Metal Chelate Complexes
EDTA Titration Curves
Metal Ligand Complexes 

Concept #1: Ligands act as Lewis bases and monodentate ligands possess 1 element that can donate a lone pair. 

Concept #2: Bidentate ligands possess 2 electron donating elements within their structures. 

Concept #3: Polydentate Ligands possess more than 2 electron donating elements and are readily used in metal complex titrations.