what is the difference btw primary and secondry valency?
Primary valency may be defined as +ve charge raised over central metal ion as its oxidation state
Secondary valency may be defined as no of mono dentate or equivalent to mondentate ligand attached to central metal ion. It defines the Coordination No.
It is ionisable and variable
It is non ionisable and fixed
Example: [Cr(H2O)6]Cl3 = Primary valency is satisfied by Chloride ion and is equal to 3.
Secondary valency is satisfied by H2O molecules and is equal to 6.