S. N. Timokhin

Chemical properties of element 106 (seaborgium)

The synthesis, via nuclear fusion reactions, of elements heavier than the actinides, allows one to probe the limits of the periodic table as a means of classifying the elements. In particular, deviations in the periodicity of chemical properties for the heaviest elements are predicted as a consequence of increasingly strong relativistic effects on the electronic shell structure. The transactinide elements have now been extended up to element 112 (ref. 8), but the chemical properties have been investigated only for the first two of the transactinide elements, 104 and 105 (refs 9,10,11,12,13,14,15,16,17,18,19). Those studies showed that relativistic effect render these two elements chemically different from their lighter homologues in the same columns of the periodic table (Fig. 1). Here we report the chemical separation of element 106 (seaborgium, Sg) and investigations of its chemical behaviour in the gas phase and in aqueous solution. The methods that we use are able to probe the reactivity of individual atoms, and based on the detection of just seven atoms of seaborgium we find that it exhibits properties characteristic of the group 6 homologues molybdenum and tungsten. Thus seaborgium appears to restore the trends of the periodic table disrupted by relativistic effects in elements 104 and 105.

First Measurement of a Thermochemical Property of a Seaborgium Compound.

With only a few atoms of seaborgium (Sg, element 106), in the form of volatile SgO(2)Cl(2), it was possible to determine the sublimation enthalpy of this compound using gas chromatography. Furthermore, it was demonstrated that in Group 6 Sg is chemically more similar to W than to Mo.

Evidence for relativistic effects in the chemistry of element 104

Abstract On the basis of thermodynamic extrapolations, the first transactinide element 104 (Rf=rutherfordium 1 ) is expected to form volatile tetrachlorides of lower volatility than those of the homologous element Hf. In contrast, relativistic calculations predict a higher volatility of RfCl 4 compared to HfCl 4 . The nuclides 261 Rf and 165 Hf, with identical half-lives of 78 s, were simultaneously produced at the U-400 cyclotron of the Flerov Laboratory of Nuclear Reactions (FLNR), Dubna, Russia, by bombarding a mixed 248 Cm/ 152 Gd target with 18 O ions. With the on-line gas chemistry apparatus (OLGA), the retention behavior of volatile Rf- and Hf-chloride in a quartz chromatography column was investigated. The results showed that Rf forms chlorides of higher volatility than those of Hf, in agreement with relativistic calculations. In addition, the behavior of element 104 was investigated in chlorinating, oxygen containing carrier gas, in order to answer the question whether a volatile compound of the form RfOCl 2 exists. The results of our experiments give strong evidence for a transport reaction mechanism where RfOCl 2 exists only in the condensed phase and not in the gas phase.

Erste experimentelle Bestimmung einer thermochemischen Größe einer Seaborgiumverbindung

Nur wenige Atome von Seaborgium (Sg, Element 106), die zu fluchtigem SgO2Cl2 umgesetzt wurden, reichten aus, um die Sublimationsenthalpie dieser Verbindung gaschromatographisch zu bestimmen. Daruber hinaus wurde gezeigt, das Sg in der Gruppe 6 eher mit W verwandt ist als mit Mo.

Thermochromatography of heavy actinides adsorption of No-259 on Ti, V, Nb, Ta and Mo

Abstract The adsorption of elemental No on Ti, V, Nb, Ta and Mo was studied in comparison to Cf, Es and Fm by thermochromatography. The adsorption enthalpy values of No show the predicted metallic divalency of this element. This is confirmed by calculations with two semiempirical models developed by Eichler [1] and Miedema [2] . Using the experimentally proved correlation between adsorption and sublimation enthalpies, we calculated the No sublimation enthalpy to be 134±15 kJ mol −1 .