Werner's coordination theory

 

The important postulates of Werner's theory of coordination compound are:
1. Metals possess two different sports of valency:  primary or ionizable valency and secondary or non-ionizable valency.
2. The central metal atom has a fixed number of secondary valencies (that is the coordination number), e.g., Co (lll) or Pt-(lV) have six secondary valencies while Cu (ll) or Pd (ll) have four secondary valencies.
3 . Primary valencies are satisfied by only -ve ions while secondary valencies may be satisfied by -ve ions or neutral molecules.
4 . Having established the number of secondary valencies, Werner attempted to find the shape of the complex. For example, six secondary valencies, are directed towards the corners of a regular octahedron, four secondary valencies are directed towards the four corners of a square-planar or tetrahedral.