Bohrium

Bohrium (pronEng|ˈbɔəriəm) is a chemical element in the periodic table that has the symbol Bh and atomic number 107.It is a synthetic element whose most stable isotope, Bh-270, has a half-life of 61 seconds. Chemical experiments confirmed bohrium's predicted position as a member of group 7 of the periodic table, as a heavier homologue to rhenium. [http://www.gsi.de/informationen/wti/library/scientificreport2000/Chemistry/9/r_eichler_jb2000.pdf "GAS CHEMICAL INVESTIGATION OF BOHRIUM (Bh, ELEMENT 107)"] , Eichler et al., "GSI Annual Report 2000". Retrieved on 2008-02-29]

Official discovery

The first convincing synthesis was in 1981 by a German research team led by Peter Armbruster and Gottfried Münzenberg at the Gesellschaft für Schwerionenforschung (Institute for Heavy Ion Research) in Darmstadt using the Dubna reaction.

:$,\; ^\{209\}\_\{83\}mathrm\{Bi\}\; +\; ,\; ^\{54\}\_\{24\}mathrm\{Cr\}\; ,\; o\; ,\; ^\{262\}\_\{107\}mathrm\{Bh\}\; +\; ,\; ^\{1\}\_\{0\}mathrm\{n\}$

In 1989, the GSI team successfully repeated the reaction during their efforts to measure an excitation function. During these experiments, ²⁶¹Bh was also identified in the 2n evaporation channel and it was confirmed that ²⁶²Bh exists as two isomers.

The IUPAC/IUPAP Transfermium Working Group (TWG) report in 1992 officially recognised the GSI team as discoverers of element 107.

Proposed names

Historically element 107 has been referred to as eka-rhenium.

The Germans suggested the name "nielsbohrium" with symbol "Ns" to honor the Danish physicist Niels Bohr. The Soviets had suggested this name be given to element 105 (dubnium) and the German team wished to recognise both Bohr and the fact that the Dubna team had been the first to propose the cold fusion reaction.

There was an element naming controversy as to what the elements from 101 to 109 were to be called; thus IUPAC adopted "unnilseptium" (pronEng|ˌjuːnɪlˈsɛptiəm or IPA|/ˌʌnɪlˈsɛptiəm/, symbol "Uns") as a temporary, systematic element name for this element. In 1994 a committee of IUPAC rejected the name "nielsbohrium" since there was no precedence for using a scientist's complete name in the naming of an element and thus recommended that element 107 be named "bohrium". [http://www.iupac.org/publications/pac/1994/pdf/6612x2419.pdf (IUPAC 1994 recomm)] This was opposed by the discoverers who were adamant that they had the right to name the element. The matter was handed to the Danish branch of IUPAC who voted in favour of the name "bohrium". There was some concern however that the name might be confused with boron and in particular the distinguishing of the names of their respective oxo-ions bohrate and borate. Despite this, the name "bohrium" for element 107 was recognized internationally in 1997. [http://www.iupac.org/publications/pac/1997/pdf/6912x2471.pdf (IUPAC 1997 recomm)] The IUPAC subsequently decided that bohrium salts should be called bohriates.

Electronic structure

Bohrium is element 107 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 13, 2

Quantum mechanical model: 1s²2s²2p⁶3s²3p⁶4s²3d¹⁰4p⁶5s²4d¹⁰5p⁶6s²4f¹⁴5d¹⁰6p⁶7s²5f¹⁴6d⁵

Extrapolated chemical properties of eka-rhenium/dvi-technetium

Oxidation states

Element 107 is projected to be the fourth member of the 6d series of transition metals and the heaviest member of group VII in the Periodic Table, below manganese, technetium and rhenium.All the members of the group readily portray their group oxidation state of +VII and the state becomes more stable as the group is descended. Thus bohrium is expected to form a stable +VII state.Technetium also shows a stable +IV state whilst rhenium portrays stable +IV and +III states. Bohrium may therefore show these lower states as well.

Chemistry

The heavier members of the group are known to form volatile heptoxides M₂O₇, so bohrium should also form the volatile oxide Bh₂O₇. The oxide should dissolve in water to form perbohric acid, HBhO₄.Rhenium and technetium form a range of oxyhalides from the halogenation of the oxide. The chlorination of the oxide forms the oxychlorides MO₃Cl, so BhO₃Cl should be formed in this reaction. Fluorination results in MO₃F and MO₂F₃ for the heavier elements in addition to the rhenium compounds ReOF₅ and ReF₇. Therefore, oxyfluoride formation for bohrium may help to indicate eka-rhenium properties.

Industrial and commercial use

Like seaborgium and hassium, its neighbours, bohrium has no industrial or commercial use due to its extremely short half-life. Few atoms have ever been made, but if enough were found in one area, bohrium would constitute a radiation hazard. [http://www.nrc-cnrc.gc.ca/eng/education/elements/el/bh.html]

Experimental chemistry

Gas phase chemistry

In 2000, a team at the PSI conducted a chemistry reaction using atoms of ²⁶⁷Bh produced in the reaction between Bk-249 and Ne-22 ions. The resulting atoms were thermalised and reacted with a HCl/O₂ mixture to form a volatile oxychloride. The reaction also produced isotopes of its lighter homologues, technetium (as ¹⁰⁸Tc) and rhenium (as ¹⁶⁹Re). The isothermal adsorption curves were measured and gave strong evidence for the formation of a volatile oxychloride with properties similar to that of rhenium oxychloride. This placed bohrium as a typical member of group 7.

:$mathrm\{Bh\}\; +\; frac\{3\}\{2\}cdotmathrm\{O\}\_\{2\}\; +\; mathrm\{HCl\}\; o\; mathrm\{BhO\}\_\{3\}mathrm\{Cl\}\; +\; mathrm\{H\}$

ummary of compounds

Isomerism in bohrium nuclides

²⁶²Bh

The only confirmed example of isomerism in bohrium is for the isotope ²⁶²Bh. Direct production populates two states, a ground state and an isomeric state. The ground state is confirmed as decaying by alpha emission with alpha lines at 10.08,9.82 and 9.76 MeV with a revised half life of 84 ms. The excited state decays by alpha emission with lines at 10.37 and 10.24 MeV with a revised half-life of 9.6 ms.

Chemical yields of isotopes

Cold Fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing bohrium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

Hot Fusion

The table below provides cross-sections and excitation energies for hot fusion reactions producing bohrium isotopes directly. Data in bold represents maxima derived from excitation function measurements. + represents an observed exit channel.

References

External links

* [http://www.webelements.com/webelements/elements/text/Bh/index.html WebElements.com - Bohrium]
* [http://www.apsidium.com/elements/107.htm Apsidium - Bohrium]
* [http://periodic.lanl.gov/elements/107.html Los Alamos National Laboratory - Bohrium]
* [http://bh-bohrium.info/properties.html Properties of BhO₃Cl]