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Bohrium

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Bohrium

Bohrium,  107Bh
General properties
Name, symbol bohrium, Bh
Pronunciation
Bohrium in the periodic table
Re

Bh

(Upe)
bohriumhassium
Atomic number 107
Standard atomic weight (Ar) [270]
Element category   transition metal
Group, block group 7, d-block
Period period 7
Electron configuration [Rn] 5f14 6d5 7s2 (calculated)[1][2]
per shell
2, 8, 18, 32, 32, 13, 2 (predicted)
Physical properties
Phase solid (predicted)[3]
Density near r.t. 37.1 g/cm3 (predicted)[2][4]
Atomic properties
Oxidation states 7, (5), (4), (3)[2][4] ​(parenthesized oxidation states are predictions)
Ionization energies 1st: 742.9 kJ/mol
2nd: 1688.5 kJ/mol
3rd: 2566.5 kJ/mol
(more) (all estimated)[2]
Atomic radius empirical: 128 pm (predicted)[2]
Covalent radius 141 pm (estimated)[5]
Miscellanea
Crystal structure hexagonal close-packed (hcp)
Hexagonal close-packed crystal structure for bohrium

(predicted)[3]
CAS Registry Number 54037-14-8
History
Naming after Niels Bohr
Discovery Gesellschaft für Schwerionenforschung (1981)
Most stable isotopes
iso NA half-life DM DE (MeV) DP
274Bh syn ~54 s[6] α 8.8 270Db
272Bh syn 9.8 s α 9.02 268Db
271Bh syn 1.2 s[7] α 9.35[7] 267Db
270Bh syn 61 s α 8.93 266Db
267Bh syn 17 s α 8.83 263Db

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.

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. 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).

Official discovery

Bohrium was first convincingly synthesized in 1976 by a Russian research team led by Yuri Oganessian.[8] The team bombarded a target of bismuth-209 with accelerated nuclei of chromium-54 to produce 5 atoms of the isotope bohrium-262:[9]

209
83
Bi
+ 54
24
Cr
262
107
Bh
+ n

The IUPAC/IUPAP Transfermium Working Group (TWG) recognised the GSI collaboration as official discoverers in their 1992 report.[10]

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.[11]

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.[12] 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.[12][13] 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.[12]

Isotopes

List of bohrium isotopes
Isotope
Half-life
[14][15]
Decay
mode[14][15]
Discovery
year
Reaction
260Bh 35 ms α 2007 209Bi(52Cr,n)[16]
261Bh 11.8 ms α 1986 209Bi(54Cr,2n)[17]
262Bh 84 ms α 1981 209Bi(54Cr,n)[9]
262mBh 9.6 ms α 1981 209Bi(54Cr,n)[9]
263Bh 0.2? ms α ? unknown
264Bh 0.97 s α 1994 272Rg(—,2α)[18]
265Bh 0.9 s α 2004 243Am(26Mg,4n)[19]
266Bh 0.9 s α 2000 249Bk(22Ne,5n)[20]
267Bh 17 s α 2000 249Bk(22Ne,4n)[20]
268Bh 25? s α, SF? unknown
269Bh 25? s α ? unknown
270Bh 61 s α 2006 282Uut(—,3α)[21]
271Bh 1.2 s α 2003 287Uup(—,4α)[21]
272Bh 9.8 s α 2005 288Uup(—,4α)[21]
273Bh 90? min α, SF ? unknown
274Bh ~54 s α 2009 294Uus(—,5α)[6]
275Bh 40? min SF ? unknown

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. Eleven different isotopes of bohrium have been reported with atomic masses 260–262, 264–267, 270–272, 274, one of which, bohrium-262, has a known metastable state. All of these decay only through alpha decay, although some unknown bohrium isotopes are predicted to undergo spontaneous fission.[14]

Stability and half-lives

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. 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.[14]

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 four most neutron-rich ones with masses 270, 271, 272, and 274 appear in the decay chains of 282113, 287115, 288115, and 294117 respectively. These eleven isotopes have half-lives ranging from 8 milliseconds to 1 minute.[22]

Chemical properties

Extrapolated

Bohrium is 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 +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.

The heavier members of the group are known to form volatile heptoxides M2O7 (M = metal), 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.

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]

Experimental

In 1995, the first report on attempted isolation of the element was unsuccessful.[23]

In 2000, it was confirmed that although relativistic effects are important, the 107th element does behave like a typical group 7 element.[24]

In 2000, a team at the PSI conducted a chemistry reaction using 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.[25]

2 Bh + 3 O
2
+ 2 HCl → 2 BhO
3
Cl
+ H
2
Formula Name(s)
BhO3Cl bohrium oxychloride ; bohrium(VII) chloride trioxide

See also

References

  1. ^
  2. ^ a b c d e
  3. ^ a b c
  4. ^ a b
  5. ^ Chemical Data. Bohrium - Bh, Royal Chemical Society
  6. ^ a b (gives life-time of 1.3 min based on a single event; conversion to half-life is done by multiplying with ln(2).)
  7. ^ a b
  8. ^ Yu. Ts. Oganessian et al. On spontaneous fission of neutron-deficient isotopes of elements 103, 105 and 107 // Nuclear Physics A. — 1976. — Т. 273. — № 2. — С. 505-522.
  9. ^ a b c
  10. ^
  11. ^
  12. ^ a b c
  13. ^
  14. ^ a b c d
  15. ^ a b
  16. ^
  17. ^
  18. ^
  19. ^
  20. ^ a b
  21. ^ a b c
  22. ^
  23. ^
  24. ^
  25. ^ "Gas chemical investigation of bohrium (Bh, element 107)", Eichler et al., GSI Annual Report 2000. Retrieved on 2008-02-29

External links

  • Los Alamos National Laboratory – Bohrium
  • Cl3Properties of BhO
  • Bohrium at The Periodic Table of Videos (University of Nottingham)
  • WebElements.com – Bohrium
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