Overview
This lecture covers the basics of coordination chemistry, focusing on coordination compounds, their structure, valencies, types of ligands, and related calculations important for exams like JEE. Key concepts include primary and secondary valency, coordination number, types of ligands, chelates, and effective atomic number calculations.
Introduction & Importance
- Coordination chemistry is essential for competitive exams like JEE and appears frequently in questions.
- Coordination compounds involve a central metal atom surrounded by ligands.
Werner’s Theory: Primary & Secondary Valency
- Coordination compounds have two types of valency: primary (oxidation state) and secondary (coordination number).
- Primary valency equals the oxidation number of the central metal.
- Secondary valency equals the number of ligands attached (coordination number).
Structure & Representation of Coordination Compounds
- Example: [Co(NH₃)₆]Cl₃, where Co is the central atom, NH₃ is the ligand, and Cl⁻ ions are outside.
- Primary valency is satisfied by ions outside the square brackets, secondary by ligands inside.
- The coordination number is determined by the number of ligand donor atoms attached to the metal.
Ligands: Types & Classification
- Ligands are molecules/ions donating electron pairs to the central metal.
- Classified as monodentate (one donor), bidentate (two donors), polydentate (multiple donors), and ambidentate (can bind through more than one atom but only one at a time).
- Chelates form when ligands bind through two or more donor atoms, creating a ring.
Calculating Oxidation State & Coordination Number
- Oxidation state: X + sum of ligand charges + charge outside bracket = 0.
- Coordination number: Count the number of donor atoms from all ligands.
Effective Atomic Number (EAN) Concept
- EAN = (Atomic number of metal) – (oxidation state) + (2 × coordination number).
- EAN often matches the atomic number of the nearest noble gas.
Double Salts vs. Complex Compounds
- Double salts dissociate completely in solution and give characteristic tests for all ions.
- Complex compounds retain their structure in solution; only the ions outside the brackets dissociate.
Electrical Conductivity
- The number of ions formed in solution determines the electrical conductivity.
- Higher ion count = higher conductivity.
Key Terms & Definitions
- Coordination Compound — Compound with a central metal atom/ion bonded to surrounding ligands.
- Primary Valency — Oxidation number of the central metal atom/ion.
- Secondary Valency — Number of ligand donor atoms attached to the metal (coordination number).
- Ligand — Ion/molecule donating an electron pair to the metal.
- Monodentate/Bidentate/Polydentate — Ligands donating one, two, or multiple pairs of electrons, respectively.
- Chelate — Complex where the ligand forms a ring structure with the metal.
- Effective Atomic Number (EAN) — Total electrons counted for the metal plus donated electrons from ligands.
Action Items / Next Steps
- Practice calculating oxidation states, coordination numbers, and EAN for given coordination compounds.
- Review NCERT examples and previous year exam questions on coordination chemistry.
- Revise concepts of ligand classification and structure drawing for complexes.
- Watch related crash course videos for further clarification if needed.