Example 4.8

Example . Sc colourless Ti + colourless Ti purple + blue green violet violet violet blue pink yellow green 3d Co + Co bluepink Ni green Cu blue Zn colourless Configuration Example Colour Table . : Colours of Some of the First Row (aquated) Transition Metal Ions . . Formation of Complex Compounds . Calculate the ‘spin only’ magnetic moment of M (aq) ion ( Z = ). When an electron from a lower energy d orbital is excited to a higher energy d orbital, the energy of excitation corresponds to the frequency of light absorbed (Unit ). This frequency generally lies in the visible region. The colour observed corresponds to the complementary colour of the light absorbed. The frequency of the light absorbed is determined by the nature of the ligand. In aqueous solutions where water molecules are the ligands, the co lours of the ions observed are listed in Table . . A few coloured solutions of d –block elements are illustrated in Fig. . . . . Formation of Coloured Ions Fig. . : Colours of some of the first row transition metal ions in aqueous solutions. From left to right: V + ,V + ,Mn + ,Fe + ,Co + ,Ni + and Cu + . Complex compounds are those in which the metal ions bind a number of anions or neutral molecules giving complex species with characteristic properties. A few examples are: [Fe(CN) ] – , [Fe(CN) ] – , [Cu(NH ) ] + and [PtCl ] – . (The chemistry of complex compounds is dealt with in detail in Unit ). The transition metals form a large number of complex compounds. This is due to the comparatively smaller sizes of the metal ions, their high ionic charges and the availability of d orbitals for bond formation. The transition metals and their compounds are known for their catalytic activity. This activity is ascribed to their ability to adopt multiple oxidation states and to form complexes. Vanadium(V) oxide (in Contact Process), finely divided iron (in Haber’s Process), and nickel (in Catalytic Hydrogenation) are