what is werner's theory
Answers
Answer:
Alfred Werner in 1893 put forward his concept of auxiliary (secondary) valency for advancing a correct explanation for the characteristics of the coordination compounds.
Explanation:
The fundamental postulates of Werner's theory which was actually a result of dream and made Werner a noble prize winner in chemistry may be summarized as below.
1. Metals possess two types of valencies, namely primary (principal) or ionizable valency and secondary (auxiliary) or non–ionizable valency.
Primary valencies are those which a metal normally exhibit in the formation of its simple salts. Thus, in the formation of PtCl4, CuSO4 and AgCl the primary valencies of Pt, Cu and Ag are 4, 2 and 1 respectively. Primary valencies are satisfied by negative ions.
Secondary Valencies are those which a metal cation exercises towards a neutral molecule or negative group in the formation of its complex ions. Thus, secondary valencies may be satisfied by negative ions, neutral molecules having lone electron pair (e.g., H2O, NH3, etc.) or even sometimes by some positive groups. In every case, the coordination number of the metal must be fulfilled.
2. Every metal has a fixed number of secondary valencies, e.g., cobalt3+ and platinum4+ were recognized to have six secondary valencies and copper2+ four. The total number of secondary valencies required by a metal is more commonly known as coordination number (C.N).
3. The secondary valencies are always directed towards fixed positions in space about the central metal ions. Thus, the number and arrangement of ligands in space determines the stereochemistry of a complex. Thus, in case of six secondary valencies the arrangement of secondary valencies may be as directed to the apices of a regular octahedral while in case of four secondary valencies arrangement might be either a planar or a tetrahedral manner and thus, this postulate predicted the possibilities of a variety of type of isomerism in coordination compounds. Remember that primary valencies are non–directional.
Explanation:
They are the primary and secondary valency. The primary valency relates to the oxidation state and the secondary valency relates to the coordinate number. The number of secondary valences is fixed for every metal atom. It means that the coordination number is fixed.
Limitations of Werner's Theory :-
It fails to explain the magnetic, colour and optical properties shown by coordination compounds. It failed to explain the reason why all elements don't form coordination compounds. It failed to explain the directional properties of bonds in coordination compounds.
