Coordination Compounds
Class 12 · Chemistry
4 ideas in Class 12 Chemistry, explained in plain words, with games and quizzes to practise.
Werner Theory and Key Terms
Part of: Werner Theory and Isomerism
Werner split valency into ionisable primary and directional secondary, the latter being today's coordination number. Ligands donate electron pairs: monodentate singly, bidentate doubly, ambidentate through either end, and chelates gripping like claws for extra stability.
Why it matters. Formulas, isomer counts and naming all start here. Mixing primary with secondary misreads every precipitation test.
Formulas
- Secondary valence = coordination number
- Free ions precipitate with silver nitrate
- Chelates beat monodentate analogues in stability
Key words
- Primary valence
- : Ionisable charge balanced by free ions.
- Coordination number
- : Donor atoms bound directly to the centre.
- Chelate
- : Ligand gripping metal through two or more atoms.
- Ambidentate ligand
- : Ligand binding through either of two atoms.
Try it in two minutes
- Count free ions for primary valence.
- Count donor atoms for coordination number.
- Sort ligands by denticity and bite.
Try at home. Predict AgCl precipitate moles for three cobalt ammine chlorides.
Nomenclature and Isomerism
Part of: Werner Theory and Isomerism
Names list ligands alphabetically before the metal with its oxidation state, adding -ate for anionic spheres. Same-formula complexes differ as ionisation, linkage, coordination or solvate isomers, or as cis-trans, fac-mer and mirror-image optical forms.
Why it matters. Catalogues, patents and exams all use exact names. Misordering ligands or missing chirality loses the compound's identity.
Formulas
- Ligands alphabetical, then metal with (OS)
- Anionic sphere adds -ate to metal
- Cis neighbours touch; trans sit opposite
Key words
- IUPAC name
- : Systematic name with ligands, metal and oxidation state.
- Ionisation isomerism
- : Swapping groups inside and outside brackets.
- Linkage isomerism
- : Ambidentate ligand binding through different atoms.
- Optical isomerism
- : Non-superimposable mirror forms rotating light.
Try it in two minutes
- Order ligands alphabetically with prefixes.
- Add metal oxidation state in roman numerals.
- Test what swaps: ions, donor atoms, positions or mirrors.
Try at home. Name three salts from their formulas without looking.
Valence Bond Theory and Magnetism
Part of: Bonding Theories and Applications
Valence bond theory pairs electrons under strong-field ligands into inner d2sp3 orbitals, leaving weak-field outer sp3d2 sets unpaired. Counting the survivors with root n(n+2) predicts magnetism, though the theory cannot explain colours or spectra quantitatively.
Why it matters. Magnetic data reveals electronic structure directly. Calling every complex low-spin, or trusting VBT for colours, misreads evidence.
Formulas
- Moment: mu = sqrt(n(n + 2)) BM
- Strong field pairs; weak field spreads
- Magnetism counts unpaired electrons
Key words
- Inner orbital complex
- : Low-spin complex using inner d orbitals.
- Outer orbital complex
- : High-spin complex using outer d orbitals.
- Strong-field ligand
- : Ligand causing electron pairing, like CN- and CO.
Try it in two minutes
- Rank the ligand as strong or weak field.
- Pair electrons for strong fields only.
- Count survivors and apply root n(n+2).
Try at home. Predict moments for [FeF6]3- versus [Fe(CN)6]3-.
Crystal Field Theory and Uses
Part of: Bonding Theories and Applications
Ligands split d orbitals into lower t2g and upper eg sets by gap delta, small for weak fields (high spin) and large for strong fields (low spin). Absorbing gap-sized light colours complexes, back-bonding steadies carbonyls, and chelates carry metals in bodies and industry.
Why it matters. Rubies, haemoglobin and catalysts all run on splitting. Reversing t2g with eg, or missing the series order, breaks every colour and spin answer.
Formulas
- Octahedral: t2g lower, eg upper
- Strong field gives low spin; weak gives high spin
- Colour from absorbed gap light
Key words
- Crystal-field splitting
- : t2g-eg gap created by ligands, called delta.
- Spectrochemical series
- : Ligand order from weak to strong field.
- Chelate therapy
- : Treating metal poisoning with claw ligands.
Try it in two minutes
- Order the ligand in the spectrochemical series.
- Compare delta with pairing energy for spin.
- Match absorbed light with the gap.
Try at home. Order five ligands from weak to strong field.
What your child will practise
- Crystal Field Theory and Uses: Desert Quest (Flip and Match)
- Crystal Field Theory and Uses: Ocean Quick Fire (Quick Fire)
- Nomenclature and Isomerism: Jungle Puzzle (Clue Puzzle)
- Valence Bond Theory and Magnetism: Candy Quick Fire (Quick Fire)
- Werner Theory and Key Terms: Desert Puzzle (Clue Puzzle)
- Quiz: Crystal Field Theory and Uses (8 questions)
- Quiz: Nomenclature and Isomerism (8 questions)
- Quiz: Valence Bond Theory and Magnetism (8 questions)
- Quiz: Werner Theory and Key Terms (8 questions)