decribe briefly primary valence and secondary valence.

In coordination compound, primary valence is the number of negative ions which are required to satisfy the charge on the metal ion while secondary valence are those which satisfy the coordination number of central metal ion. Primary valence is ionisable and variable while secondary valence is non ionisable.

Coordination number may be defined as number of mono dentate or equivalent ligand attached to central metal ion. For example: Coordination number in K4[Fe(CN)6], the coordination number is 6, in [Cr(C2O4)3]-3, coordination number is 6.


Example: [Cr(H2O)6]Cl3 = Primary valency is Chloride ion.

Secondary valency is H2O molecules.

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  • The primary valences are ionisable, and are satisfied by negative ions.

  • The secondary valences are non-ionisable, and are satisfied by negative ions or neutral molecules. The secondary valence is equal to the coordination number of a metal, and remains fixed for a metal.

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