Ground state electronic configurations

   d-Block metals versus transition elements The three rows of d-block metals are shown in the schematic periodic table at the beginning of the chapter. The term ‘transition elements (metals)’ is also widely used, but ‘d-block metal’ and ‘transition element’ are not interchangeable. A transition element is one for which an atom has an incompleted-subshell, or which gives rise to a cation with an incomplete d-subshell , and thus elements in group 12 (which are within the d-block) are not transition elements.  

  Throughout our discussions, we shall use the terms d-block and f-block metals, so being consistent with the useof the terms s-block and p-block elements in earlier chapters. Three further points should be noted:

• each group of d-block metals consists of three members and is called a triad; . metals of the second and third rows are sometimes called the heavier d-block metals;
•  Ru, Os, Rh, Ir, Pd and Pt are collectively known as the platinum-group metals.

Electronic configurations

   To a first approximation, the observed ground state electronic configurations of the first, second and third row d-block metal atoms correspond to the progressive filling of the 3d, 4d and 5d atomic orbitals respectively. However, there are minor deviations from this pattern, e.g. in the first row, the ground state of chromium is [Ar]4s¹3d⁵ rather than [Ar]4s²3d⁴. The reasons for these deviations are beyond the scope of this book: we should need to know both the energy difference between the 3d and 4s atomic orbitals when the nuclear charge is 24 (the atomic number of Cr) and the interelectronic interaction energies for each of the [Ar]4s¹3d⁵ and [Ar]4s²3d⁴ configurations. Fortunately, M^2+‏ and M^3+‏ ions of the first row d-block metals all have electronic configurations of the general form [Ar]3dⁿ, and so the comparative chemistry of these metals is largely concerned with the consequences of the successive filling of the 3d orbitals. For metals of the second and third rows, the picture is more complicated, and a systematic treatment of their chemistry cannot be given. The emphasis in this and the next chapter is therefore on the first row metals, but we shall include some material that illustrates ways in which the heavier metals differ from their lighter congeners.   An important point that must not be forgotten is that dblock metal atoms are, of course, many-electron species, and when we discuss, for example, radial distribution functions of the nd atomic orbitals, we refer to hydrogen like atoms and, therefore, the discussion is extremelya pproximate.