Notes On Werner's Theory - CBSE Class 12 Chemistry
Werner's Theory: Alfred Wernera Swiss chemist put forward a theory to explain the formation of complex compounds. It was the first successful explanation,became famous as the coordination theory of complex compounds, which is also known as Werner's theory. Postulates: (a) The central metal atom (or) ion in a coordination compound exhibits two types of valencies - primary and secondary. (b) Primary valencies are ionisable and correspond to the number of charges on the complex ion. Primary valencies apply equally well to simple salts and to complexes and are satisfied by negative ions. (c) Secondary valencies correspond to the valencies that a metal atom (or) ion exercises towards neutral molecules (or) negative ions in the formation of its complex ions. (d) Secondary valencies are directional and so a complex has a particular shape. The number and arrangement of ligands in space determines the stereochemistry of a complex. The postulates of Werner's coordination theory were actually based on experimental evidence rather than theoretical. Although Werner's theory successfully explains the bonding features in coordination compounds, it has drawbacks. Drawbacks: It doesn't explain why only certain elements form coordination compounds. It does not explain why the bonds in coordination compounds have directional properties. It does not explain the colour, and the magnetic and optical properties of complexes.

Summary

Werner's Theory: Alfred Wernera Swiss chemist put forward a theory to explain the formation of complex compounds. It was the first successful explanation,became famous as the coordination theory of complex compounds, which is also known as Werner's theory. Postulates: (a) The central metal atom (or) ion in a coordination compound exhibits two types of valencies - primary and secondary. (b) Primary valencies are ionisable and correspond to the number of charges on the complex ion. Primary valencies apply equally well to simple salts and to complexes and are satisfied by negative ions. (c) Secondary valencies correspond to the valencies that a metal atom (or) ion exercises towards neutral molecules (or) negative ions in the formation of its complex ions. (d) Secondary valencies are directional and so a complex has a particular shape. The number and arrangement of ligands in space determines the stereochemistry of a complex. The postulates of Werner's coordination theory were actually based on experimental evidence rather than theoretical. Although Werner's theory successfully explains the bonding features in coordination compounds, it has drawbacks. Drawbacks: It doesn't explain why only certain elements form coordination compounds. It does not explain why the bonds in coordination compounds have directional properties. It does not explain the colour, and the magnetic and optical properties of complexes.