Brief concepts of Werner’s theory of coordination compounds
Alfred Werner studied the structure of coordination complexes and put forward his ideas in the year 1893 which were known as ‘Werner’s coordination theory.
Postulates of Werner’s theory
(i) Every metal atom has two types of valencies
- Primary valency or ionisable valency
- Secondary valency or non ionisable valency
(ii) The primary valency corresponds to the oxidation state of the metal ion.
The primary valency of the metal ion is always satisfied by negative ions.
(iii) Secondary valency corresponds to the coordination number of the metal ion or atom. The secondary valencies may be satisfied by either negative ions or neutral molecules.
(iv) The molecules or ion that satisfy secondary valencies are called ligands.
(v) The ligands which satisfy secondary valencies must project in definite directions in space. So the secondary valencies are directional in nature whereas the primary valencies are non-directional in nature.
(vi) The ligands have unshared pair of electrons. These unshared pair of electrons are donated to central metal ion or atom in a compound. Such compounds are called coordination compounds.