• In 1893 Werner produced a theory of coordination compound to explain the structure  and formation of compound.
  • Werner was the first inorganic chemist to be awarded Nobel prize for chemistry in1913
  • Werner postulated that metal exhibits two type of valancies i.e. 
                                          (1)Primary valancy and 
                                          (2)Secondary valancy 

Primary valency:

  • The ligands which satisfy primary valency always ionic in nature.
  • Primary valency is ionizable and non directional.
  • Primary valency only satisfied by negative ions i.e. anions and are written outside the coordination sphere.
  • Primary valency donot decide geometry of the coordination compound.
  • Primary valency corresponds to the oxidation state of the metal ion.
  • Primary valency is represented by dotted line i.e.(……….)

Secondary valency:

  • The ligands which satisfy secondary valency always covalent in nature.
  • Secondary valency is non ionizable and directional.
  • Secondary valency is satisfied by either neutral or negative or both type of ligands.
  • Secondary valency decide geometry of the complex 
  • Secondary valency corresponds to the coordination number of the metal ion.
  • Secondary valency is represented by solid line.

Question for you:

      In [Co(NH3)4Cl2]Cl   chlorine ligand satisfies which type of valency.

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