Notes On d-Block: Complexes, Interstitial Compounds, Alloy Formation And Catalytic Properties - CBSE Class 12 Chemistry
The transition elements have a tendency to form coordination compounds or complex compounds. Complex compounds are those in which a central atom or ion is surrounded by a number of anions or neutral molecules possessing a lone pair of electrons. These surrounding anions or molecules are called ligands. EX: Pentamine Cobalt (iii) Chloride, Potassiumferrocyanide (ll), and Nickel Tetra Carbonyl (0). The tendency of the transition metal ions to form complexes is due to: Their relatively small size and resultant high positive charge density Presence of vacant n minus one d-orbitals Their ability to show multiple oxidation states Catalytic properties: Transition metals and their compounds catalyse various reactions of industrial importance. Ex: V2O5 is used in the manufacture of sulphuric acid by the contact process Finely divided iron is used in Haber's process for the manufacture of ammonia. Nickel is used in the hydrogenation of oils. Formation of interstitial compounds: Interstitial compounds are compounds of indefinite structure and composition. They are formed by the incorporation of small atoms like hydrogen, boron, carbon or nitrogen in the spaces between the metal atoms, that is, the interstices of the lattice. These substances are also known as non-stoichiometric substances. EX: Fe0.94O, TiC, Mn4N, Fe3H, VH0.56 and TiH1.7. The important physical and chemical Characteristics of these compounds are: They are extremely hard; some borides approach diamond in hardness. They have higher melting points than those of pure metals. They are chemically inert. They possess good electrical conductivity. Alloy formation: An alloy may be defined as a homogeneous mixture of a metal with other metals or metalloids, and sometimes even a non-metal. The atomic radii of the transition elements in any series are not too different from each other. As a result, they can very easily replace each other in the lattice, and thus, readily form alloys. Alloys are classified according to their components into two distinct types, namely, ferrous and non-ferrous. Ferrous alloys: Ferrous alloys contain iron, carbon, and one or two of the other elements like chromium, vanadium, tungsten and molybdenum. Non-ferrous alloys: These alloys do not contain iron as one of the components. The number of non-ferrous alloys used in technology is very large. EX: aluminium-bronze, duralumin magnalumin and electron. Brass an alloy of copper and zinc, and bronze, an alloy of copper and tin, are also important non-ferrous alloys.

#### Summary

The transition elements have a tendency to form coordination compounds or complex compounds. Complex compounds are those in which a central atom or ion is surrounded by a number of anions or neutral molecules possessing a lone pair of electrons. These surrounding anions or molecules are called ligands. EX: Pentamine Cobalt (iii) Chloride, Potassiumferrocyanide (ll), and Nickel Tetra Carbonyl (0). The tendency of the transition metal ions to form complexes is due to: Their relatively small size and resultant high positive charge density Presence of vacant n minus one d-orbitals Their ability to show multiple oxidation states Catalytic properties: Transition metals and their compounds catalyse various reactions of industrial importance. Ex: V2O5 is used in the manufacture of sulphuric acid by the contact process Finely divided iron is used in Haber's process for the manufacture of ammonia. Nickel is used in the hydrogenation of oils. Formation of interstitial compounds: Interstitial compounds are compounds of indefinite structure and composition. They are formed by the incorporation of small atoms like hydrogen, boron, carbon or nitrogen in the spaces between the metal atoms, that is, the interstices of the lattice. These substances are also known as non-stoichiometric substances. EX: Fe0.94O, TiC, Mn4N, Fe3H, VH0.56 and TiH1.7. The important physical and chemical Characteristics of these compounds are: They are extremely hard; some borides approach diamond in hardness. They have higher melting points than those of pure metals. They are chemically inert. They possess good electrical conductivity. Alloy formation: An alloy may be defined as a homogeneous mixture of a metal with other metals or metalloids, and sometimes even a non-metal. The atomic radii of the transition elements in any series are not too different from each other. As a result, they can very easily replace each other in the lattice, and thus, readily form alloys. Alloys are classified according to their components into two distinct types, namely, ferrous and non-ferrous. Ferrous alloys: Ferrous alloys contain iron, carbon, and one or two of the other elements like chromium, vanadium, tungsten and molybdenum. Non-ferrous alloys: These alloys do not contain iron as one of the components. The number of non-ferrous alloys used in technology is very large. EX: aluminium-bronze, duralumin magnalumin and electron. Brass an alloy of copper and zinc, and bronze, an alloy of copper and tin, are also important non-ferrous alloys.

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