Question

What is primary and secondary valency in coordination compounds with examples?

Answer 1

As we know that primary valencies and secondary valencies in coordination compounds are the postulates of Werner’s theory. Primary valencies help us in finding the oxidation state and charge whereas secondary valencies help us in finding the coordination number of the complex.

Complete answer:
Let us understand the concept of primary and secondary valencies along with the examples as follows:-
-We know that primary and secondary valencies are among the postulates of Werner’s theory. According to this theory, the central metal atom of the coordination complexes shows two types of valencies that are primary valency and secondary valency.
-Primary valency: It is referred to the number of negative ions which are equivalent to the charge on the metal ion. It can also be said as the oxidation state of the central metal atom.
-Secondary valency: It is referred to the number of ions of molecules that are coordinated to the metal ion or we can say that it is the number of ligands attached or coordinated to metal ions. It relates to the coordination number of the central metal atom.
-For example the compound is ${{K}_{4}}[Fe{{(CN)}_{6}}]$:-
Here the primary valency of Fe is +2 and the secondary valency or coordination number of Fe is 6 (as we can see that 6 $C{{N}^{-}}$ ligands are attached to the central metal atom.

Note:
-To solve such types of questions, you must study and learn the concepts of coordination chemistry.
-Also primary valencies are ionisable whereas secondary valencies are non-ionisable.
-The ligands attached to the central metal atom are projected in space to give the shape of the complex.