Question -
Answer -
WernerтАЩs postulates explain the bonding incoordination compounds as follows:
(i)┬аA metal exhibits two types of valencies namely,primary and secondary valencies. Primary valencies are satisfied by negative ionswhile secondary valencies are satisfied by both negative and neutral ions.
(In modern terminology, the primary valencycorresponds to the oxidation number of the metal ion, whereas the secondaryvalency refers to the coordination number of the metal ion.
(ii)┬аA metal ion has a definite number of secondaryvalencies around the central atom. Also, these valencies project in a specificdirection in the space assigned to the definite geometry of the coordinationcompound.
(iii)┬аPrimary valencies are usuallyionizable, while secondary valencies are non-ionizable.