What is a Transition Element

The transition elements comprise groups 3 to 12 and are found in the central region of the standard periodic table, an example of which is reproduced on the endpaper. This group is further subdivided into those of the first row (the elements scandium to zinc), the second row (the elements yttrium to cadmium) and the third row (the elements lanthanum to mercury). The term transition arises from the elements supposed transitional positions between the metallic elements of groups 1 and 2 and the predominantly non-metallic elements of groups 13 to 18. Nevertheless, the transition elements are also, and interchangeably, known as the transition metals in view of their typical metallic properties. 

The outer configurations of the transition metals in Table 1-1 imply, and detailed spectroscopic investigations confirm, that the 3d orbitals lie at higher energies than the 45 orbitals. On the other hand, the configurations of the ions listed, in 

Transition MetalChemistry.M. Gerloch, E. C. Constable Copyright 1994 VCH Verlagsgesellschaft mbH, Weinheim ISBN 3-527-29218-7 

The explanation of these facts is not difficult but is subtle. We recall that the energies of all hydrogen orbitals belonging to the same principal quantum shell (n) are equal the d, 3p and 35 hydrogen orbitals are degenerate. These orbital subsets 

Chromium [Ar]3dHs° [Ar]3dHs Copper [Ar]34Ms° [Ar]34H5  

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