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CIE A Level Chemistry復習筆記6.2.4 Ligands

Category: A-level課程, 教材筆記, 福利干貨 Date: 2022年8月15日下午3:00

A?ligand?is a molecule or ion that has?one?or?more?lone pairs of electrons
These lone pairs of electrons are donated by the ligand, to form?dative covalent bonds?to a central metal atom or ion

Examples of ligands table

6.2-Chemistry-of-Transition-Elements-Examples-of-ligands-table

6.2-Chemistry-of-Transition-Elements-Ligand-Complex-Example

Example of a complex formed between a transition metal ion (Fe²⁺) and a ligand (H₂O) by dative covalent bonds

Different?ligands?can form different numbers of dative bonds to the central metal ion in a complex.
- Some ligands can form?one?dative bond to the central metal ion
- Other ligands can form?two?dative bonds, and some can form?multiple?dative bonds

Monodentate?ligands can form only?one?dative bond to the central metal ion
Examples of monodentate ligands are:
- Water (H₂O) molecules
- Ammonia (NH₃) molecules
- Chloride (Cl^-) ions
- Cyanide (CN^-) ions

6.2-Chemistry-of-Transition-Elements-Monodentate-Ligands

Examples of complexes with monodentate ligands

Bidentate?ligands can each form?two?dative bonds to the central metal ion
This is because each ligand contains?two?atoms with lone pairs of electrons
Examples of bidentate ligands are:
- 1,2-iaminoethane (H₂NCH₂CH₂NH₂) which is also written as?‘en’
- Ethanedioate ion (C₂O₄^2-?) which is sometimes written as?‘ox’

6.2-Chemistry-of-Transition-Elements-Bidentate-Ligands

Examples of complexes with bidentate ligands

Some ligands contain more than two atoms with lone pairs of electrons
These ligands can form more than two dative bonds to the and are said to be?polydentate?ligands
An example of a polydentate ligand is EDTA^4-?, which is a?hexadentate?ligand as it forms 6 dative covalent bonds to the central metal ion

Example of a polydentate ligand complex