Question

Explain the bonding in coordination compounds in terms of Werner’s postulates.

Answer 1

Hint: Coordination compounds consist of multiple or one metal centre that is attached to ligands that have the tendency to donate electrons to the metal. The coordination compounds can be neutral or charged

Complete step by step answer:
For explaining the nature of bonding and the structure of the compounds, Werner has proposed a theory known as Werner’s theory in $1893$ . In this theory, he has given postulates which are as follows:


1.In coordination compounds, metal atoms show two types of valencies which are primary and secondary valencies. The primary valencies which are shown are ionizable, whereas on the other hand, the secondary valencies are non-ionizable. The primary valency corresponds to oxidation state, whereas secondary valency corresponds to coordination number.

2.In coordination compounds, each metal atom has a fixed number of secondary valencies that is fixed coordination number.

3.Here, the metal atom satisfies both primary valencies as well as secondary valencies. Here, primary valencies are satisfied from negative ions and secondary valencies are satisfied from neutral or negative molecules.

4.In coordination compounds, secondary valency is always directed towards the fixed position in space which makes the geometry definite in a coordination compound. Let us take an example, if a metal has four valencies, then these are arranged in either square planar arrangement or tetrahedral arrangement around the central ion. The stereochemistry of the complex compounds is determined by secondary valencies.

Note: Werner has given a theory named as Werner’s theory in $1893$ where he describes the structure and foundation of complex compounds.

There are some limitations of Werner’s theory and they are as follows:
1. He failed to explain the directional properties of the bonds.
2. He failed to explain the color, optical and magnetic properties of the compounds.