Berkelium (Bk)

Berkelium is a chemical element with the symbol Bk and the atomic number 97 in the periodic table of elements. Since it’s synthesized in a laboratory, berkelium is not found naturally in its elemental form in Earth’s crust. Being a member of the actinide family of periodic table elements, this radioactive metal shares the physical and chemical properties with all the actinide elements of the group.

Fact Box

Chemical and Physical Properties of Berkelium

The symbol in the periodic table of elements: 

Atomic number: 97

Atomic weight (mass): 247.00 g.mol -1

Group: 3 (Actinides)

Period: 7

Color: Silvery-white

Physical state: Solid (and relatively soft) metal at room temperature of 20C

Half-life: 4.5 hours

Electronegativity according to Pauling: 1.30

Density: 14.78 at room temperature of 20°.C

Melting point: 986°C, 1807°F, 1259 K

Boiling point: 2627 °C

Van der Waals radius: 244 pm

Ionic radius: 0.949Å

Isotopes: 14

Most characteristic isotope: 247Bk, 249Bk 

Electronic shell: [Rn] 5f97s2

The energy of the first ionization: 

The energy of the second ionization: 

Discovery date: In 1949 by Glenn. T. Seaborg, Albert Ghiorso, Stanley G. Thompson, and Kenneth Street, Jr.

Berkelium is a man-made radioactive metal that shares the chemical and physical properties with the neighbouring chemical elements californium (Cf) and curium (Cm). With the periodic table symbol Bk, atomic number 97, atomic mass of 247.00 g.mol -1, and density of 14.78 at 20°.C, berkelium is a relatively soft metal that can be diluted in aqueous inorganic acids. This reaction, in turn, releases gaseous hydrogen.  

It has an electronegativity of 1.30 according to Pauling, and an electron configuration of Rn 5f9 7s2, whereas the atomic radius according to van der Waals is 244 pm. This transuranic chemical element is reactive with other chemical elements, and mostly resembles the malleable and ductile rare earth element terbium (Tb). 

The actinoide metals, such as curium, berkelium, and californium, share the same crystal structure with berkelium. Hence, this radioactive metal can occur as a double hexagonal, closest packed, and face centered cubic crystal.

How Was Berkelium Discovered?

This radioactive element was produced in 1949, at the University of California, Berkeley, California, USA. In an effort to better understand the chemical and physical properties of the transuranium elements, Glenn T. Seaborg, Albert Ghiorso, Stanley G. Thompson, and Kenneth Street, Jr. attempted to make a new chemical element by bombarding (i.e. induced radioactivity) the americium-241 isotope (produced in 1944) with alpha particles in an 60-inch cyclotron accelerator, triggering an ion exchange. The resulting electron-capture activity in this scientific trial was the production of isotope of the new element berkelium, the 243Bk. 

How Did Berkelium Get Its Name?

Berkelium (Bk) was named after the city of Berkeley, California, where the scientific experiment that produces the pure form of berkelium was first conducted. On the other hand, the University of Berkeley that housed the laboratories where this research in the realms of chemistry took place back in 1949, was named after the Anglo-Irish philosopher and scientist, Bishop George Berkeley. His greatest contribution to the world of science is his Theory of idealism that denies materialism and gives way to perception and thought. 

Where Can You Find Berkelium?

SInce it cannot be found in Earth’s crust, microgram quantities of this powerful radioactive chemical substance are produced in nuclear reactors for scientific purposes.  

Berkelium in Everyday Life

Due to its rarity as a radioactive man-made chemical element, berkelium does not have any commercial use or practical applications in real life. This transuranium element is mainly used for scientific research, as a target for synthesizing of heavier chemical elements. 

How Dangerous Is Berkelium?

Similar to the other chemical elements from the family of actinides in the periodic table, berkelium has a tendency to remain longest in the lungs and the bones upon accumulation. In comparison to the radioactive effects of the other actinides, berkelium is not so hazardous by itself due to its short half-life. However, after the expiration of its half-life, berkelium-249 decays into the more significantly radioactive californium-249 that imposes a much greater risk of radiation and toxicity. 

Environmental Effects of Berkelium

The environmental effects of berkelium are rarely considered due to the fact that this is an element that does not occur in its elemental form in nature. On the other hand, the quantities of berkelium that are produced in chemical laboratories are extremely small. 

This fact shifts the focus to the environments where this actinide is produced, such as nuclear facilities, where the danger of exposure to berkelium’s radioactivity is the biggest and imposes an extreme health hazard. The same holds true for the locations that have been affected by exposure to the radioactivity of other radioactive chemical elements. 

Namely, berkelium still ends up being one of the radioactive man-made metals in the periodic system of elements, making it a hazardous substance. Its radioactive properties can be recognized in locations where nuclear testings are conducted or a nuclear disaster has occured. 

The Hydrogen Bomb of the U.S. Army 

The Eniwetok Atoll in the Pacific is the location where the first nuclear weapon of the U.S. army was tested. The thermonuclear bomb, more familiar as the ‘hydrogen bomb’, held 1000 times more power than the atomic bomb. In 1952, it was dropped from the nowadays iconic American B52 jet bomber. After the nuclear testing, traces of berkelium were found in the locations where the effects of the hydrogen bomb were felt. 

The Nuclear Accident in the Chernobyl Power Plant

In 1986, Ukraine became the location of the biggest nuclear accident in history. Upon an explosion of a nuclear reactor, there was widespread radiation triggered by the release of radioactive elements. Since radium, berkelium, plutonium, strontium, and caesium were used in the operation of this power plant, these radioactive elements saturated the air, covering enormous territories.

The entire site was devastated by radiation, including the local wildlife and nature. Moreover, the hazardous effects of the radioactive components emitted after the explosion of the Chernobyl nuclear power plant affected not only the neighbouring countries of Ukraine, but also a large part of Europe. 

What Is Radioactivity and What Are Its Health Hazards?

The radioactive atoms of a chemical element characterize an unstable nucleus. This instability occurs due to an imbalance between the number of neutrons and protons. When the scientists add protons or neutrons to a nucleus of an atom, they trigger its instability and the decay process of the element’s isotope. At this point, the atom tries to release the unnecessary protons, neutrons, or positrons, via alpha, beta, or gamma decay mode.

These radioactive modes of nucleus decay radiate ionizing radiation in the surrounding environment, which imposes an extreme health hazard. The exposure to radiation can lead to some severe and incurable diseases, as well as cancer on all tissues and organs of the body. 

Isotopes of Berkelium

There are 18 unstable isotopes of berkelium with a mass number that ranges from 233Bk to 253Bk. All isotopes of this member of the actinide family of the periodic system are radioactive. Having a half-life of 1,380 years, 247Bk is the longest living and most stable isotope of berkelium. The berkelium-249 isotope decays into californium-249 and can be most easily reproduced.  

The following is a tabular presentation of the berkelium isotopes, their decay mode, and half-life.



[n 1]

ZNIsotopic mass (Da)


[n 2][n 3]




[n 4]




Spin and



[n 5][n 6]

Excitation energy[n 6]
233Bk[2]97136 21 sα229Am 
234Bk[3]97137 19(+6-4) sα (50%)230Am 
β+ (50%)234Cm
236Bk97139236.05733(43)#22(+13-6) s[4]α232Am 
238Bk97141238.05828(31)#2.40(8) minα234Am 
β+, SF (.048%)(various)
β+ (rare)238Cm
240Bk97143240.05976(16)#4.8(8) minβ+ (90%)240Cm 
α (10%)236Am
β+, SF (.002%)(various)
241Bk97144241.06023(22)#4.6(4) minα237Am(7/2+)
β+ (rare)241Cm
242Bk97145242.06198(22)#7.0(13) minβ+ (99.99%)242Cm2−#
β+, SF (3×10−4%)(various)
242mBk200(200)# keV600(100) nsSF(various) 
243Bk97146243.063008(5)4.5(2) hβ+ (99.85%)243Cm(3/2−)
α (.15%)239Am
244Bk97147244.065181(16)4.35(15) hβ+ (99.99%)244Cm(4−)#
α (.006%)240Am
245Bk97148245.0663616(25)4.94(3) dEC (99.88%)245Cm3/2−
α (.12%)241Am
246Bk97149246.06867(6)1.80(2) dβ+ (99.8%)246Cm2(−)
α (.2%)242Am
247Bk97150247.070307(6)1.38(25)×103 yα243Am(3/2−)
SF (rare)(various)
248Bk97151248.07309(8)#>300 y[5]α244Am6+#
248mBk30(70)# keV23.7(2) hβ248Cf1(−)
249Bk[n 7]97152249.0749867(28)330(4) dβ249Cf7/2+
α (.00145%)245Am
SF (4.7×10−8%)(various)
249mBk8.80(10) keV300 µsIT249Bk(3/2−)
250Bk97153250.078317(4)3.212(5) hβ250Cf2−
250m1Bk35.59(5) keV29(1) µsIT250Bk(4+)
250m2Bk84.1(21) keV213(8) µs  (7+)
251Bk97154251.080760(12)55.6(11) minβ251Cf(3/2−)#
α (10−5%)247Am
251mBk35.5(13) keV58(4) µsIT251Bk(7/2+)#
252Bk97155252.08431(22)#1.8(5) minβ252Cf 
253Bk97156253.08688(39)#10# minβ253Cf 

Source: Wikipedia

List of Berkelium Compounds

The following is a list of some of the chemical compounds of berkelium:

  • Berkelium oxychloride (BkOCl);
  • Berkelium fluoride (BkF3);
  • Berkelium (II) dioxide (BkO2);
  • Berkelium (III) trioxide (BkO3).

Even though this chemical element is not thoroughly researched, many compounds have been formed with it. With oxidation states +3 and +4, berkelium mostly forms compounds with hydrogen, chalcogens, halides, halogens, and pnictides, which have been researched via X-ray diffraction applied to berkelium dioxide (BkO2).

Berkelium can also be a part of some organometallic compounds. Berkelium chloride (BkCl3) was the first compound with this radioactive synthetic metal that was produced in a slightly larger quantity. 

5 Interesting Facts and Explanations

  1. After Darmstadtium (named after the University of Darmstadt in Germany), Berkelium is the second of the only two elements named after a university. 
  2. Berkelium is the fifth man-made chemical element of the actinide series in the periodic table of elements, where it’s located after the last chemical element that occurs naturally – uranium. Other transuranium elements are neptunium, plutonium, curium, and americium
  3. The quantity of world-wide produced berkelium per year amounts to less than one gram of this radioactive substance.
  4. The first visible quantities of berkelium chloride (BkCl3) were synthesized in 1962. 
  5. Berkelium shares the same period with the following chemical elements of the periodic table: actinium, californium, copernicium, curium, darmstadtium, dubnium, francium, radium, oganesson, livermorium, thorium, protactinium, meitnerium, flerovium, uranium, neptunium, plutonium, americium, einsteinium, fermium, moscovium, mendelevium, nobelium, lawrencium, rutherfordium, seaborgium, bohrium, hassium, roentgenium, nihonium, and tennessine