Donor Atom
Definition and meaning of Donor Atom in chemistry.
A donor atom is the atom within a ligand that has a lone pair of electrons and forms a coordinate (dative) covalent bond by donating that pair to a central metal ion in a coordination complex.
In more detail
Common donor atoms include nitrogen, oxygen, sulfur, phosphorus, and the halogens, each acting as a Lewis base toward the metal, which acts as a Lewis acid. Ligands are classified by how many donor atoms they use at once: monodentate ligands bind through a single donor atom, while polydentate (chelating) ligands, such as EDTA, use several donor atoms simultaneously to form ring structures called chelate rings. The identity, number, and arrangement of donor atoms largely determine a complex's coordination number, geometry, and thermodynamic stability.
Key facts
| Field | Inorganic Chemistry |
|---|---|
| Typical donor atoms | N, O, S, P, halogens |
| Bond formed | Coordinate (dative) covalent bond |
| Multiple donor atoms | Chelating (polydentate) ligands, e.g., EDTA |
In the complex ion [Cu(NH3)4]2+, each ammonia ligand binds to copper through the lone pair on its nitrogen atom, so nitrogen is the donor atom, forming four coordinate bonds to the central Cu2+ ion.
Frequently asked questions
What is the difference between a donor atom and a ligand?
A ligand is the entire molecule or ion that attaches to a metal; the donor atom is the specific atom within that ligand that actually supplies the lone pair of electrons forming the bond to the metal.
Can one ligand have more than one donor atom?
Yes. Polydentate (chelating) ligands such as EDTA or ethylenediamine contain multiple donor atoms that bind simultaneously to the same metal ion, creating stable ring structures called chelate rings.