WERNER'S THEORY By:PUSHPALATHA BUDUMURU
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WERNER,S THEORY Metals possess two types of valencies Primary / principal / ionizable valency Secondary / auxillary / non-ionizable valency Primary valency corresponds to oxidation number For example, in the formation of PtCl4 the primary valency of Pt is 4 Primary Valency is satisfied by negative ions
Secondary valency corresponds to coordination number Secondary valencies are satisfied by negative ions, neutral molecules or even some positive groups. Primary valencies are shown by dotted lines and secondary valencies are shown by thick lines. primary valencie.. secondary valencies
Primary Valencies are Non-Directional where as secondary Valencies are Directional To distinguish between the two types of Valencies, werner introduced the square brackets The portion enclosed in the bracket is coordination sphere and the portion present out side the bracket as ionising sphere
Thus according to Werner theory, the compound CoCl 6NH3 written as [Co(NHC. Six ammonia molecules satisfy the six secondary valencies of cobalt. They are directly attached to the cot So they are shown by thick lines. 9 The oxidation state of cobalt is +3, d cNH2 satisfied by three chloride ions These are shown by dotted lines. H2 It can be represented as here:
The three chloride ions present in ionising sphere are loosely bound Therefore the total number of ions 1+3 4 Let us take another complex of coCl3 with NHais COCl3.5NH, To satisfy the six secondary valencies of cobalt, one chloride ion must be present inside the coordination sphere.
Thus the six secondary valencies (5 by ammonia and one satisfied by CI) are shown by thick lines The three primary valencies of cobalt are satisfied by three chloride ions, these are shown by dotted lines Here one chloride ion assumes a Dual behaviour. Hence such chloride ion is shown d_...co d by both thick and dotted lines irn the structure Nia NH3
Thus the complex COC.5NH2 will ionise in solution as below 3* On ionisation it forms 3 ions .Similarly, the compound COCI2.4NH formulated as 3* [Co(NH)Cl,]Cl and on ionisation forms two ions
Applications: It predicts the exact structure of each complex. .It explains why a particular metal and particular ligand form different complexes. It also explains the different properties of each complex It predicts the structure of different complexes with coordination number 4 and 6 .
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