Coordination Compounds — Chemistry STD 12 Science — Question

Metals possess two types of valencies called

Primary valency which are ionisable;

secondary valency which are non- ionisable

Primary valency is satisfied by the negative ions and it is that which a metal exhibits in the formation of its simple salts.

Secondary valencies are satisfied by neutral ligand or negative ligand and are those which metal exercises in the formation of its complex ions. Every cation has a fixed number of secondary valencies which are directed in space about central metal ion in certain fixed directions, e.g,, In $CoCl_3-6NH_3$, valencies between Co and Cl are primary valencies and valencies between Co and NH_3are secondary. In $COCl_3-6NH_3$, six ammonia molecules linked to Co by secondary valencies are directed to six corners of a regular octahedron and thus account for structure of $COCl_3-6NH_3$ as follows: