NEET · Chemistry
Own official Unit 12: Werner framework, ligands/coordination number/denticity/chelation, nomenclature, isomerism, VBT, basic CFT, colour/magnetism and source-verified importance/applications.
In short
Start every coordination-compound problem by separating the bracketed coordination entity from counter-ions. Determine the complex charge, solve the metal oxidation state from ligand charges, count donor atoms for coordination number, and only then apply nomenclature, isomerism, VBT or basic crystal-field reasoning.
A coordination entity contains a central metal atom/ion surrounded by ligands. A ligand donates one or more donor-atom lone pairs to the metal. Denticity counts donor atoms from one ligand that bind the same centre. Coordination number counts donor atoms directly attached to the metal, not simply the number of ligand molecules.
Identify the charge on the bracketed entity using any counter-ions. Let metal oxidation state be x, add ligand charges, and set the sum equal to the complex-ion charge.
Example: [Co(NH3)6]Cl3 contains a +3 complex ion; NH3 is neutral, so Co is +3 and coordination number is 6.
Source-controlled examples:
Anionic coordination entities use the appropriate metal-name form such as ferrate. Ligand spelling/order and Roman-numeral oxidation state should follow the current NCERT/IUPAC teaching convention.
Use original diagrams.
VBT provides a geometry/hybridisation bonding model at current depth. In octahedral CFT, t2g lies lower and eg higher. In tetrahedral CFT, e lies lower and t2 higher, with smaller splitting than a comparable octahedral field. Do not add advanced ligand-field derivations.
Magnetic behaviour depends on oxidation state, d count, geometry and field context. The basic spin-only relation may be used where appropriate after these are known.
Applications may include source-verified roles in qualitative analysis, extraction/metallurgy and biological systems. Avoid unsupported medical/industrial claims.
metal oxidation state + sum ligand charges = complex charge: Use bracketed entity charge. Including counter-ions inside bracket equation.
metal oxidation state + sum ligand charges = complex charge
Use when — Including counter-ions inside bracket equation.
coordination number = donor atoms bound to metal: Count denticity. Calling one bidentate ligand one coordination site.
coordination number = donor atoms bound to metal
Use when — Calling one bidentate ligand one coordination site.
mu=sqrt(n(n+2)) BM: Basic spin-only model after d count/field state. Counting n before oxidation state.
mu=sqrt(n(n+2)) BM
Use when — Counting n before oxidation state.
Octahedral: t2g lower, eg higher: Standard octahedral CFT. Reversing with tetrahedral.
Octahedral: t2g lower, eg higher
Use when — Reversing with tetrahedral.
Tetrahedral: e lower, t2 higher: Basic tetrahedral CFT. Assuming same splitting order/magnitude as octahedral.
Tetrahedral: e lower, t2 higher
Use when — Assuming same splitting order/magnitude as octahedral.
Original NEET-style item: For [Co(NH3)5Cl]Cl2, determine Co oxidation state and coordination number.
Reasoning: Two external Cl- counter-ions mean the bracketed complex is +2. NH3 is neutral and coordinated Cl is -1. x-1=+2, so Co is +3. Five N donor atoms plus one Cl donor atom give coordination number 6.
Cannot distinguish ligand count from coordination number
Knowledge gapWhy it happens
Preparation Intelligence classification: Knowledge Gap.
How it is corrected
Count donor atoms explicitly.
Forgets ligand naming/order
Recall gapWhy it happens
Preparation Intelligence classification: Recall Gap.
How it is corrected
Retrieve rule with one verified example.
Solves metal oxidation state using neutral formula instead of complex charge
Execution errorWhy it happens
Preparation Intelligence classification: Execution Error.
How it is corrected
Separate brackets and counter-ions first.
Chooses isomerism type before checking connectivity/donor atom/geometry
Decision / selection errorWhy it happens
Preparation Intelligence classification: Decision / Selection Error.
How it is corrected
Run isomerism grid.
Field/geometry assumption not given
Needs reviewWhy it happens
Preparation Intelligence classification: Needs Review.
How it is corrected
Do not infer magnetic state beyond supported context.
FAQ
Straight answers about how Rank Sarthi fits into serious exam preparation.
Count donor atoms directly attached to the central metal; a bidentate ligand contributes two.
Determine bracketed complex charge, add known ligand charges and solve for the metal.
t2g is lower and eg higher in the standard octahedral convention.
Official scope is taken from the NEET (UG) 2026 syllabus and official NTA documents; concept structure follows current NCERT contents. No performance, weightage or question-frequency data is asserted.
