Definition and Electronic Configurations of Atoms The elements lying between s and p-block elements of the periodic table are collectively known as transition or transitional elements (T.E.’s):
These elements either in their atomic state or in any of their common oxidation state have partly filled (n-1) d-orbitals of (n-1)th main shell.
In these elements the differentiating electron enters (n-1)d orbitals of (n-1)th main shell and as such these are called d-block elements.
The valence shell configurations of these elements can be represented by (n-1)d1-10.ns0 , 1 , 2. The configurations clearly show that strictly, according to the definition of d-block elements, Cu, Ag and Au should be excluded from d-block elements, since these elements, both in their atomic state [with configuration (n-1)d10ns1] and in their +1 oxidation state [with configuration (n-1)d10], do not have partly filled (n – 1)d-orbitals.
Similarly Zn, Cd and Hg which both in their atomic state [(n-1)d10ns2 ] and in +2 oxidation [(n-1)d10] do not contain partly filled (n-1)d orbitals, should also be excluded from d-block elements.
Similar is the case with Pd atom with configuration 4d105s0. Yet, in order to maintain a rational classification of elements, these elements (viz Cu, Ag, Au, Zn, Cd, Hg and Pd) are also generally studied with d-block elements.
All the d-block elements are classified into four series viz 3d, 4d, 5d and 6d series corresponding to the filling of 3d, 4d, 5d and 6d orbitals of (n-1)th main shell. Each of 3d, 4d and 5d series has ten elements while 6d series has at present only one element viz Ac80 whose valence shell configuration is 6d1 7s2.
Next Page »
Irregularities in Configurations