: The primary method involves bombarding americium-241 with neutrons in high-flux nuclear reactors:
Particle Accelerator Synthesis: Alternative method using heavy ion bombardment:
Berkelium separation is extremely challenging due to:
Only a few facilities worldwide can produce berkelium:
Total Production: Just over 1 gram of berkelium has been produced in the United States since 1967
Current Availability: Typically less than 1 milligram exists worldwide at any given time
Handling
Berkelium is radioactive. It has no stable isotope — every nucleus decays. Handling requires appropriate shielding and licensing.
WARNING: Berkelium-249 is intensely radioactive, about 1,600 curies per gram, and is dangerous mainly if it gets into the body. It poses serious health risks through multiple pathways and requires the highest level of safety protocols.
In case of berkelium exposure or contamination:
Legal Restrictions: Berkelium is regulated by national radiation authorities as radioactive material; it is not nuclear material under the IAEA Statute. Only licensed facilities with specialized equipment and trained personnel may handle it.
Quick answers
Berkelium (symbol Bk) is element 97 on the periodic table, an actinide in period 7. Made in milligram quantities and used mainly as a target for creating even heavier elements. At room temperature it is a solid, and it is radioactive.
[Rn] 5f⁹ 7s², giving 7 occupied shells with the distribution 2, 8, 18, 32, 27, 8, 2.Berkelium melts at 1323 K (1049.9 °C) and boils at 2900 K (2626.9 °C).
Berkelium has no stable isotope, so it has no standard atomic weight. The figure quoted, 247, is the mass number of its longest-lived known isotope.
Berkelium has no stable isotope. Its longest-lived known isotope, Bk-247, has 150 neutrons (mass number 247 minus atomic number 97) and a half-life of 1380 yrs. The classroom shortcut, rounded atomic mass (247) minus atomic number, gives the same 150.
Berkelium has a density of 14.78 g/cm³. Water is 1.0 g/cm³, so a block of berkelium is about 14.8× heavier.
Berkelium has a Pauling electronegativity of 1.3. The scale runs from 0.70 (francium, the least greedy for electrons) to 3.98 (fluorine, the most). Values in this middle band tend to form covalent rather than strongly ionic bonds.
Berkelium was discovered in 1949 by Thompson, Ghiorso & Seaborg. Origin of the name: Berkeley, California.
Berkelium does not occur naturally on Earth in any meaningful quantity — it is made in a reactor or an accelerator.
Yes. Berkelium has no stable isotope — every one of its nuclei decays. It does not occur in usable quantities in nature and must be synthesised.