In 1893 Werner produced a theory to explain the structures, formation and nature of bonding in the coordination compounds. This theory is known as Werner’s theory of coordination compounds.
Postulates of Werner's Theory:
The important postulates as observed by Alfred Werner throughout his experiments are as follows:
- The complex/ coordination compounds contain a central metal atom.
- The metal atoms in a coordination compound generally show two types of valency: primary valency and secondary valency.
- The primary valencies denote the oxidation state. They are ionizable and are satisfied by the negative ions.
- Secondary valencies denote the coordination number. They are non-ionizable and are fixed for every metal atom. The secondary valency is generally satisfied by the neutral molecules or negative ions.
- The metal atoms should satisfy both primary and secondary valencies.
- The secondary valency of the atom basically shows the geometry/ polyhedra of the particular coordination compound.
Limitations of Werner’s Theory:
- Though Werner explained some properties of the coordination compound, he failed to explain the colour of the coordinate compound.
- He could not explain the magnetic and optical properties of coordination compounds.
- He could not answer the question, why does the coordination sphere have a definite geometry.