Explain Werner's theory. Give the Werner's structures of `CoCl_3. 6NH_3 , CoCl_3 . 5NH_3, CoCl_3 . 4NH_3` and `CoCl_3 . 3NH_3` .

Explanation

Werner proposed two types of valencies to explain the formation and the structure of these complex compounds.
i) The primary valence: This corresponds to the oxidation state of the central transition metal ion in the complex compounds. This primary valence is satisfied by a negative ion only in the complex compound.
ii) Secondary valence: This is equal to the number of chemical groups bound to central metal ion. The no. of secondary valencies is called co-ordination number of the metal.
iii) These secondary valencies are directed in space which determines the shape of the complex.


In werner.s representation, dotted lines represent primary valency whereas thick lines represent secondary valency. Some negative ligands, depending upon the complex, may satisfy both primary and secondary valencies. Such ligands do not lonise.
iv) Primary valencies are ionisable valencies. Secondary valencies are non-ionisable valencies.