Werners theory of coordination compound

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Werner's theory of coordination compounds:-

In the year 1893, Alfred Warner, studied the structure of coordination compounds , such as CoCI³6NH³ and CuSO⁴ 4NH³ and proposed a theory of coordination compounds which is commonly known as Werners coordination theory .  The major postulates of this theory are as follows -

1- A metal in coordination compound possesses two types of valence , i.e., (a) primary or principal valence which corresponds to it's oxidation number . (b) Secondary or residual or auxiliary valence which corresponds to it's coordination number.

    The primary valence is ionisable where secondary valence is non - ionisable . For example , in the complex CoCI³6NH³, the primary valence of Co is three and secondary valence of Co is 6.

2- Every metal atom has a tendency to satisfy both it's primary and secondary valences. The primary valence are satisfied by negative ions where secondary valences is satisfied by -ve ions or neutral molecules .As -ve ions often satisfy both primary as well as secondary valencies , such dual behavior valence are not ionised .

3- Each metal atom has a fixed number of secondary valencies which are directed towards fixed position in space and thus it gives the geometry or shape of the complex . On the other hand primary valencies are non-directional.

For example , 

                          If a central metal ion or atom has six secondary valencies , there are arranged octahedraly around the central metal atom or ion. If the central metal ion or atom has four secondary valencies , these have either tetrahedral or square planar arrangement around the central metal atom or ion .

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