Study Notes on Coordination Compounds for CBSE Class 12 Exam

Coordination Compounds - Exam Points

Introduction

  • Key concepts for CBSE Class 12 exam preparation regarding coordination compounds are presented.

Werner’s Theory

  • Coordination Sphere:

    • Definition: The part of a coordination compound that includes the central metal ion and the ligands directly bonded to it.

  • Complex Ion and Counter Ions Concept:

    • Complex Ion: A structure formed from a metal ion surrounded by ligands.

    • Counter Ions: Ions present outside the coordination sphere that balance the charge of the complex ion.

  • Geometrical Arrangement:

    • The spatial arrangement of ligands around the central metal ion is critical in determining the properties of coordination compounds.

    • Can dictate the reactivity and stability of the compound.

  • Secondary Valences Arrangement:

    • This refers to the fixed arrangement of ligands around a metal ion.

    • The geometry of the complex depends on the secondary valence.

    • Example: Tetrahedral, octahedral, square planar arrangements.

  • Secondary Valence (Coordination Number):

    • Definition: The number of ligand donor atoms that are bonded to the central metal ion.

    • It is fixed; typically determined by the metal's ability to accommodate ligands.

  • Non-Ionisable:

    • Important aspect of secondary valence indicating that the coordination sphere does not dissociate in solution.

  • Primary Valence:

    • Defined as the oxidation state of the metal ion in the coordination compound, and it is ionisable.

    • Determines the charge on the metal ion.

Key Definitions

  • Coordination Number:

    • Definition: The total number of σ-bonds formed between the central atom/ion and the ligands.

    • Only σ-bonds are counted when determining coordination number.

  • Chelate and Chelation:

    • Chelate: A complex formed when a ligand binds to a central metal ion through multiple bonds from a single ligand.

    • Chelation: The process by which a chelate forms, typically involving multidentate ligands.

Types of Ligands

  • Ligands: Molecules or ions that donate electron pairs to form a coordination bond with a central metal atom. They can be classified as:

    • Unidentate Ligands:

    • Definition: Ligands that can bind to a metal atom at one site only (e.g., Cl^-).

    • Didentate Ligands:

    • Definition: Ligands that can attach to the metal at two sites (e.g., ethylenediamine).

    • Polydentate Ligands:

    • Definition: Ligands that can attach at multiple sites, offering several donor atoms to bind with the metal (e.g., EDTA).

    • Ambidentate Ligands:

    • Definition: Ligands that can coordinate through two different donor atoms but can only bind at one site at a time (e.g., NO2^- can bind through N or O).