Class 12 Chemistry Coordination Compounds Denticity


 it determines  the total number of donor atoms in a molecule.

On the basis of the property denticity ligands are :

  • Monodentate /unidentate: is that which has one donor atom

Examples : CN-, OH-,Cl-,Br-,NH3:,H2O,CO etc


  • Di-dentate: if it has two donor atoms





(ethylene diamine )


  • Polydentate : if it has 3 or more donor atoms in it DIETHYLENE TRIAMINE (tridendate)



Hexadentate: ethylene diamine tetra acetic acid (EDTA)


chelate: when the ligand has two or more donor atoms and they are arranged in such a way that they give rise to a ring like structure than the effect is called chelating and the ring formed is chelate .

For example:


uses of chelates:

  • They are used in softening of hard water
  • In qualitative analysis for detection of metal
  • In separation of lanthanoids and actinoids


Ambidentate ligand: that have two donor atoms but doesn’t show chelation. This group bond at a time by one atom.

            For example: CN-,NO2 etc


Symmetrical and unsymmetrical ligands :

Symmetrical ligands: if ligands attached to central atom are of same type

Example: ethylenediamine etc.


Unsymmetrical ligands: if ligands attached are of different type.


Example: glycinate ion etc.

Coordination number: it is the number of ligands bonded with the central metal atom for example: IN [Ag (CN)2]-“the no. Of ligands attached are 2 therefore coordination no. is 2 “.

Oxidation number: it is the residual chargeleft on the atom when all other atoms are removed from it .it is calculated by assigning appropriate charges to ligands and then equating the sum of the charges on the central atom and the ligands equal to the charge on the coordination sphere.

For example: [Co (NH3)6] Cl3 in this oxidation state of NH3 is 0 and for Cl is -1, and ooxidation state of Co is taken as x then

                               (x-3)  x 1=0 or       x=+3

        another example: [Cu (CN)4]3- in this oxidation state of Cu is taken as x, CN as -1 so,

                                x + (-1  X 4) = -3 or x=+1


Homo-leptic and hetero-leptic compounds

Homoleptic: are those which have same kind of ligands attached to central metal atom

Example:in [Co (NH3)6] Cl3 is homoleptic as ligands are same

 terolyptic: when ligands attached are of different type

Example: in [CoCl3(NH3)3]3+ is heterolytic because ligands attached are of different types.


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