CBSE Class 12 Chemistry

Introduction to Coordination Compounds

Coordination compounds (also called complex compounds) are chemical substances where a central metal atom or ion is bonded to a group of surrounding molecules or ions called ligands.

These compounds are important in both inorganic chemistry and biological systems. For example:

• Chlorophyll (in plants) contains magnesium.
• Haemoglobin (in blood) contains iron.
• Vitamin B12 contains cobalt.

Key Concepts:

• Central Atom/Ion: Usually a metal like Fe, Co, Ni.
• Ligands: Ions or molecules that donate electrons to the metal (e.g., NH₃, Cl⁻, CN⁻).
• Coordination Number: Number of ligand atoms directly bonded to the central atom.
• Coordination Sphere: The central atom and its attached ligands, shown in square brackets.
• Isomerism: Coordination compounds can show different types of isomerism like geometrical and optical.

Why It Matters:

Coordination compounds are used in:

• Medicines (e.g., anti-cancer drug cisplatin).
• Industrial catalysts.
• Water treatment (e.g., EDTA).
• Photography and dyeing.