ACS Analytical Chemistry Complete Practice Exam 2026

EDTA binds metals through multiple donor sites, making it a hexadentate ligand. It has two nitrogen atoms and four carboxylate oxygens that can donate lone pairs to a metal ion, giving six potential bonds. In its deprotonated form, these six donor atoms coordinate to the metal, effectively wrapping around it to form a highly stable chelate complex. This is why EDTA is described as hexadentate with six lone-pair donors. Monodentate, bidentate, or tetradentate describe ligands that offer only one, two, or four donor sites, respectively, which is not the case for EDTA.