Question

Write the postulates of Werner's theory of co-ordination complexes.

Hint:

The number of secondary valencies is constant for a metal in a specific oxidation state.

Answer 1

Step 1: Understanding the Concept:
Alfred Werner proposed the first theory to explain the structures and properties of coordination compounds.
Step 2: Detailed Explanation:
The main postulates are:
1. Two types of Valencies: Metals in coordination compounds show two types of linkages: Primary and Secondary.
2. Primary Valency: It is ionizable and corresponds to the oxidation state of the metal. It is satisfied by negative ions.
3. Secondary Valency: It is non-ionizable and corresponds to the coordination number. It is satisfied by negative ions or neutral molecules (ligands).
4. Spatial Arrangement: Secondary valencies are directed toward fixed positions in space, giving a definite geometry to the complex (e.g., octahedral, tetrahedral).
Step 3: Final Answer:
Werner's theory identifies ionizable primary valency (oxidation state) and non-ionizable, directional secondary valency (coordination number).