The use of Rich and Suter diagrams to explain the electron configurations of transition elements

Abstract

Recebido em 25/9/12; aceito em 2/2/13; publicado na web em 24/5/13Rich and Suter diagrams are a very useful tool to explain the electron configurations of all transition elements, and in particular, the s 1 and s 0 configurations of the elements Cr, Cu, Nb, Mo, Ru, Rh, Pd, Ag, and Pt. The application of these diagrams to the inner transition elements also explains the electron configurations of lanthanoids and actinoids, except for Ce, Pa, U, Np, and Cm, whose electron configurations are indeed very special because they are a mixture of several configurations.Keywords: periodic table; electronic configuration; Rich and Suter diagrams.The electronic configuration of chemical elements is a very important and initial topic in all introductory chemistry courses. To obtain them, the Aufbau principle is used in connection with the orbitals energies. However, the explanation of the s 1 ground-state electron configurations of Cr and Cu is generally based on the special stability attributed to a half-filled and filled subshell, respectively. 1-3Otherwise, these configurations can be explained by the very elegant Rich and Suter diagrams. 4 These and some other authors clearly state that there is no extra stability for a filled or half-filled subshell compared with a subshell containing one electron less. [4][5][6][7] The s 1 and s 0 electron configurations of neutral isolated atoms of some transition elements can be explained by considering that each subshell energy level is split into two levels, a and b, related to the spin of the electrons, as can be seen in Figure 1. The Coulomb energy on account of the pairing of two electrons in the same orbital is assigned to the b level, because of which this level appears to be at a higher energy than the a level. In Figure 1a, the number 6 at the crossing point between the 3da and 4sa lines has the meaning 3da 5 and 4sa 1 , and the same meaning applies to Figure 1c.This type of diagram is very easily grasped by students and makes the explanation of the "anomalous" s 1 and s 0 electron configurations of transition elements much more reasonable. As can be seen in Figure 1a, the 4s 2 3d 3 vanadium electron configuration comes from the fact that both levels, 4sa and 4sb, have a lower energy than 3da. As we move to the right on the periodic table, the atomic number increases and all the levels go down. Because the 3d levels are closer to the core, they decrease faster than the 4s level, and the 3da level crosses the 4sb level when passing from V to Cr. It causes that for Cr, the 3da level must be completely filled with five electrons before we can put any electrons in the 4sb level. Because Cr only has six electrons in the valence shell, there is no electron to occupy the 4sb level, which results in the 4s 1 3d 5 electron configuration of Cr. The same situation occurs upon going from Ni to Cu. For Ni, the 4sb level is below 3db, whereas for Cu these levels cross and 3db becomes lower than 4sb. This means that the levels must be filled in the sequence: 3da 5 4sa 1 3db 5 , and because ...

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