Class 12 Chemistry Chapter 9 – Coordination Compounds Notes (With Important Diagrams)

🧪 Chapter 9: Coordination Compounds – Class 12 Chemistry Notes

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🔍 Introduction

Coordination compounds are chemical compounds composed of a central metal atom/ion bonded to surrounding ligands through coordinate bonds. These compounds play a crucial role in biological systems, industrial catalysis, and analytical chemistry.

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📌 Important Terms and Definitions

Coordination Entity: Central metal atom/ion bonded to a fixed number of ligands.

Ligands: Ions or molecules that donate a pair of electrons to the metal.

Monodentate: Donates one pair (e.g., Cl⁻, NH₃).

Bidentate: Donates two pairs (e.g., ethylenediamine).

Polydentate: Donates more than two pairs (e.g., EDTA⁴⁻).

Coordination Number: Number of ligand donor atoms attached to central metal.

Chelate Complex: Complex formed by polydentate ligands.

Coordination Sphere: Part of complex enclosed in square brackets.

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🧲 Types of Ligands

Type Examples

Monodentate Cl⁻, CN⁻, NH₃

Bidentate C₂O₄²⁻ (oxalate), en

Polydentate EDTA⁴⁻

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🧬 Nomenclature Rules

1. Name ligands first (in alphabetical order), then central metal.

2. Anionic ligands end in -o (e.g., chloro, cyano).

3. Neutral ligands: aqua (H₂O), ammine (NH₃), carbonyl (CO).

4. For anionic complexes, metal ends with "-ate".

Example:

Cl₃ → Hexaamminecobalt(III) chloride

Nomenclature rules is very important and 

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🔁 Isomerism in Coordination Compounds

1. Structural Isomerism:

Ionisation Isomerism

Hydrate Isomerism

Linkage Isomerism

Coordination Isomerism

2. Stereoisomerism:

Geometrical Isomerism (cis/trans)

Optical Isomerism (non-superimposable mirror images)

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⚙️ Bonding in Coordination Compounds

Valence Bond Theory (VBT):

Central atom undergoes hybridisation.

Explains geometry:

sp³d² → Octahedral

d²sp³ → Inner orbital complex

sp³ → Tetrahedral

Limitations:

Cannot explain color or magnetic properties.

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🌈 Crystal Field Theory (CFT)

Considers metal-ligand interaction as purely electrostatic.

Ligand field causes d-orbital splitting:

Octahedral field: t₂g and e_g

Tetrahedral field: e and t₂

CFSE (Crystal Field Stabilization Energy): Helps predict stability and magnetic behavior.

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🧪 Stability of Coordination Compounds

Factors affecting stability:

Nature of ligand

Charge on central metal ion

Chelation enhances stability

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🧪 Applications of Coordination Compounds

Extraction of metals (cyanide process for gold)

Medicines (cisplatin – anticancer drug)

Water softening (using EDTA)

Analytical chemistry (complexometric titration)

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📘 Important Formulas

Coordination Number: Count of donor atoms.

Oxidation State: Metal ion charge considering ligand charges.

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📊 Important Diagram Names

1. d-Orbital Splitting in Octahedral Field

2. d-Orbital Splitting in Tetrahedral Field

3. Structure of [Co(NH₃)₆]³⁺ Complex

4. Linkage Isomerism Example: [Co(NO₂)(NH₃)₅]Cl₂

5. Optical Isomers of [Co(en)₃]³⁺

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📚 Quick Practice Questions

1. Define coordination number and give two examples.

2. Explain geometrical isomerism with an example.

3. Write IUPAC name of Cl.

4. Distinguish between homoleptic and heteroleptic complexes.

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📌 Conclusion: Coordination compounds are essential for understanding various chemical and biological pr

ocesses. Their bonding, isomerism, and stability are crucial for real-world applications like catalysis, therapy, and qualitative analysis.

Nomenclature rules and crystal field theory is very important.

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Written by: Shahid – Study with Shahid

👉 Visit: Shahid Notes Blog