Classification of Ligands with Examples and Tips to Identify Them
Ligands and Its Types form a central part of JEE Main Coordination Chemistry. A ligand is any ion or molecule that donates a pair of electrons to a central metal atom or ion, forming a coordinate (dative covalent) bond and producing a coordination compound. Ligands influence the structure, colour, stability, and reactivity of complexes, making their study essential for cracking questions on coordination compounds in JEE Main.
Ligands are covered in-depth in NCERT and JEE Main syllabi. In complex formation, the ligand acts as a Lewis base (electron pair donor), while the metal acts as a Lewis acid (electron pair acceptor). Common examples include NH3, Cl-, H2O, and CN-. The number and nature of ligands attached define the geometry and chemical properties of the complex.
Classification of Ligands for JEE Main
Ligands are classified mainly by their number of donor atoms and how they bind. Understanding these types helps identify ligands rapidly in exams:
- Monodentate Ligand: Binds through a single donor atom (e.g. Cl-, NH3).
- Bidentate Ligand: Binds through two donor atoms (e.g. ethylenediamine, C2O42-).
- Polydentate Ligand: Binds through three or more donor atoms (e.g. EDTA4-).
- Chelating Ligand: Forms a ring by attaching to the same metal via two or more donor atoms.
- Ambidentate Ligand: Has more than one possible donor atom, binds through only one at a time (e.g. NO2- via N or O).
- Bridging Ligand: Connects two or more central metal atoms (e.g. OH- in [Cr2(OH)2(H2O)8]4+).
Examples of Each Ligand Type
| Ligand Type | Example Name | Formula |
|---|---|---|
| Monodentate | Ammonia | NH3 |
| Monodentate | Chloride ion | Cl- |
| Bidentate | Ethylenediamine | en |
| Bidentate | Oxalate | C2O42- |
| Polydentate | EDTA | EDTA4- |
| Ambidentate | Nitrite | NO2- |
| Bridging | Hydroxide | OH- |
Use this table to quickly revise ligand types for Coordination Compounds problems or MCQs involving examples.
Strong and Weak Ligands in the Spectrochemical Series
The strength of a ligand refers to its ability to split the d-orbitals of the metal ion: a strong ligand causes a large crystal field splitting (Δ0), while a weak ligand causes less splitting. The Spectrochemical Series arranges ligands from weak to strong field.
| Type | Ligand Name | Formula |
|---|---|---|
| Weak Ligands | Iodide, Bromide, Fluoride, Chloride | I-, Br-, F-, Cl- |
| Intermediate | Water, Ammonia, Oxalate | H2O, NH3, C2O42- |
| Strong Ligands | Cyanide, Carbonyl, Ethylenediamine | CN-, CO, en |
This ordering affects the colour and magnetic nature of compounds. For a deeper chart, visit the Spectrochemical Series page.
Tips to Identify Ligand Types in JEE Questions
- Count lone pairs and donor atoms; one = monodentate, two = bidentate, ≥3 = polydentate.
- If ligand forms a ring with metal, it is chelating (usually bi- or polydentate).
- If more than one possible donor, check if only one binds at a time (ambidentate).
- Ligands like NH3, Cl-, and H2O are always monodentate in JEE Main questions.
- Bridging ligands are often shown as μ (Greek letter mu) in complex formulas.
- Strong ligands (CN-, CO) create low-spin, usually colourless or pale colour complexes.
Practice identifying ligand types using these rules in sample complexes such as [Fe(CN)6]4- or [Ni(en)3]2+.
Summary Table: Ligands and Its Types for Quick Revision
| Ligand Type | Definition | Classic Example |
|---|---|---|
| Monodentate | One donor atom | NH3, Cl-, H2O |
| Bidentate | Two donor atoms | en, C2O42- |
| Polydentate | Three or more donor atoms | EDTA4- |
| Ambidentate | Two possible donor atoms, one at a time | NO2-, SCN- |
| Bridging | Connects two or more metals | OH-, Cl-, CN- |
This condensed chart boosts rapid revision for last-minute Coordination Compound practice papers and MCQ attempts.
JEE Main Application: Practice Questions on Ligand Types
- Which ligand is bidentate? (A) NH3 (B) Cl- (C) C2O42- (D) H2O
- Identify the strong field ligand: (A) H2O (B) F- (C) CO (D) I-
- Does [Fe(EDTA)]- contain a chelating ligand? Explain.
- Write the formula of a complex where en acts as bidentate ligand.
- True/False: SCN- can bind through either S or N atom.
For more MCQs and high-quality practice, try the Coordination Compounds Mock Test and read detailed explanations in the revision notes.
Understanding Ligands and Its Types is vital to mastering coordination chemistry for JEE Main. For naming rules, refer to the nomenclature of coordination compounds, and explore more examples to solidify your concept clarity. All content here is reviewed by JEE-expert faculty at Vedantu for accuracy and depth matching recent exam trends.
FAQs on Ligands and Their Types in Chemistry: Complete Guide
1. What is a ligand and its types?
Ligands are ions or molecules that donate a pair of electrons to a central metal atom to form a coordination compound. The main types of ligands include:
- Monodentate ligands: Attach through one donor atom (e.g., Cl−, NH3).
- Bidentate ligands: Have two donor atoms (e.g., ethylenediamine, C2O42−).
- Polydentate ligands: Bind through multiple donor atoms (e.g., EDTA).
- Ambidentate ligands: Can attach through two different atoms but only one at a time (e.g., NO2−, SCN−).
- Bridging ligands: Link two or more metal atoms (e.g., OH−, Cl−).
2. What are monodentate and bidentate ligands? Give examples.
Monodentate ligands donate one electron pair from a single donor atom, while bidentate ligands coordinate through two donor atoms simultaneously.
- Monodentate ligand examples: Cl−, NH3, H2O
- Bidentate ligand examples: ethylenediamine (en), oxalate ion (C2O42−)
3. What are the four strong ligands?
In the spectrochemical series, the four strongest ligands are:
- CN− (cyanide)
- CO (carbon monoxide)
- NO2− (nitrito)
- en (ethylenediamine)
These strong field ligands cause large splitting of the d-orbitals, often leading to low-spin complexes and can affect colour and magnetic properties.
4. How can I identify the type of ligand in a compound?
To identify the ligand type, count the number of donor atoms that can coordinate to the metal and observe their bonding pattern:
- Monodentate: Attaches via one atom (e.g., NH3).
- Bidentate: Two donor atoms present (e.g., en).
- Polydentate: Several donor atoms (e.g., EDTA has six).
- Ambidentate: Two possible sites but coordinates through one at a time (e.g., NO2− via N or O).
- Bridging: Binds multiple metals (look for μ-symbol in formula).
5. What is the difference between chelating and ambidentate ligands?
Chelating ligands possess two or more donor atoms and can simultaneously bind to a metal ion, forming a ring structure (chelate). Ambidentate ligands have two possible donor atoms but can bond through only one at a time, giving linkage isomerism.
- Chelating example: en (ethylenediamine), EDTA
- Ambidentate example: SCN− (can bind via S or N)
6. What is the basic ligand?
A basic ligand is one that carries a negative charge or can easily donate an electron pair, enhancing its ability to coordinate with metal ions. Examples include: OH−, Cl−, CN−.
7. List of ligands with examples and their types.
Here is a quick reference table of common ligands and their types:
- H2O: Monodentate
- NH3: Monodentate
- en (ethylenediamine): Bidentate/chelating
- C2O42− (oxalate): Bidentate
- EDTA: Polydentate (hexadentate)
- NO2−: Ambidentate
- Cl−: Monodentate/bridging
8. Why are strong ligands important for color and magnetism in complexes?
Strong ligands cause large d-orbital splitting in transition metal complexes, influencing their colour and magnetic properties. This leads to:
- Low-spin complexes (fewer unpaired electrons)
- Distinctive colours due to specific d-d transitions
- Helps in identifying coordination compound structure
9. Is water always a monodentate ligand?
Water acts as a monodentate ligand in almost all coordination compounds because it donates only one electron pair from its oxygen atom. It is rarely, if ever, polydentate under normal circumstances.
10. Can an ambidentate ligand coordinate through both atoms at the same time?
No, an ambidentate ligand can only coordinate through one donor atom at a time, not both simultaneously. For example, SCN− binds through either the sulfur or nitrogen, but not both together.
11. What are the three types of ligands?
The three primary types of ligands (based on number of donor atoms) are:
- Monodentate ligands: One donor atom (e.g., H2O)
- Bidentate ligands: Two donor atoms (e.g., ethylenediamine)
- Polydentate ligands: More than two donor atoms (e.g., EDTA)
12. How to find the type of ligand for JEE and NEET exams?
To find the ligand type for JEE/NEET:
- Look at the number of donor atoms present
- Identify if it forms rings (chelating), or can attach through different atoms (ambidentate)
- Refer to standard tables for common ligands
- Practice with previous years' questions to master identification
