Transition Metals Definition - The d-block elements are called transition metal. The d-block consists of the elements that are lying in between the s and p blocks. The position of this block is between groups 2 and 13 in the periodic table. It starts from the fourth period onwards. In these elements, the outermost shell contains one or two electrons in their s-orbital but the last electron enters the last but one d subshell (n-1) d. The properties of the elements of this block generally lie between the elements of s block and p block.
Transition Elements List
The transition elements list contain the metals that have incompletely filled d-subshells in their ground state or any one of their oxidation states. Metals included in the transition elements list are:
First Transition Series
The first transition series consists of elements from scandium, Sc (Z = 21) to zinc, Zn (Z = 30) i.e scandium, titanium, vanadium, chromium, manganese, iron, cobalt, nickel, copper, and zinc. The first transition element is scandium, in scandium, the 3d orbital starts filling up and its electronic configuration is [Ar] 4s2 3d1. As we move from scandium onwards, 3d orbitals get filled up more and more till the last element, zinc, in which the 3d orbitals are completely filled [Ar] 4s2 3d10.
Exceptional Electronic Configuration of Chromium (Cr) and Copper (Cu) in Transition Series
The configuration of chromium and copper are anomalous. We know that half-filled and filled electronic configurations have extra stability associated with them. Moreover, the energy difference between 3d and 4s orbitals is not large enough to prevent the electron from entering the 3d orbitals. Thus, to acquire increased stability, one of the 4s electrons goes to nearby 3d orbitals so that the 3d orbital becomes half-filled in the case of chromium and filled in the case of copper respectively. Therefore, the electronic configuration of chromium is [Ar] 3d5 4s1 rather than [Ar] 3d4 4s2 while that of copper is [Ar] 3d10 4s1 instead of [Ar] 3d9 4s2.
Second Transition Series
The 2nd transition series consists of elements from yttrium, Y (Z = 39) to cadmium, Cd (Z = 48), i.e., yttrium, zirconium, niobium, molybdenum, technetium, ruthenium, rhodium, palladium, silver and cadmium. This series involves the filling of 4d-orbitals.
Third Transition Series
This series consists of elements of lanthanum and from hafnium to mercury i.e., lanthanum, hafnium, tantalum, tungsten, rhenium, osmium, iridium, platinum, gold, and mercury. In between Lanthanum and Hafnium there are fourteen elements called lanthanides which involve the filling of 4f-orbitals and do not belong to this series. The elements of the d-block third series involve the gradual filling of five d-orbitals. It may be noted that, in the second and third transition series, there are many anomalous configurations in comparison to those of the first transition series. These are accredited to the factors like nuclear electron and electron-electron forces.
Fourth Transition Series
It involves the filling of a 6d subshell starting from actinium (Z=89); which has the configuration 6d1 7s2. This fourth transition series in periodic table is incomplete as given in the table below:
General Characteristics of Transition Metals Elements are:
have high tensile strength.
High thermal conductivity.
Except for mercury which is liquid at room temperature, other transition elements have typical metallic structures.
Transition elements possess a high melting point and high boiling points.
The value of heats of vaporisation is higher than the non-transition elements.
The transition elements have very high densities as compared to the metal of group 1 and 2nd (s block).
The first ionisation energies of d block elements are higher than those of s block elements but are lesser than those of p block elements.
Did You Know?
The fundamental difference in the electronic configuration of transition elements and representative elements is that in the representative elements the valence electrons are present only in the outermost shell. On the other hand, in the transition elements, the valence electrons are present in the outermost shell (ns) as well as the d orbital of the penultimate shell.
The ionization energy of chromium and copper have an exceptionally higher energy than those of their neighbours.