Bohrium

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Not to be confused with Borium.

Bohrium, 107Bh
Bohrium
Pronunciation/ˈbɔːriəm/ ⓘ ​(BOR-ee-əm)
Mass number[270] (unconfirmed: 278)
Bohrium in the periodic table
Hydrogen Helium
Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon
Sodium Magnesium Aluminium Silicon Phosphorus Sulfur Chlorine Argon
Potassium Calcium Scandium Titanium Vanadium Chromium Manganese Iron Cobalt Nickel Copper Zinc Gallium Germanium Arsenic Selenium Bromine Krypton
Rubidium Strontium Yttrium Zirconium Niobium Molybdenum Technetium Ruthenium Rhodium Palladium Silver Cadmium Indium Tin Antimony Tellurium Iodine Xenon
Caesium Barium Lanthanum Cerium Praseodymium Neodymium Promethium Samarium Europium Gadolinium Terbium Dysprosium Holmium Erbium Thulium Ytterbium Lutetium Hafnium Tantalum Tungsten Rhenium Osmium Iridium Platinum Gold Mercury (element) Thallium Lead Bismuth Polonium Astatine Radon
Francium Radium Actinium Thorium Protactinium Uranium Neptunium Plutonium Americium Curium Berkelium Californium Einsteinium Fermium Mendelevium Nobelium Lawrencium Rutherfordium Dubnium Seaborgium Bohrium Hassium Meitnerium Darmstadtium Roentgenium Copernicium Nihonium Flerovium Moscovium Livermorium Tennessine Oganesson
Re
↑
Bh
↓
(Uhu)
seaborgium ← bohrium → hassium
Atomic number (Z)107
Groupgroup 7
Periodperiod 7
Block  d-block
Electron configuration[Rn] 5f14 6d5 7s2[1][2]
Electrons per shell2, 8, 18, 32, 32, 13, 2
Physical properties
Phase at STPsolid (predicted)[3]
Density (near r.t.)26–27 g/cm3 (predicted)[4][5]
Atomic properties
Oxidation states(+3), (+4), (+5), +7[2][6] (parenthesized: prediction)
Ionization energies
  • 1st: 740 kJ/mol
  • 2nd: 1690 kJ/mol
  • 3rd: 2570 kJ/mol
  • (more) (all but first estimated)[2]
Atomic radiusempirical: 128 pm (predicted)[2]
Covalent radius141 pm (estimated)[7]
Other properties
Natural occurrencesynthetic
Crystal structure ​hexagonal close-packed (hcp)
Hexagonal close-packed crystal structure for bohrium

(predicted)[3]
CAS Number54037-14-8
History
Namingafter Niels Bohr
DiscoveryGesellschaft für Schwerionenforschung (1981)
Isotopes of bohrium
Main isotopes[8] Decay
abun­dance half-life (t1/2) mode pro­duct
267Bh synth 17 s α 263Db
270Bh synth 2.4 min α 266Db
271Bh synth 2.9 s[9] α 267Db
272Bh synth 8.8 s α 268Db
274Bh synth 40 s[10] α 270Db
278Bh synth 11.5 min?[11] SF –
 Category: Bohrium
| references

Bohrium is a chemical element with symbol Bh and atomic number 107. It is named after Danish physicist Niels Bohr. It is a synthetic element (an element that can be created in a laboratory but is not found in nature) and radioactive; the most stable known isotope, 270Bh, has a half-life of approximately 61 seconds, though the unconfirmed 278Bh may have a longer half-life of about 690 seconds.

In the periodic table of the elements, it is a d-block transactinide element. It is a member of the 7th period and belongs to the group 7 elements as the fifth member of the 6d series of transition metals. Chemistry experiments have confirmed that bohrium behaves as the heavier homologue to rhenium in group 7. The chemical properties of bohrium are characterized only partly, but they compare well with the chemistry of the other group 7 elements.

History

Element 107 was originally proposed to be named after Niels Bohr, a Danish nuclear physicist, with the name nielsbohrium (Ns). This name was later changed by IUPAC to bohrium (Bh).

Discovery

Two groups claimed discovery of the element. Evidence of bohrium was first reported in 1976 by a Russian research team led by Yuri Oganessian, in which targets of bismuth-209 and lead-208 were bombarded with accelerated nuclei of chromium-54 and manganese-55 respectively.[12] Two activities, one with a half-life of one to two milliseconds, and the other with an approximately five-second half-life, were seen. Since the ratio of the intensities of these two activities was constant throughout the experiment, it was proposed that the first was from the isotope bohrium-261 and that the second was from its daughter dubnium-257. Later, the dubnium isotope was corrected to dubnium-258, which indeed has a five-second half-life (dubnium-257 has a one-second half-life); however, the half-life observed for its parent is much shorter than the half-lives later observed in the definitive discovery of bohrium at Darmstadt in 1981. The IUPAC/IUPAP Transfermium Working Group (TWG) concluded that while dubnium-258 was probably seen in this experiment, the evidence for the production of its parent bohrium-262 was not convincing enough.[13]

In 1981, a German research team led by Peter Armbruster and Gottfried Münzenberg at the GSI Helmholtz Centre for Heavy Ion Research (GSI Helmholtzzentrum für Schwerionenforschung) in Darmstadt bombarded a target of bismuth-209 with accelerated nuclei of chromium-54 to produce 5 atoms of the isotope bohrium-262:[14]

209
83Bi
 + 54
24Cr
 → 262
107Bh
 +
n

This discovery was further substantiated by their detailed measurements of the alpha decay chain of the produced bohrium atoms to previously known isotopes of fermium and californium. The IUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report.[13]

Proposed names

The German group suggested the name nielsbohrium with symbol Ns to honor the Danish physicist Niels Bohr. The Soviet scientists at the Joint Institute for Nuclear Research in Dubna, Russia had suggested this name be given to element 105 (which was finally called 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 to solve the controversial problem of the naming of element 105. The Dubna team agreed with the German group's naming proposal for element 107.[15]

There was an element naming controversy as to what the elements from 104 to 106 were to be called; the IUPAC adopted unnilseptium (symbol Uns) as a temporary, systematic element name for this element.[16] In 1994 a committee of IUPAC recommended that element 107 be named bohrium, not nielsbohrium, since there was no precedence for using a scientist's complete name in the naming of an element.[16][17] This was opposed by the discoverers as there was some concern that the name might be confused with boron and in particular the distinguishing of the names of their respective oxyanions, bohrate and borate. The matter was handed to the Danish branch of IUPAC which, despite this, voted in favour of the name bohrium, and thus the name bohrium for element 107 was recognized internationally in 1997.[16] It was subsequently decided that oxyanions of bohrium should be called bohriates to avoid confusion.[18]

Isotopes

Main article: Isotopes of bohrium
List of bohrium isotopes
Isotope
 Half-life
[19][20]		 Decay
mode[19][20]		 Discovery
year		 Reaction
260Bh 35 ms α 2007 209Bi(52Cr,n)[21]
261Bh 11.8 ms α 1986 209Bi(54Cr,2n)[22]
262Bh 84 ms α 1981 209Bi(54Cr,n)[14]
262mBh 9.6 ms α 1981 209Bi(54Cr,n)[14]
263Bh 0.2? ms α ? unknown —
264Bh 0.97 s α 1994 272Rg(—,2α)[23]
265Bh 0.9 s α 2004 243Am(26Mg,4n)[24]
266Bh 0.9 s α 2000 249Bk(22Ne,5n)[25]
267Bh 17 s α 2000 249Bk(22Ne,4n)[25]
268Bh 25? s α, SF? unknown —
269Bh 25? s α ? unknown —
270Bh 61 s α 2006 282Nh(—,3α)[26]
271Bh 1.2 s α 2003 287Mc(—,4α)[26]
272Bh 9.8 s α 2005 288Mc(—,4α)[26]
273Bh 90? min α, SF ? unknown —
274Bh ~54 s α 2009 294Ts(—,5α)[10]
275Bh 40? min SF ? unknown —
276Bh — — unknown —
277Bh — — unknown —
278Bh 690 s? SF 1998? 290Fl(e−,νe3α)?

Bohrium has no stable or naturally occurring isotopes. Several radioactive isotopes have been synthesized in the laboratory, either by fusing two atoms or by observing the decay of heavier elements. Twelve different isotopes of bohrium have been reported with atomic masses 260–262, 264–267, 270–272, 274, and 278, one of which, bohrium-262, has a known metastable state. All of these but the unconfirmed 278Bh decay only through alpha decay, although some unknown bohrium isotopes are predicted to undergo spontaneous fission.[19]

The lighter isotopes usually have shorter half-lives; half-lives of under 100 ms for 260Bh, 261Bh, 262Bh, and 262mBh were observed. 264Bh, 265Bh, 266Bh, and 271Bh are more stable at around 1 s, and 267Bh and 272Bh have half-lives of about 10 s. The heaviest isotopes are the most stable, with 270Bh and 274Bh having measured half-lives of about 61 s and 54 s respectively, and the even heavier unconfirmed isotope 278Bh appearing to have an even longer half-life of about 690 s. The unknown isotopes 273Bh and 275Bh are predicted to have even longer half-lives of around 90 minutes and 40 minutes respectively. Before its discovery, 274Bh was also predicted to have a long half-life of 90 minutes, but it was found to have a shorter half-life of only about 54 seconds.[19]

The proton-rich isotopes with masses 260, 261, and 262 were directly produced by cold fusion, those with mass 262 and 264 were reported in the decay chains of meitnerium and roentgenium, while the neutron-rich isotopes with masses 265, 266, 267 were created in irradiations of actinide targets. The five most neutron-rich ones with masses 270, 271, 272, 274, and 278 (unconfirmed) appear in the decay chains of 282Nh, 287Mc, 288Mc, 294Ts, and 290Fl respectively. These eleven isotopes have half-lives ranging from about ten milliseconds for 262mBh to about one minute for 270Bh and 274Bh, extending to about twelve minutes for the unconfirmed 278Bh, one of the longest-lived known superheavy nuclides.[27]

Predicted properties

Chemical

Bohrium is the fifth member of the 6d series of transition metals and the heaviest member of group 7 in the periodic table, below manganese, technetium and rhenium. All the members of the group readily portray their group oxidation state of +7 and the state becomes more stable as the group is descended. Thus bohrium is expected to form a stable +7 state. Technetium also shows a stable +4 state whilst rhenium exhibits stable +4 and +3 states. Bohrium may therefore show these lower states as well.[28] The higher +7 oxidation state is more likely to exist in oxyanions, such as perbohriate, BhO−
4, analogous to the lighter permanganate, pertechnetate, and perrhenate. Nevertheless, bohrium(VII) is likely to be unstable in aqueous solution, and would probably be easily reduced to the more stable bohrium(IV).[2]

Technetium and rhenium are known to form volatile heptoxides M2O7 (M = Tc, Re), 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.[29] Since the oxychlorides are asymmetrical, and they should have increasingly large dipole moments going down the group, they should become less volatile in the order TcO3Cl > ReO3Cl > BhO3Cl: this was experimentally confirmed in 2000 by measuring the enthalpies of adsorption of these three compounds. The values are for TcO3Cl and ReO3Cl are −51 kJ/mol and −61 kJ/mol respectively; the experimental value for BhO3Cl is −77.8 kJ/mol, very close to the theoretically expected value of −78.5 kJ/mol.[2]

Physical and atomic

Bohrium is expected to be a solid under normal conditions and assume a hexagonal close-packed crystal structure (c/a = 1.62), similar to its lighter congener rhenium.[3] It should be a very heavy metal with a density of around 37.1 g/cm3, which would be the third-highest of any of the 118 known elements, lower than only meitnerium (37.4 g/cm3) and hassium (41 g/cm3), the two following elements in the periodic table. In comparison, the densest known element that has had its density measured, osmium, has a density of only 22.61 g/cm3. This results from bohrium's high atomic weight, the lanthanide and actinide contractions, and relativistic effects, although production of enough bohrium to measure this quantity would be impractical, and the sample would quickly decay.[2]

The atomic radius of bohrium is expected to be around 128 pm.[2] Due to the relativistic stabilization of the 7s orbital and destabilization of the 6d orbital, the Bh+ ion is predicted to have an electron configuration of [Rn] 5f14 6d4 7s2, giving up a 6d electron instead of a 7s electron, which is the opposite of the behavior of its lighter homologues manganese and technetium. Rhenium, on the other hand, follows its heavier congener bohrium in giving up a 5d electron before a 6s electron, as relativistic effects have become significant by the sixth period, where they cause among other things the yellow color of gold and the low melting point of mercury. The Bh2+ ion is expected to have an electron configuration of [Rn] 5f14 6d3 7s2; in contrast, the Re2+ ion is expected to have a [Xe] 4f14 5d5 configuration, this time analogous to manganese and technetium.[2] The ionic radius of hexacoordinate heptavalent bohrium is expected to be 58 pm (heptavalent manganese, technetium, and rhenium having values of 46, 57, and 53 pm respectively). Pentavalent bohrium should have a larger ionic radius of 83 pm.[2]

Experimental chemistry

In 1995, the first report on attempted isolation of the element was unsuccessful, prompting new theoretical studies to investigate how best to investigate bohrium (using its lighter homologs technetium and rhenium for comparison) and removing unwanted contaminating elements such as the trivalent actinides, the group 5 elements, and polonium.[30]

In 2000, it was confirmed that although relativistic effects are important, bohrium behaves like a typical group 7 element.[31] A team at the Paul Scherrer Institute (PSI) conducted a chemistry reaction using six atoms of 267Bh produced in the reaction between 249Bk and 22Ne 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.[32] The adsorption enthalpies of the oxychlorides of technetium, rhenium, and bohrium were measured in this experiment, agreeing very well with the theoretical predictions and implying a sequence of decreasing oxychloride volatility down group 7 of TcO3Cl > ReO3Cl > BhO3Cl.[2]

2 Bh + 3 O
2 + 2 HCl → 2 BhO
3Cl + H
2

References

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  21. ^ Nelson, S.; Gregorich, K.; Dragojević, I.; Garcia, M.; Gates, J.; Sudowe, R.; Nitsche, H. (2008). "Lightest Isotope of Bh Produced via the Bi209(Cr52,n)Bh260 Reaction". Physical Review Letters. 100 (2): 022501. Bibcode:2008PhRvL.100b2501N. doi:10.1103/PhysRevLett.100.022501. PMID 18232860.
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  24. ^ Gan, Z.G.; Guo, J. S.; Wu, X. L.; Qin, Z.; Fan, H. M.; Lei, X. G.; Liu, H. Y.; Guo, B.; Xu, H. G. (2004). "New isotope 265Bh". The European Physical Journal A. 20 (3): 385. Bibcode:2004EPJA...20..385G. doi:10.1140/epja/i2004-10020-2. {{cite journal}}: Unknown parameter |displayauthors= ignored (|display-authors= suggested) (help)
  25. ^ a b Wilk, P. A.; Gregorich, K. E.; Turler, A.; Laue, C. A.; Eichler, R.; Ninov V, V.; Adams, J. L.; Kirbach, U. W.; Lane, M. R. (2000). "Evidence for New Isotopes of Element 107: 266Bh and 267Bh". Physical Review Letters. 85 (13): 2697–700. Bibcode:2000PhRvL..85.2697W. doi:10.1103/PhysRevLett.85.2697. PMID 10991211. {{cite journal}}: Unknown parameter |displayauthors= ignored (|display-authors= suggested) (help)
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  28. ^ Cite error: The named reference BFricke was invoked but never defined (see the help page).
  29. ^ Hans Georg Nadler "Rhenium and Rhenium Compounds" Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000. doi:10.1002/14356007.a23_199
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  31. ^ Gäggeler, H. W.; Eichler, R.; Brüchle, W.; Dressler, R.; Düllmann, Ch. E.; Eichler, B.; Gregorich, K. E.; Hoffman, D. C.; Hübener, S. (2000). "Chemical characterization of bohrium (element 107)". Nature. 407 (6800): 63–5. doi:10.1038/35024044. PMID 10993071. {{cite journal}}: Unknown parameter |displayauthors= ignored (|display-authors= suggested) (help)
  32. ^ Eichler; et al. "Gas chemical investigation of bohrium (Bh, element 107)" (PDF). GSI Annual Report 2000. Archived from the original (PDF) on 2012-02-19. Retrieved 2008-02-29. {{cite web}}: Explicit use of et al. in: |author= (help)

External links

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