Introduction to NCERT Exemplar Solutions for Class 12 Chemistry Chapter 9: Coordination Compounds
Coordination compounds form an essential branch of inorganic Chemistry. They are complex molecules or ions in which a central metal atom is bonded to surrounding ions or neutral molecules, called ligands. These compounds are significant not only from a theoretical point of view but also due to their wide applications in industry, medicine, and analytical chemistry. Class 12 Chapter 9 introduces the structural, bonding, and functional aspects of coordination compounds. The NCERT Exemplar Solutions provide detailed explanations to challenging questions, ensuring that students develop a deep and clear understanding of the topic.
Introduction to Coordination Compounds
A coordination compound consists of a central metal atom or ion surrounded by ligands. Ligands may be negative ions, positive ions, or neutral molecules that donate an electron pair to the metal atom through a coordinate bond. Examples include [Cu(NH₃)₄]²⁺ and [Fe(CN)₆]³⁻.
Exemplar questions test a student’s ability to identify ligands, calculate coordination numbers, and write correct formulas and structures. This builds the foundation for understanding more advanced concepts.
Nomenclature of Coordination Compounds
Learning the rules of nomenclature is crucial for writing and interpreting formulas of coordination compounds. The International Union of Pure and Applied Chemistry (IUPAC) has specific rules:
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Ligands are named first in alphabetical order.
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The metal name is written next, followed by its oxidation state in Roman numerals.
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Anionic complexes end with the suffix “-ate.”
Exemplar solutions provide step-by-step practice in naming complex ions, ensuring that students avoid common mistakes in board and entrance exams.
Bonding in Coordination Compounds
The chapter introduces different theories that explain bonding in coordination compounds:
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Werner’s Coordination Theory – The earliest explanation, which distinguished between primary and secondary valencies.
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Valence Bond Theory (VBT) – Explains hybridization of metal orbitals and geometry of complexes. For example, [Co(NH₃)₆]³⁺ is an octahedral complex formed through d²sp³ hybridization.
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Crystal Field Theory (CFT) – Explains the splitting of d-orbitals in the presence of ligands, leading to different colors and magnetic properties.
Exemplar problems test students’ ability to apply these theories to determine magnetic behavior, predict hybridization, and explain electronic arrangements.
Isomerism in Coordination Compounds
Coordination compounds often exhibit isomerism, where two or more compounds have the same composition but different structures. Types include:
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Structural isomerism (linkage, ionization, coordination, hydrate isomerism)
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Stereoisomerism (geometrical and optical isomerism)
Exemplar solutions provide diagrams and reasoning to identify different types of isomers in given complexes. These questions strengthen spatial understanding and conceptual clarity.
Stability of Coordination Compounds
The stability of complexes depends on the nature of ligands and the charge on the metal ion. The chelate effect increases stability when multidentate ligands are involved, as seen in ethylenediamine complexes. Exemplar problems explain the role of stability constants and help students understand why certain complexes are more stable than others.
Applications of Coordination Compounds
Coordination chemistry has immense practical importance:
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Medicinal uses: Cisplatin is used in cancer therapy, while EDTA is used to treat heavy metal poisoning.
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Industrial uses: Complexes are used in electroplating, textile dyeing, and catalysis.
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Analytical chemistry: Complex formation is used in qualitative and quantitative analysis, such as detecting metal ions with colorimetric tests.
Exemplar problems often focus on these applications, ensuring that students can connect theory with real-world relevance.