Seaborgium


Seaborgium

Seaborgium (pronEng|siːˈbɔrgiəm) is a chemical element in the periodic table that has the symbol Sg and atomic number 106, Image of Seaborgium . Seaborgium is a synthetic element whose most stable isotope 271Sg has a half-life of 1.9 minutes. Chemistry experiments with seaborgium have firmly placed it in group 6 as a heavier homologue to tungsten.

Official discovery

Element 106 was officially discovered in June 1974 by an American research team led by Albert Ghiorso at the Lawrence Radiation Laboratory at the University of California, Berkeley. They reported creating 263106, with a half-life of 1.0 s, by the hot fusion reaction:

:, ^{249}_{98}mathrm{Cf} + , ^{18}_{8}mathrm{O} , o , ^{263}_{106}mathrm{Sg} + 4, ^{1}_{0}mathrm{n}

A team led by Ken Gregorich at LBNL confirmed the synthesis in 1994.

The IUPAC/IUPAP Transfermium Working Group (TWG) officially recognised the LBNL team as discoverers in their 1992 report.http://www.iupac.org/publications/pac/1993/pdf/6508x1757.pdf (TWG report)]

Proposed names

(main article: Element naming controversy)

Historically, element 106 has been referred to as eka-tungsten.

The Berkeley team suggested the name "seaborgium" (Sg) to honor the American chemist Glenn T. Seaborg credited as a member of the American group in recognition of his participation in the discovery of several other actinides. The name selected by the team became controversial. An element naming controversy erupted and as a result IUPAC adopted "unnilhexium" (pronEng|ˌjuːnɪlˈhɛksiəm or IPA|/ˌʌnɪlˈhɛksiəm/, symbol "Unh") as a temporary, systematic element name. In 1994 a committee of IUPAC recommended that element 106 be named "rutherfordium" and adopted a rule that no element can be named after a living person. [http://www.iupac.org/publications/pac/1994/pdf/6612x2419.pdf (IUPAC 1994 recomm)] This ruling was fiercely objected to by the American Chemical Society. Critics pointed out that a precedent had been set in the naming of einsteinium during Albert Einstein's life and a survey indicated that chemists were not concerned with the fact that Seaborg was still alive. In 1997, as part of a compromise involving elements 104 to 108, the name "seaborgium" for element 106 was recognized internationally. [http://www.iupac.org/publications/pac/1997/pdf/6912x2471.pdf (IUPAC 1997 recomm)]

Electronic structure

Seaborgium is element 106 in the Periodic Table. The two forms of the projected electronic structure are:

Bohr model: 2, 8, 18, 32, 32, 12, 2

Quantum mechanical model: 1s22s22p63s23p64s23d104p65s24d105p66s24f145d106p67s25f146d4

Extrapolated chemical properties of eka-tungsten/dvi-molybdenum

Oxidation states

Element 106 is projected to be the third member of the 6d series of transition metals and the heaviest member of group VI in the Periodic Table, below chromium, molybdenum and tungsten.All the members of the group readily portray their group oxidation state of +VI and the state becomes more stable as the group is descended. Thus seaborgium is expected to form a stable +VI state.For this group, stable +V and +IV states are well represented for the heavier members and the +III state is known but reducing, unlike Cr(III).

Chemistry

Molybdenum and tungsten readily form stable trioxides MO3 Therefore, seaborgium should from SgO3. The oxides MO3 are soluble in alkali with the formation of oxyanions, so seaborgium should form a seaborgate ion, SgO42-. In addition, WO3 reacts with acid so again eka-tungsten reactivity will show a lack of amphotericity for SgO3. Molybdenum oxide, MoO3, also reacts with moisture to form a hydroxide MoO2(OH)2, so SgO2(OH)2 is also feasible.The heavier homologues readily form the volatile, reactive hexahalides MX6 (X=Cl,F). Only tungsten forms the unstable hexabromide, WBr6. Therefore, the compounds SgF6 and SgCl6 are predicted. An eka-tungsten character may show itself in the formation of a hexabromide, SgBr6. These halides are unstable to oxygen and moisture and readily form volatile oxyhalides, MOX4 and MO2X2. Therefore SgOX4 (X=F,Cl) and SgO2X2 (X=F,Cl) should be possible. In aqueous solution, a variety of anionic oxyfluoro-complexes are formed with fluoride ion, examples being MOF5- and MO3F33-. Similar seaborgium complexes are expected.

Experimental chemistry

Gas phase chemistry

Initial experiments aiming at probing the chemistry of seaborgium focused on the study of the gas thermochromatography of a volatile oxychloride.Seaborgium atoms were produced in the reaction 248Cm(22Ne,4n)266Sg, thermalised and reacted with an O2/HCl mixture. The resulting adsorption properties of the oxychloride was measured and compared with those of molybdenum and tungsten. The result indicated that seaborgium formed a volatile oxychloride in a manner akin to the group 6 elements:

:mathrm{Sg} + mathrm{O}_{2}/,mathrm{HCl} o ,mathrm{SgO}_{2}mathrm{Cl}_{2}

In 2001, a team continued the study of the gas phase chemsitry of seaborgium by reacting the element with O2 in a H2O environment. In a manner similar to the formation of the oxychloride, the results of the experiment indicated the formation of seaborgium oxide hydroxide, a reaction well-known with lighter group 6 homologues. [ [http://www-w2k.gsi.de/kernchemie/images/pdf_Artikel/Radiochim_Acta_89_737_2001.pdf "Physico-chemical characterization of seaborgium as oxide hydroxide"] , Huebener et al., "Radiochim. Acta", 89, 737–741 (2001).Retrieved on 2008-02-29]

:2,mathrm{Sg} + 3,mathrm{O}_{2} o 2,mathrm{SgO}_{3}:mathrm{SgO}_{3} + mathrm{H}_{2}mathrm{O} o mathrm{SgO}_{2}(mathrm{OH})_{2}

Aqueous phase chemistry

In its aqueous chemistry, seaborgium has been shown to resemble its lighter homologues molybdenum and tungsten in group 6, forming a stable +6 oxidation state. Seaborgium was eluted from cation exchange resin using a HNO3/HF solution, most likely as neutral SgO2F2 or the anionic complex ion [SgO2F3] -. In contrast, in 0.1 M HNO3, seaborgium does not elute, unlike Mo and W, indicating that the hydrolysis of [Sg(H2O)6] 6+ only proceeds as far as the cationic complex [Sg(OH)5(H2O] +.

ummary of investigated compounds and complex ions

Isotopes

There are 11 known isotopes of seaborgium (exclusing meta-stable and K-spin isomers). The longest-lived is 271Sg which decays through alpha decay and spontaneous fission. It has a half-life of 1.9 minutes. The shortest-lived isotope is 258Sg which also decays through alpha decay and spontaneous fission. It has a half-life of 2.9 ms.

Isomerism in seaborgium nuclides

266Sg

Initial work identified an 8.63 MeV alpha-decaying activity with a half-life of ~21s and assigned to the ground state of 266Sg. Later work identified a nuclide decaying by 8.52 and 8.77 MeV alpha emission with a half-life of ~21s, which is unusual for an even-even nuclide. Recent work on the synthesis of 270Hs identified 266Sg decaying by SF with a short 360 ms half-life. The recent work on 277112 and 269Hs has provided new information on the decay of 265Sg and 261Rf. This work suggested that the initial 8.77 MeV activity should be reassigned to 265Sg. Therefore the current information suggests that the SF activity is the ground state and the 8.52 MeV activity is a high spin K-isomer. Further work is required to confirm these assignments. A recent re-evaluation of the data has suggested that the 8.52 MeV activity should be associated with 265Sg and that 266Sg only undergoes fission.

265Sg

The recent direct synthesis of 265Sg resulted in four alpha-lines at 8.94,8.84,8.76 and 8.69 MeV with a half-life of 7.4 seconds. The observation of the decay of 265Sg from the decay of 277112 and 269Hs indicated that the 8.69 MeV line may be associated with an isomeric level with an associated half-life of ~ 20 s. It is plausible that this level is causing confusion between assignments of 266Sg and 265Sg since both can decay to fissioning rutherfordium isotopes.

A recent re-evaluation of the data has indicated that there are indeed two isomers, one with a principal decay energy of 8.85 MeV with a half-life of 8.9 s, and a second isomer which decays with energy 8.70 MeV with a half-life of 16.2 s.

263Sg

The discovery synthesis of 263Sg resulted in an alpha-line at 9.06 MeV. Observation of this nuclide by decay of 271gDs, 271mDs and 267Hs has confirmed an isomer decaying by 9.25 MeV alpha emission. The 9.06 MeV decay was also confirmed. The 9.06 MeV activity has been assigned to the ground state isomer with an associated half-life of 0.3 s. The 9.25 MeV activity has been assigned to an isomeric level decaying with a half-life of 0.9 s.

Recent work on the synthesis of 271g,mDs was resulted in some confusing data regarding the decay of 267Hs. In one such decay, 267Hs decayed to 263Sg which decayed by alpha emission with a half-life of ~ 6 s. This activity has not yet been positively assigned to an isomer and further research is required.

pectroscopic decay schemes for seaborgium isotopes

261Sg

Retracted isotopes

269Sg

In the claimed synthesis of 293118 in 1999 the isotope 269Sg was identified as a daughter product. It decayed by 8.74 MeV alpha emission with a half-life of 22 s. The claim was retracted in 2001 and thus this seaborgium isotope is currently unknown or unconfirmed. [see ununoctium]

Chemical yields of isotopes

Cold fusion

The table below provides cross-sections and excitation energies for cold fusion reactions producing seaborgium 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 seaborgium 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/Sg/index.html WebElements.com - Seaborgium]


Wikimedia Foundation. 2010.

Look at other dictionaries:

  • Seaborgium — Dubnium ← Seaborgium → Bohrium W …   Wikipédia en Français

  • seaborgium — [sē bôr′gē əm] n. 〚ModL, after SEABORG Glenn T(heodore) + IUM〛 a radioactive chemical element with a very short half life: a transactinide produced by bombarding californium or lead with high energy nuclear particles: symbol, Sg; at. no., 106:… …   Universalium

  • seaborgium — ● seaborgium nom masculin (de G. T. Seaborg, nom propre) Élément chimique artificiel (Sg) de numéro atomique 106, de masse atomique 263,1186 …   Encyclopédie Universelle

  • seaborgium — Name proposed for the 106th element (unnilhexium) by the American Chemical Society in honor of Gleen T. Seaborg, an American nuclear physicist and Nobel prize winner …   Elements of periodic system

  • seaborgium — [sē bôr′gē əm] n. [ModL, after SEABORG Glenn T(heodore) + IUM] a radioactive chemical element with a very short half life: a transactinide produced by bombarding californium or lead with high energy nuclear particles: symbol, Sg; at. no., 106:… …   English World dictionary

  • Seaborgium — Eigenschaften …   Deutsch Wikipedia

  • Seaborgium — siborgis statusas T sritis fizika atitikmenys: angl. seaborgium vok. Seaborgium, n rus. сиборгий, m pranc. seaborgium, m …   Fizikos terminų žodynas

  • seaborgium — siborgis statusas T sritis fizika atitikmenys: angl. seaborgium vok. Seaborgium, n rus. сиборгий, m pranc. seaborgium, m …   Fizikos terminų žodynas

  • seaborgium — siborgis statusas T sritis chemija apibrėžtis Cheminis elementas. simbolis( iai) Sg atitikmenys: lot. seaborgium angl. seaborgium rus. сиборгий …   Chemijos terminų aiškinamasis žodynas

  • seaborgium — noun Etymology: New Latin, from Glenn T. Seaborg Date: 1994 a short lived radioactive element that is produced artificially see element table …   New Collegiate Dictionary


Share the article and excerpts

Direct link
Do a right-click on the link above
and select “Copy Link”

We are using cookies for the best presentation of our site. Continuing to use this site, you agree with this.