Chelate ligands, like EDTA⁴⁻, use two or more donor atoms simultaneously to bind a metal ion, forming more stable complexes than those with unidentate ligands. The denticity of the ligand is the number of such ligating groups.

Unidentate ligands, like Cl⁻ or H₂O, bind through a single donor atom. Didentate ligands, such as ethane-1,2-diamine or oxalate, bind through two donor atoms. Polydentate ligands, like N(CH₂CH₂NH₂)₃, have several donor atoms in a single ligand.

Ligands are ions or molecules bound to the central atom/ion in a coordination entity. They can be simple ions like Cl⁻, small molecules like H₂O or NH₃, or even larger molecules such as proteins. Examples include Cl⁻, H₂O, NH₃, H₂NCH₂CH₂NH₂, ...

The central atom/ion is the one to which a fixed number of ions/groups are bound in a definite geometric arrangement. Examples are Ni²⁺ in [NiCl₂(H₂O)₄], Co³⁺ in [CoCl(NH₃)₅]²⁺, and Fe³⁺ in [Fe(CN)₆]³⁻, also referred to as Lewis acids.

A coordination entity consists of a central metal atom or ion bonded to a fixed number of ions or molecules. Examples include [CoCl₃(NH₃)₃], [Ni(CO)₄], [PtCl₂(NH₃)₂], [Fe(CN)₆]⁴⁻, and [Co(NH₃)₆]³⁺.