NEET Chemistry Coordination Compounds 2027 — Werner Theory, CFT, Isomerism and 40 Practice MCQs

Last Updated: 11 May 2026

Coordination Compounds is among the highest-yield NEET 2027 chapters in Inorganic Chemistry — 3-4 questions worth 12-16 marks. NCERT Class 12 Ch. 9 has driven 18 NEET questions in the last 5 years, including 4 in NEET 2026.

Werner’s Coordination Theory (1893)

1. A metal exhibits two types of valencies — primary (ionisable) and secondary (non-ionisable).
2. Primary valencies are satisfied by negative ions; secondary valencies by ligands.
3. Every metal has a fixed coordination number (secondary valency).
4. Secondary valencies are directional → gives specific geometry.

Key Terminology

• Coordination Sphere: [M(L)n]; written inside square brackets.
• Ligand: Lewis base donating electron pair(s).
• Denticity: number of donor atoms — Monodentate (Cl-, NH3), Bidentate (en, ox), Polydentate (EDTA — hexadentate).
• Chelate: ring-forming polydentate ligand.
• Ambidentate: can bind through different atoms — SCN- (S or N), NO2- (N or O).

IUPAC Nomenclature Rules

1. Cation named first.
2. Within complex: ligands alphabetically (ignore Greek prefix).
3. Prefixes: di-, tri-, tetra- (mono/poly for complex names use bis-, tris-, tetrakis-).
4. Metal oxidation state in Roman numerals in parentheses.
5. For anionic complex, metal name ends in ‘-ate’ (e.g., ferrate, cuprate).

Isomerism in Coordination Compounds

Valence Bond Theory (VBT)

• Inner orbital complex: (n-1)d2sp3 — diamagnetic, low spin (strong field ligands).
• Outer orbital complex: sp3d2 — paramagnetic, high spin (weak field ligands).
• Ligand strength order (Spectrochemical series): I- < Br- < Cl- < F- < OH- < H2O < NH3 < en < CN- < CO.

Crystal Field Theory (CFT) Essentials

• Octahedral splitting: t2g (lower, 3 orbitals) and eg (higher, 2 orbitals). Δ_o = crystal field splitting energy.
• Tetrahedral splitting: e (lower, 2) and t2 (higher, 3); Δ_t ≈ 4/9 × Δ_o.
• CFSE (Crystal Field Stabilisation Energy): = (-0.4 × t2g electrons + 0.6 × eg electrons) × Δ_o.
• Colour: arises from d-d transitions; observed colour is complementary to absorbed.

Important Complexes (NCERT Examples)

• [Fe(CN)6]4-: d2sp3, diamagnetic, hexacyanoferrate(II), used in K4[Fe(CN)6].
• [Ni(CO)4]: sp3, tetrahedral, diamagnetic, Mond’s process.
• [Cu(NH3)4]2+: dsp2, square planar, paramagnetic.
• cis-[PtCl2(NH3)2]: anti-cancer drug (Cisplatin).
• EDTA-Ca2+: water hardness estimation.

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FAQ

Average questions from this chapter in NEET?

3-4 questions worth 12-16 marks.

Most-asked subtopic?

Isomerism (linkage + geometrical) — at least 1 question every year.

VBT or CFT — which is more tested?

Both. VBT (hybridisation + magnetic moment) and CFT (splitting + colour) are equally probable.

Practice Quiz

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