What NEET Asks
- Direct questions on identifying ligand types (monodentate, bidentate, polydentate).
- Determining coordination number based on the denticity of ligands.
- Questions involving common examples of chelating ligands like 'en', 'ox', and 'EDTA'.
Key Points
- Ligands: Species (ions or molecules) that donate electron pairs to a central metal atom/ion to form coordinate bonds.
- Denticity: The number of donor atoms in a ligand that can form coordinate bonds with the central metal atom/ion.
- Monodentate Ligands: Ligands with one donor atom, forming one coordinate bond. Examples: H₂O, NH₃, Cl⁻, CN⁻, OH⁻.
- Bidentate Ligands: Ligands with two donor atoms, forming two coordinate bonds. Examples: Ethylenediamine (en), Oxalate ion (C₂O₄²⁻), Glycinate ion.
- Polydentate Ligands: Ligands with more than two donor atoms, forming multiple coordinate bonds. Examples: Diethylenetriamine (triamine, tridentate), EDTA (hexadentate).
- Chelating Ligands: Bidentate or polydentate ligands that bind through two or more donor atoms to the same metal ion, forming stable ring-like structures (chelates).
Must-Know Formula / Reaction
Denticity = Number of donor atoms from a single ligand.
- Denticity directly determines the number of coordinate bonds formed by that ligand. For instance, a bidentate ligand contributes 2 to the coordination number.
Common Mistakes
- Students often confuse denticity with the overall charge of the ligand. Denticity is about donor atoms, not charge.
- Misidentifying the donor atoms within complex ligands like EDTA or glycinate.
- Forgetting that ambidentate ligands are still monodentate, as they only bind through one donor atom at a time.
Rapid Revision
Remember: Monodentate (1 bond), Bidentate (2 bonds), Polydentate (>2 bonds). Chelating ligands form rings and increase stability. Focus on common examples for each type to quickly solve identification questions.