(a) Account for the following: (i) Copper (I) compounds are white whereas Copper (II) compounds are coloured. (ii) Chromates change their colour when kept in an acidic solution. (iii) Zn, Cd, Hg are considered as d-block elements but not as transition elements. (b) Calculate the spin only moment of Co^(2+)(Z=27) by writing the electronic configuration of Co and Co^(2+).

(a) Account for the following: (i) Copper (I) compounds are white whe

1.	(a) Account for the following: (i) Copper (I) compounds are white whereas Copper (II) compounds are coloured. (ii) Chromates change their colour when kept in an acidic solution. (iii) Zn, Cd, Hg are considered as d-block elements but not as transition elements. (b) Calculate the spin only moment of Co^(2+)(Z=27) by writing the electronic configuration of Co and Co^(2+).
Answer» Solution :(a) (i) ELECTRONIC configurationof `Cu^(+)` is …. `3d^(10)`. The d-subshells are completely filled. No transition of electrons takes place between the d-orbitals. Hence, no colour. (ii) When CHROMATES are kept in an ACIDIC solution, it changes into dichromate. While chromates are yellow in colour, dichromates are ORANGE. `underset("Yellow")(2Na_(2)CrO_(4))+2H^(+) to underset("Orange")(Na_(2)Cr_(2)O_(7))+2Na^(+)+H_(2)O` (iii) Zn, Cd and Hg have completed d-orbitals in the outer shells. They don.t fit into the definition of transition elements which have incomplete d-orbitals of the inner shell. However, for the sake of convenience, they are placed in d-block elements. (b) Electronic configuration of `Co=3d^(7)4s^(2)` Electronic configuration of `Co^(2+)=3d^(7)` Number of unpaired electrons = 3 `mu=sqrt(3(3+2))=sqrt(3xx5)` `=sqrt(15)=3.87`