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 seconda/y valencies are directed in space which determines the shape of the complex.

In Werner.s representation, dotted lines represent, primary valency whereas thick lines repre$ent secondary valency. Some negative ligands, depending upon the complex, may satisfy both .primary and secondary valencies. Such ligands do not ionise.
( iv) Primary valencies are ionisable valencies. Secondary valencies arenon-ionisable valencies