ncert books class 12 chemistry chapter 4 · Section 1

The d- block of the periodic table contains the elements of the groups - in which the d orbitals are progressively filled in each of the four long periods. The f -block consists of elements in which f and f orbitals are progressively filled. They are placed in a separate panel at the bottom of the periodic table. The names transition metals and inner transition metals are often used to refer to the elements of d -and f -blocks respectively. There are mainly four series of the transition metals, d series (Sc to Zn), d series (Y to Cd), d series (La and Hf to Hg) and d series which has Ac and elements from Rf to Cn. The two series of the inner transition metals; f (Ce to Lu) and f (Th to Lr) are known as lanthanoids and actinoids respectively. Originally the name transition metals was derived from the fact that their chemical properties were transitional between those of s and p -block elements. Now according to IUPAC, transition metals are defined as metals which have incomplete d subshell either in neutral atom or in their ions. Zinc, cadmium and mercury of group have full d configuration in their ground state as well as in their common oxidation states and hence, are not regarded as transition metals. However, being the end members of the d , d and d transition series, respectively, their chemistry is studied along with the chemistry of the transition metals. The presence of partly filled d or f orbitals in their atoms makes transition elements different from that of