Coordination Compounds — Revision Notes
Punjab Board · Class 12 · Chemistry
Coordination Compounds revision notes for Punjab Board Class 12 Chemistry: 4 topics in quick points. Part of the Punjab Board Class 12 Chemistry syllabus.
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Key Topics to Revise
Werner's Theory of Coordination Compounds
- Alfred Werner (1866–1919) was a Swiss chemist who first systematically explained coordination compounds and won the Nobel Prize in Chemistry in 1913.
- Werner proposed two types of valences for metal ions: PRIMARY VALENCE (ionisable, satisfied by negative ions) and SECONDARY VALENCE (non-ionisable, satisfied by neutral molecules or negative ions).
- Primary valence = oxidation state of the metal; Secondary valence = coordination number of the metal.
Key Definitions and Terminology
- COORDINATION ENTITY: The central metal atom/ion plus all its ligands, enclosed in square brackets.
- CENTRAL ATOM/ION: The metal atom or ion at the centre of the coordination entity; acts as a Lewis acid (electron pair acceptor). Examples: Ni²⁺ in [NiCl₂(H₂O)₄], Co³⁺ in [CoCl(NH₃)₅]²⁺, Fe³⁺ in [Fe(CN
- LIGAND: Ions or molecules bonded to the central atom; act as Lewis bases (electron pair donors). Can be simple ions (Cl⁻), small molecules (H₂O, NH₃), or large molecules (EDTA).
Nomenclature of Coordination Compounds
- IUPAC rules are used for systematic naming. The cation is always named FIRST, then the anion.
- FORMULA WRITING ORDER: Central metal first, then ligands listed ALPHABETICALLY. Entire coordination entity enclosed in square brackets [ ].
- NAMING ORDER: Ligands are named ALPHABETICALLY before the central metal name. (Reverse of formula writing for ligand order.)
Isomerism in Coordination Compounds
- ISOMERS: Compounds with same molecular formula but different arrangement of atoms, resulting in different properties.
- TWO MAIN TYPES: (A) Stereoisomerism — same bonds, different spatial arrangement; (B) Structural isomerism — different bonds.
- GEOMETRIC ISOMERISM (Stereoisomerism): Arises in heteroleptic complexes due to different spatial arrangements of ligands.
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