State any three postulates of Werner theory of co-ordination compounds? 

Explanation

i. In coordination compounds, metal central metal atom or ion exhibit two types of valencies. Primary valency (ionisable valency) and Secondary valency (nonionisable valency)
ii. Primary valency of a metal is the charge on the metal and secondary valency is its coordination number of the complex ion that is the number of covalent bonds formed by ligands with central metal ion.
iii. Primary valencies of a metal ion are satisfied by negative ions and the secondary valency is satisfied by negative ions or neutral molecules which act as ligands.
iv. The secondary valency of a metal is arranged in space to give a definite geometrical shape to the complex depending on the number of ligands.