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Sun Mar 11, 2018, 08:17 AM

Copernecium forms a mercury like amalgam with gold.

I'm going through old papers I collected 10 years ago but never read, and I came across this oldie but goodie from 2007, which somehow found its way into a directory about the environmental and climate impact of large dams, along with an obituary of John Wheeler:

Chemical characterization of element 112 (R. Eichler, N. V. Aksenov, A. V. Belozerov, G. A. Bozhikov, V. I. Chepigin, S. N. Dmitriev, R. Dressler, H. W. Gäggeler, V. A. Gorshkov, F. Haenssler, M. G. Itkis, A. Laube, V. Ya. Lebedev, O. N. Malyshev, Yu. Ts. Oganessian, O. V. Petrushkin, D. Piguet, P. Rasmussen, S. V. Shishkin, A. V. Shutov, A. I. Svirikhin, E. E. Tereshatov, G. K. Vostokin, M. Wegrzecki & A. V. Yeremin, Nature volume 447, pages 72–75 (03 May 2007))

One of the most dubious mining practices in the world is the extraction of gold from ores using liquid mercury, because mercury readily dissolves gold, which historically was the most problematic element to dissolve, at least until the discovery of a mixture of acids, hydrochloric and nitric acid, known as "aqua regia" because it dissolves "the king of metals." Aqua regia however is somewhat less effective when recovering gold from ores than mercury, and therefore mercury is still utilized for this purpose, particularly in wild cat mining of the type utilized to recover not only gold but many diffuse elements such as tantalum and the lanthanides, leading to distributed pollution that is difficult to address.

To recover gold from solution in liquid mercury, the mercury is distilled off.



Element 112, now known as the element Copernicium, is a cogener of the toxic metals mercury and cadmium, the toxicity of which is largely an effect related to their displacing another cogener, zinc, in metalloenzymes, thus inactivating them.

The ten year old paper linked above refers to its chemistry, which has been the subject of some interest owing to relativistic corrections to its electronic structure, a topic to which the wonderful host of this group, directed my attention recently. It has not been clear whether or not Copernicium would be an inert gas rather like radon or a liquid. From the text:

The heaviest elements to have been chemically characterized are seaborgium1 (element 106), bohrium2 (element 107) and hassium3 (element 108). All three behave according to their respective positions in groups 6, 7 and 8 of the periodic table, which arranges elements according to their outermost electrons and hence their chemical properties. However, the chemical characterization results are not trivial: relativistic effects on the electronic structure of the heaviest elements can strongly influence chemical properties4–6. The next heavy element targeted for chemical characterization is element 112; its closed-shell electronic structure with a filled outer s orbital suggests that it may be particularly susceptible to strong deviations from the chemical property trends expected within group 12. Indeed, first experiments concluded that element 112 does not behave like its lighter homologue mercury7–9. However, the production and identification methods 10,11 used cast doubt on the validity of this result...

The systematic order of the periodic table places element 112 in group 12, which also includes zinc, cadmium and mercury. It should thus have the closed-shell electronic ground state configuration Rn: 5f 146d107s 2, which implies noble metal characteristics16. However, relativistic calculations of atomic properties of superheavy elements suggest4–6 contraction of the spherical s- and p1/2-electron orbitals. The effect may increase the chemical stability of the elemental atomic state of element 112 beyond that of a noble metal and endow it with inertness more similar to that of the noble gas radon17, although recent relativistic calculations on element 112 predicted18 that it should form a semiconductor-like solid with clear chemical bonds. It was suggested19 that the questions of the bonding characteristics of element 112 and whether it more strongly resembles a noble metal or a noble gas might be addressed experimentally, by determining its gas adsorption properties on a noble metal surface such as gold. In fact, relativistic calculations indicate that the spin-orbit splitting of the 6d orbitals results in element 112 having a ground-state configuration with a 6d5/2 outermost valence orbital, which would make it behave like a noble transition metal20,21. Moreover, relativistic density functional calculations of its interaction with noble metals predict metallic interactions similar to those of the lighter homologue mercury22–24...

... By directly comparing the adsorption characteristics of 283(Cn) to that of mercury and the noble gas radon, we find that element 112 is very volatile and, unlike radon, reveals a metallic interaction with the gold surface...

Some interesting details about this elegant experiment requiring significant teamwork:

Thermochromatography allows very efficient probing of the interaction potential of volatile gas-phase species with stationary surfaces over a broad range of interaction enthalpies.We used the in situ volatilization and on-line detection method28 for thermochromatography measurements at temperatures between135 uC and 2186 uC, with the original system modified and significantly improved11,29 to enable gas adsorption investigations of element 112 on gold surfaces. Figure 1 depicts schematically the experimental set-up. A target of 242PuO2 (1.4mg cm22 242Pu) with an admixture of nat.Nd2O3 (15 mg cm22 of Nd of natural isotopic composition) was deposited on a thin (0.7mg cm22) Ti backing foil and irradiated for about three weeks at the U-400 cyclotron at FLNR with 3.131018 48Ca particles at a primary energy of 27063MeV. The beam energy in themiddle of the target was 23663MeV, corresponding to the maximum of the production cross-section of 287Fl in the 242Pu(48Ca, 3n) reaction channel12. The irradiation generated not only 287Fl, but also the partially alphadecaying nuclide 185Hg with a half-life of 49 s. This nuclide is produced in the reaction 142Nd(48Ca, 5n) and serves in our experiment as a monitor for the production and separation process. Various isotopes of radon (for example, 219Rn, with a half-life of 4 s) were also produced in multi-nucleon transfer reactions between 48Ca and 242Pu. Thus, radon and mercury were studied simultaneously with element 112 throughout the experiment.

Cool, I think.

The conclusion:

The statistical Monte Carlo approach to modelling the gas chromatography results17,30 uses adsorption enthalpy values to mimic the observed deposition patterns, which provides upper and lower limits for the adsorption enthalpy of element 112 on gold2DHads Au(E112) of 98 kJ mol21 and 45 kJ mol21 (68% confidence interval), respectively; it also yields a most probable value of 2DHads Au(E112) 552 kJ mol21, which has a large associated uncertainty due to the small number of observed events (see also Supplementary Information section 2). Still, the range of likely adsorption enthalpies inferred from this study indicates an interaction between element 112 and gold that is significantly stronger than the purely dispersive van der Waals interactions of noble-gas like elements27. We therefore conclude that the stronger adsorption interaction of element 112 with gold involves formation of a metal bond, which is behaviour typical of group 12 elements.

The added bold is mine.

(Cn substituted for 112 and Fl for 114 in the original text where needed to distinguish the mass number from the atomic number, owing to the inability to utilize superscripts here.)

The host here recently directed me to a wonderful paper on the effects of relativity on the chemistry of heavy elements, which by the way, is evoked to account for the fact that mercury is a liquid rather than a solid.

It is here: Relativistic Effects in Chemistry: More Common Than You Thought (Pyykkö, Annual Review of Physical Chemistry, Vol. 63:45-64 (Volume publication date May 2012)

Have a nice Daylight Savings Time Sunday afternoon.

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