1. Postulates of Werners Coordination theory:
(i) Primary Valency (Ionizable Valency):
- Primary Valency of a central metal atom is equal to the oxidation state of the central metal atom.
- The primary Valency of the central metal atom can be satisfied by negative species.
- Primary Valency exhibiting species being non-directional in nature.
- All primary Valency exhibiting the species cannot retain their individual identity.
- Bonding of primary valencies exhibiting the species with the central metal atom is denoted by dotted(———) lines.
(ii) Secondary Valency (Non-Ionizable Valency) :
- Secondary valency of the central metal atom is equal to coordination number of the central metal atom.
- The secondary valency can be satisfied by negative, positive, or neutral species.
- Secondary valency exhibiting the species being directional in nature.
- The Secondary valency is responsible for the geometry of the complex as:
- Secondary valency exhibiting species can retain their individual identity
- Bonding of secondary Valency exhibiting the species with the central metal atom is denoted by a solid line ( –).
- Some of the negatively charged species can satisfy primary as well as secondary valency, such negative charged species and their bonding with the central metal atom is denoted by solid as well as dotted lines.
2. Limitations of Werner’s coordination theory:
- Werner’s coordination theory was failed to explain the bonding nature between the central metal atom and the ligands.
- Werner’s coordination theory was failed to explain the geometry of complexes when secondary valency being equal to 4.
This is how we have discussed Werners coordination theory & its limitations.