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Berkelium (Bk): structure, properties, obtaining, uses

There are also small amounts dispersed in the environment for testing nuclear weapons, serious accidents in nuclear power plants such as Chernobyl and the release happens from waste from the plants of nuclear energy.

Symbol, number and atomic mass of the element berkelium. Source: me / CC BY-SA (https://creativecommons.org/licenses/by-sa/2.5). Source: Wikimedia Commons.

No practical utility has been found for berkelium, because it is produced in very small quantities and the fact that all of its isotopes (Bk atoms with different numbers of neutrons in the nucleus) are radioactive. Its main application so far has been in scientific studies.

Nomenclature

  • Berkelium, symbol Bk.
  • Berkelium-243, Bk-243 or 243 Bk: isotope of berkelium with atomic mass 243.

Discovery

Photomicrograph of 1.7 micrograms of solid metallic berkelium obtained in 1969. Oak Ridge National Laboratory, US Department of Energy / Public domain. Source: Wikimedia Commons.

It was first produced in 1949 by scientists Glen Seaborg, Stanley G. Thompson, and Al Ghiorso at California Berkeley University, when they bombarded Americium-241 with high-energy alpha particles using a cyclotron (a particle accelerator).

Immediately after irradiation the material was adequately dissolved and passed through an ion exchange resin column, using an ammonium citrate solution as eluent.

In this way, they obtained an isotope of element number 97 with an atomic mass of 243, which emits alpha particles and has a half-life of 4.5 hours.

Element name

At first, several researchers proposed that the element take the name of one of its discoverers, Glen Seaborg, since he had the merit of having managed to synthesize 10 elements in several years of work.

Appearance of an area of ​​the University of Berkeley, Califronia. Author: Sarangib. Source: Pixabay.

The name Berkeley comes from the Anglo-Irish philosopher George Barkeley, a name whose pronunciation later changed in the United States when the city and the university were founded in 1869.

That coincidentally was the year that Dmitri Mendeleev published his first periodic table and began to predict the existence of new elements such as berkelium.

Electronic structure

Its electronic configuration is:

2 ; 2 2 2 6 ; 3 2 3 6 3 10 ; 4 2 4 6 4 10 4 14 ; 5 2 5 6 5 10 ; 6 2 6 6 ; 5 9 7 2 ,

or in compact form:

[Rn] 5 9 7 2 .

Electronic structure of berkelium. You can see the orbitals and electrons. Ahazard.sciencewriter / CC BY-SA (https://creativecommons.org/licenses/by-sa/4.0). Source: Wikimedia Commons.

Obtaining

The first sample of the metal was prepared in 1969 by a reduction reaction of fluoride (BkF 3 ) with lithium metal (Li) at a temperature of 1300 K.

To prepare thin sheets of the metal, the oxide BkO 2 is reduced with thorium (Th) or lanthanum (La) metallic.

Berkelium physical properties

Physical state

Metallic solid with a silver appearance.

Berkelium metal has two crystalline forms: alpha (compact double hexagonal) and beta (face-centered cubic).

Atomic mass

247

Melting point

1050 ºC (alpha form)

986 ° C (beta form)

Boiling point

2627 ºC

Density

14.78 g / cm 3 (alpha form)

13.25 g / cm 3 (beta form)

Paramagnetism

According to some sources, certain berkelium compounds show paramagnetic properties, which means that they are attracted to magnetic fields.

This characteristic is of the paramagnetic type because when the magnetic action is suspended, the material cannot maintain such properties on its own.

Chemical properties

At elevated temperatures metallic berkelium rapidly oxidizes in air or oxygen, forming its oxides. It is easily soluble in mineral acids, releasing hydrogen gas H 2 and forming Bk 3+ ions .

Oxidation states

The initial investigations of this element were limited to ion exchange and co-precipitation experiments, with which it was possible to observe that the oxidation state +3 is stable and the +4 is accessible in aqueous solution, since Bk 3+ can be oxidized by the bromate ion (BrO  ) to give Bk 4+ .

Stabilization of Bk 4+

In 2017, the stabilization of Bk 4+ in solution was reported using the compound formed by hydroxypyridinone groups attached to a polyamine structure (called 3,4,3-LI (1,2-HOPO) ligand).

This compound has eight places where the ion binds, which correspond to the oxygen atoms of the C = O and N-OH groups, leaving the Bk 4+ firmly bound to the ligand, remaining stable.

Solid compounds

Bk 4+ can coprecipitate with cerium (Ce 4+ ) or zirconium (Zr 4+ ) in the form of phosphate or iodate. It can also be extracted into hexane solutions of bis (2-ethylhexyl) hydrogen phosphate or other similar complexing agent.

The first berkelium compound to be produced in visible quantities was chloride (BkCl 3 ), from which 0.000000003 grams were obtained in 1962. Since then, several berkelium compounds have been prepared and studied.

Examples include phosphate (BkPO 4 ), oxychloride (BkOCl), fluorides (BkF 3 and BkF 4 ), dioxide (BkO 2 ), trioxide (Bk 2 O 3 ), iodates (Bk (IO 3 ) 3 and Bk (IO 3 ) 4 ), hydrochloride [BkCl 2 (H 2 O) 6 ] Cl, oxalate, organometallic compounds and coordination compounds, among others.

New oxidation state +5

In 2018, a group of researchers from several countries managed to produce a nitrate complex with pentavalent berkelium (Bk 5+ ) whose formula is BkO 2 (NO 3 )  , by eliminating two molecules of NO 2 from the Bk ion (NO 3 )  , (Bk 3+ ).

Computational energy calculations confirmed that the oxidation state +5 is the one with the greatest stability in this berkenyl nitrate complex, being therefore the most probable.

Isotopes

From berkelium, 14 isotopes with atomic masses from 238 to 251 have been synthesized. All are radioactive.

The most stable is berkelium-247, whose half-life is 1,380 years. Each atom of this isotope when disintegrates emits an alpha particle and forms an americium-243 atom.

Bk-249 has a half-life of 330 days, undergoes beta decay, and is converted to Californium-249.

Applications

Since only very small amounts of this element have been obtained, it is only used in basic scientific research .

In obtaining heavier elements

The Bk-249 isotope has a relatively long half-life and can be obtained in microgram quantities, which is why it is used to synthesize heavier elements by bombarding its atoms with charged particles.

Micro-amount of Bk dissolved in a test tube. It took 250 days to obtain it. You can see the protective glove against the radioactivity of this element. ORNL, Department of Energy / Public domain. Source: Wikimedia Commons.

In physicochemical studies

The investigations carried out with Bk allow more precise extrapolations about the properties and behavior of other elements that follow it in the actinide series, since the heavier elements are more difficult to obtain, have very short half-lives and are much longer. radioactive.

Risks

Berkelium is a radioactive element. The release of radioactivity in the environment can reach all species of animals and plants causing damage to them. Deterioration can accumulate in successive generations.

Nuclear power plant waste is radioactive and therefore very dangerous. Author: ar130405. Source: Pixabay.

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