Bismuth relativistic effects

While the contraction resulting from the poor shielding of 4/ electrons ceases at hafnium, the relativistic effect continues across the sixth row of the periodic table. It is largely responsible for the stabilization of the 6. orbital and the inert s pair effect shown by the elements Hg-Bi. It also stabilizes one40 of the 6p orbitals of bismuth allowing the unusual i-l oxidation state in addition to +3 and + 5.4 ... 

Precise measurements on g factors of electrons bound in atomic Hydrogen and the Helium ion 4He+ were carried out by Robinson and coworkers. The accuracies of 3 x 10-8 for the Hydrogen atom [5] and of 6 x 10-7 for the Helium ion [6] were sensitive to relativistic effects. Other measurements of the magnetic moment of the electron in Hydrogen-like ions were performed at GSI by Seelig et al. for Lead (207Pb81+) [7] and by Winter et al. for Bismuth (209Bi82+) [8] with precisions of about 10-3 via lifetime measurements of hyperfine transitions. These measurements were also only sensitive to the relativistic contributions. 

Thus, the main relativistic effects are (1) the radical contraction and energetic stabilization of the s and p orbitals which in turn induce the radial expansion and energetic destabilization of the outer d and f orbitals, and (2) the well-known spin-orbit splitting. These effects will be pronounced upon going from As to Sb to Bi. Associated with effect (1), it is interesting to note that the Bi atom has a tendency to form compounds in which Bi is trivalent with the 6s 6p valence configuration. For this tendency of the 6s electron pair to remain formally unoxidized in bismuth compounds (i.e. core-like nature of the 6s electrons), the term inert pair effect or nonhybridization effect has been often used for a reasonable explanation. In this context, the relatively inert 4s pair of the As atom (compared with the 5s pair of Sb) may be ascribed to the stabilization due to the d-block contraction , rather than effect (1) . On the other hand, effect (2) plays an important role in the electronic and spectroscopic properties of atoms and molecules especially in the open-shell states. It not only splits the electronic states but also mixes the states which would not mix in the absence of spin-orbit interaction. As an example, it was calculated that even the ground state ( 2 " ) of Bij is 25% contaminated by Hg. In the Pauli Hamiltonian approximation there is one more relativistic effect called the Dawin term. This will tend to counteract partially the mass-velocity effect. 

In order to explain this important new effect on the periodic system, we need to see how relativistic effects change the properties of valence electrons in the region of element 114. In Fig. 24.S we see the radii of the pi/2 and P3/2 valence electrons of antimony, bismuth, and element IIS (eka-bismuth). We pick element 115 for this discussion for the moment because the point is better made with it than with 114. In antimony the splitting between the p electrons of total angular momentum 1 /2 and the p electrons with total angular momentum 3/2 is so small as to be of no importance. Also we just speak of a Sp configuration for antimony, and the designation ofpi/2 and P3/2 is actually somewhat artificial from the point of view of its chemistry. This same story is almost, but not quite, true for bismuth. It is. 

Although all of the superheavy elements will show relativistic effects in their chemistry, the clearest case may be element 115 (eka-bismuth), which we have used for illustration above. Keller, Nestor, and Fricke [25] have made some detailed predictions of the chemical properties of element 115 based on extrapolations of the properties of elements of group V and relativistic calculations of electronic structure. Their results indicate that the chemical... 

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