Explain the terms
Ligand

Explanation

Ligand : The ions or molecules bound to the central atom/ion in the coordination entity are called ligands. These may be
a) simple ions such as `Cl^(-)`
b) small molecules such as `H_(2)O" or "NH_(3)`
c) large molecules such as `H_(2)NCH_(2)CH_(2)NH_(2)" or "N(CH_(2)CH_(2)NH_(2))_(3)` or even (d) macro-molecules, such as proteins.
On the basis of the number of donor atoms available for coordination, the ligands can be classified as :
a) Unidentate : One donor atom, `Eg. : overset(..)NH_(3), :overset(..)underset(..)Cl:` etc.
b) Bidentate : Two donor atoms, `Eg. : H_(2)NCH_(2)CH_(2)NH_(2)`
(ethane-1,2-diamine or en), `C_(2)O_(4)^(2-)` (oxalate), etc.
c) Polydentate : More than two donor atoms Eg. `:N(CH_(2)CH_(2)NH_(2))_(3))` EDTA. etc.