Ligands are the neutral molecules, anions or cations which are directly linked to the central metal atom or ion in a complex ion. Monodentate ligand: They have one donor atom i.e., they donate only one electron pair to the central atom or ion. Examples are F−,Cl−,Br−,H2O,etc. Bidentate ligand: The ligands which have two donor atoms i.e., they donate two electron pairs.
Ethylene diamine has the formula: H2N..−CH2−CH2−N..H2 , and it contains two donor atoms. So, it is a bidentate ligand.