NCERT Class 12 Chemistry Chemistry-I: Chapter 5 — Coordination Compounds
This chapter, "Coordination Compounds," introduces students to the fundamental concepts of coordination chemistry, a vital area in inorganic and bio-inorganic chemistry. It begins by defining coordination compounds as complexes formed by transition metals with anions or neutral molecules. The chapter details Werner's theory, explaining primary and secondary valences and introducing key terms like coordination entity, central atom/ion, ligand, coordination number, and coordination sphere. It also covers the rules for naming coordination compounds, different types of isomerism, and the nature of bonding through Valence Bond and Crystal Field theories. The importance and applications of coordination compounds in various fields, including biology (haemoglobin, chlorophyll), metallurgy, catalysis, and medicine, are highlighted, emphasizing their significance in modern science and industry.
Quick info
| Board | CBSE / NCERT |
|---|---|
| Class | Class 12 |
| Subject | Chemistry |
| Book | Chemistry-I |
| Chapter | Chapter 5 — Coordination Compounds |
| Language | English |
| PDF type | NCERT Textbook |
| Session | CBSE 2026 |
| Reading time | 4 minutes |
| Word count | 749 |
Learning outcomes
- Appreciate the postulates of Werner's theory of coordination compounds.
- Understand the definitions of key terms: coordination entity, central atom/ion, ligand, coordination number, coordination sphere, coordination polyhedron, oxidation number, homoleptic, and heteroleptic.
- Learn the rules for nomenclature of coordination compounds.
- Define different types of isomerism in coordination compounds.
- Understand the nature of bonding in coordination compounds using Valence Bond and Crystal Field theories.
- Appreciate the importance and applications of coordination compounds.
Vocabulary
| Word | Meaning |
|---|---|
| Coordination compounds | Compounds containing a central metal atom or ion bonded to a number of surrounding molecules or ions. |
| Ligand | An ion or molecule that binds to a central metal atom to form a coordination complex. |
| Coordination number | The number of ligand atoms directly bonded to the central metal atom. |
| Coordination sphere | The central metal atom/ion and the ligands bound to it, usually enclosed in square brackets. |
| Primary valence | Ionizable valency of a metal atom/ion in a coordination compound, usually satisfied by anions. |
| Secondary valence | Non-ionizable valency of a metal atom/ion, equal to the coordination number, satisfied by neutral molecules or anions. |
| Isomers | Compounds with the same molecular formula but different structural arrangements and properties. |
| Homoleptic | Coordination compounds in which all the ligands are identical. |
| Heteroleptic | Coordination compounds in which the ligands are of different types. |
| Coordination polyhedron | The spatial arrangement of ligands around the central metal atom. |
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Practice questions
- What is the difference between primary and secondary valence according to Werner's theory? Answer: Primary valence is ionizable and satisfied by negative ions, while secondary valence is non-ionizable and equal to the coordination number, satisfied by neutral molecules or negative ions.
- Define coordination number. Answer: Coordination number is the number of ligand atoms directly bonded to the central metal atom in a coordination compound.
- Give an example of a coordination compound found in nature. Answer: Haemoglobin (iron), chlorophyll (magnesium), and vitamin B12 (cobalt) are examples of coordination compounds found in nature.
- What are isomers in the context of coordination compounds? Answer: Isomers are compounds with the same molecular formula but different properties due to different spatial arrangements of ligands around the central metal atom.
Practice MCQs
Q1. Who was the first to formulate ideas about the structures of coordination compounds?
Explanation: Alfred Werner, a Swiss chemist, was the first to propose a theory explaining the structures of coordination compounds.
Q2. In Werner's theory, which valence is normally ionisable?
Explanation: Werner's theory states that primary valences are normally ionisable and are satisfied by negative ions.
Q3. The number of groups bound directly to the metal ion in Werner's theory is called:
Explanation: The number of groups bound directly to the metal ion is termed secondary valence, which is equal to the coordination number.
Q4. Which of the following is an example of a homoleptic coordination compound?
Explanation: [Co(NH3)6]3+ is a homoleptic compound because all the ligands are ammonia molecules. The others contain different types of ligands.
Q5. The species within the square bracket in a coordination compound formula are called:
Explanation: The species within the square bracket, consisting of the central metal atom/ion and ligands, are known as coordination entities or complexes.
Frequently asked questions
What are coordination compounds?
Coordination compounds are complex compounds where a central metal atom or ion is bonded to a number of anions or neutral molecules through coordinate covalent bonds.
What is the significance of Werner's theory?
Werner's theory was the first to explain the structure and bonding in coordination compounds, introducing concepts like primary and secondary valences and the coordination number.
What is the difference between a coordination entity and a counter ion?
The coordination entity is the central metal atom/ion along with its ligands, usually enclosed in square brackets. Counter ions are the ions outside the square brackets that balance the charge of the coordination entity.
Give examples of coordination compounds in biological systems.
Haemoglobin (iron), chlorophyll (magnesium), and vitamin B12 (cobalt) are important coordination compounds found in biological systems.
What are the main types of isomerism in coordination compounds?
The main types include structural isomerism (ionization, linkage, coordination, hydrate isomerism) and stereoisomerism (geometric and optical isomerism).
What is the role of ligands in coordination compounds?
Ligands are molecules or ions that donate electron pairs to the central metal atom/ion, forming coordinate covalent bonds and influencing the compound's properties.
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NCERT Class 12 Chemistry — Chemistry-I — Chapter 5 — Coordination Compounds. Verified by NCERT Help Editorial Team. Reviewed on 29 Jul 2026. Last updated 10 Aug 2026.