What is Berkelium?
Berkelium is a chemical element with atomic number 97 and symbol Bk. This transuranic chemical element is radioactive in nature. It was the fifth transuranium element discovered after curium, americium, plutonium, and neptunium. This chemical element is a member of the actinide and transuranium element series of the periodic table of elements. Bk element belongs to the period 7th and F-block of the periodic table. This metal remains in the solid-state at standard temperature and pressure. The atomic mass of this radioactive metal is 247. The electronic configuration of berkelium is [Rn] 5f97s2. The basic details of this chemical element are as follows.
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The above image shows the position of berkelium in the periodic table.
Discovery
Berkelium was first synthesized at the University of California, Berkeley (United States)in Dec 1949. Glenn T. Seaborg, Kenneth Street, Jr., Stanley G Thompson, and Albert Ghiorso first produced this radioactive metal. The team at the University of California used a 60-inch cyclotron for this experiment. First of all, these scientists coated the americium nitrate solution on a platinum foil. Then, they evaporated this solution to convert the residue in americium dioxide by annealing. Finally, their team irradiated the target in the 60-inch cyclotron with alpha particles for 6 hours. This experiment leads to the formation of the Berkelium-243 isotope along with two free neutrons.
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The IUPAC officially declared the name of this element as berkelium after the state of its discovery, Berkeley.
Occurrence
The half-lives of all the known isotopes of berkelium are too short. Hence, no primordial berkelium could not have survived by now from the formation of the earth. Bk is present on earth’s surface only in some areas mostly at the sites of nuclear incidents. The place where the individuals did the testing of atmospheric nuclear weapons between 1945 to 1980 also contains this element. The place where the first U.S. tested the first hydrogen bomb comprises high concentrations of several actinides including berkelium. Nuclear reactors also produce this radioactive element during the process.
Properties of Berkelium
Berkelium is a soft metal that is silvery-white in color. This radioactive metal is present below the lanthanide terbium with which it shares its many characteristics. The density of this chemical element is 14.78g/cm3 whose value lies between that of curium and californium. Similarly, the melting point of this metal is 986oC which is higher than curium but less than californium. The bulk modulus of Bk is 20 GPa which is one of the lowest among the actinides. This chemical element behaves as a paramagnetic material between 70 K and room temperature. A neutral atom of Bk has an ionization potential of around 6.23eV.
Bk dissolves in several aqueous inorganic acids like all actinides to liberate hydrogen gas. The most stable oxidation state of this metal is the trivalent oxidation state (+3) mostly in aqueous solutions. The other known oxidation states of berkelium compounds are divalent (+2) and tetravalent (+4) ones. There is still uncertainty about the presence of divalent berkelium salts.
At room temperature, the reaction of berkelium with oxygen doesn't take place because of the formation of the protective oxide layer surface. However, Bk can react with molten metals, chalcogens, halogen, hydrogen to form several binary compounds. In most of the acids, the Bk3+ ions are present in green colour. In sulphuric acid, the colour of Bk4+ atoms is orange-yellow, whereas it is yellow in hydrochloric acid.
Isotopes of Berkelium
At present, researchers have found about 20 isotopes of berkelium. The mass number of these isotopes ranges from 233 to 253 (except 235, 237, and 239) in which six are nuclear isotopes. All of the known isotopes of berkelium are radioactive whose half-lives range from microseconds to several days. 247Bk has the longest half-lives among all known isotopes of Bk, which is around 1380 years. The other known isotopes of Bk with long half-lives are 248Bk and 249Bk. The half-life of 248Bk is around 300 years, and 249Bk has a half-life of about 330 days.
249Bk is the easiest to synthesise isotope of the Bk element. The soft β-particles emitted by this isotope are inconvenient for detection. It also emits alpha radiation which is weak as compared to the β-radiation. However, this radiation can be useful in the detection of this isotope. The second most crucial isotope of this radioactive metal is 247Bk. It is also an alpha-particle emitter like the isotopes of most of the actinides.
FAQs on Berkelium
1. What are the key physical and chemical properties of Berkelium?
Berkelium is a soft, silvery-white, radioactive metal belonging to the actinide series. Its key properties include:
- State: Solid at standard temperature and pressure.
- Density: 14.78 g/cm³, which is intermediate between its neighbours, curium and californium.
- Melting Point: 986°C.
- Oxidation States: The most stable oxidation state is +3, which typically forms green-coloured ions in solutions. A less stable +4 state is also known.
- Reactivity: It dissolves in various aqueous inorganic acids. While it is relatively unreactive with oxygen at room temperature due to a protective oxide layer, it can react with molten metals, halogens, and chalcogens.
2. How is Berkelium produced, and why is it so rare?
Berkelium does not occur naturally on Earth in any significant quantity. It is an artificial element produced in minute amounts inside specialized nuclear reactors or particle accelerators. The primary reason for its extreme rarity is the instability of its isotopes. The longest-living isotope, 247Bk, has a half-life of only 1,380 years. This means any primordial Berkelium that may have existed when the Earth was formed has long since decayed into other elements. It is only found today in trace amounts at nuclear weapons test sites or produced for research.
3. What are the main uses of Berkelium?
Due to its extreme rarity, high radioactivity, and the difficulty in producing it, Berkelium has no commercial or industrial applications. Its use is confined entirely to basic scientific research. Specifically, it is used as a target material to synthesise even heavier, superheavy elements. For example, the isotope 249Bk was instrumental in the first synthesis of Tennessine (element 117). It also serves as a source for producing the isotope Californium-249 for further study.
4. What are the most significant isotopes of Berkelium, and why is their half-life important?
While about 20 isotopes of Berkelium are known, two are particularly significant for research:
- 249Bk: This is the most accessible isotope as it is easiest to synthesise in weighable quantities. It has a half-life of about 330 days. Its availability makes it the primary choice for studying Berkelium's chemistry and for use as a target for creating new elements.
- 247Bk: This is the most stable isotope, with a long half-life of 1,380 years. However, it is much more difficult to produce.
The short half-lives of all Berkelium isotopes are a major challenge, as they decay relatively quickly, making it difficult to accumulate enough material for extensive or prolonged experiments.
5. What does Berkelium's position in the actinide series tell us about its chemical behaviour?
Berkelium's position as an f-block element in the actinide series provides important clues about its properties. Like other actinides, it is a heavy, radioactive metal. Its electron configuration, [Rn] 5f⁹7s², leads to complex chemical behaviour with multiple oxidation states, a hallmark of actinides. The stability of its +3 oxidation state is a characteristic shared with its lanthanide counterpart, Terbium, and other later actinides. Its placement correctly predicts its metallic character and its ability to form various binary compounds.
6. Are there any health risks associated with Berkelium?
Yes, as a radioactive element, Berkelium is considered a significant health hazard, although its effects are not widely studied due to its rarity. If ingested or inhaled, it tends to accumulate in the skeletal system. The radiation it emits can damage surrounding tissues, interfere with the production of red blood cells, and increase the risk of cancer. Furthermore, its decay products, such as Californium-249, are also highly radioactive and dangerous.
7. Why was element 97 named Berkelium, and what is the significance of its discovery?
Element 97 was named Berkelium (Bk) in honour of Berkeley, California, the location of the University of California Radiation Laboratory where it was first synthesised in 1949. This naming followed a tradition of honouring places significant to an element's discovery. The creation of Berkelium was a major step in nuclear science, as it was the fifth transuranic element synthesised, pushing the boundaries of the known periodic table and allowing scientists to study the properties of extremely heavy atomic nuclei.
