INTRODUCTION
The d-block of the periodic table consists of the elements of groups 3-12 in which the d orbitals are progressively filled in each of the four long periods. The f-block consists of elements in which 4 f and 5 f orbitals are progressively filled. These are placed in a separate panel at the bottom of the periodic table. The elements of d-and f-blocks are often called as transition metals and inner transition metals respectively.
There are mainly four series of transition metals, 3d series (Sc to Zn), 4d series (Y to Cd), 5d series (La and Hf to Hg) and 6d series which has Ac and elements from Rf to Cn. The two series of the inner transition metals; 4f (Ce to Lu) and 5f (Th to Lr) are known as lanthanoids and actinoids respectively. The name transition metals were Originally derived from the fact that their chemical properties were transitional between those of s and p-block elements.
As per IUPAC, transition metals are defined as metals which have incomplete d subshells either in the neutral atom or in their ions. Zinc, cadmium and mercury of group 12 have full d 10 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 3d, 4d and 5d 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 the d- and f – Block Elements. The d- and f-Block Elements Iron, copper, silver and gold are among the transition elements that have played important roles in the development of human civilisation. The inner transition elements such as Th, Pa and U are proving excellent sources of nuclear energy in modern times. Therefore, transition elements and their compounds are studied separately. However, the usual theory of valence as applicable to the non-transition elements can be applied successfully to the transition elements also. Various precious metals such as silver, gold and platinum and industrially important metals like iron, copper and titanium belong to the transition metals series. In this Unit, we shall first deal with the electronic configuration, occurrence and general characteristics of transition elements with special emphasis on the trends in the properties of the first row (3d) transition metals along with the preparation and properties of some important compounds. Followed by certain general aspects such as electronic configurations, oxidation states and chemical reactivity of the inner transition metals.
CONTENT
Position in the Periodic Table, Electronic Configurations of the d-Block Elements, General Properties of the Transition Elements, (d-Block) Some Important Compounds of Transition Elements, The Lanthanoids, The Actinoids, Some Applications of d- and f-Block Elements
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