NEET · Chemistry
Own official Unit 3: ionic/covalent bonding, energetic and polarity ideas at required depth, Fajan considerations, VSEPR geometry, valence-bond/hybridisation, resonance, molecular orbital theory, metallic bonding and hydrogen bonding.
In short
Chemical bonding questions are solved by selecting the right model. Use ionic/electrostatic and lattice ideas for ionic solids, Lewis/VSEPR/hybridisation for local geometry, resonance when one Lewis structure is insufficient, and molecular orbital theory when bond order or magnetism requires a delocalised orbital picture.
Ionic bonding is dominated by electrostatic attraction between oppositely charged ions, while covalent bonding shares electron density between atoms. Real bonds can show mixed character. Polarising power and polarisability help explain why some nominally ionic combinations show increased covalent character.
VSEPR starts from electron-domain repulsions around the central atom. Electron-domain geometry and observed molecular shape are not always identical because lone pairs occupy domains but are not named as bonded atoms in the molecular shape.
Useful idealised baselines:
Lone pairs and multiple-bond domain effects can modify bond angles, so ideal angles are reference values, not universal exact results.
When equivalent or important Lewis contributors differ only in electron placement, the actual electronic structure is represented by a resonance hybrid rather than rapid switching between discrete structures. Atom positions remain fixed between valid resonance contributors.
MOT combines atomic orbitals into bonding and antibonding molecular orbitals. Bond order is 1/2(N_b - N_a). Higher positive bond order generally indicates stronger bonding within a comparable series. Unpaired electrons in occupied molecular orbitals imply paramagnetism.
Hydrogen bonding requires the appropriate strongly polar X-H donor and an electron-rich acceptor environment, most commonly involving N, O or F in standard NEET chemistry. Intermolecular and intramolecular hydrogen bonding can affect boiling point, solubility and molecular conformation differently.
Dipole moment mu = q r vector concept: Charge separation; molecular dipoles combine vectorially. Calling a molecule polar because each bond is polar without considering geometry.
Dipole moment mu = q r vector concept
Use when — Calling a molecule polar because each bond is polar without considering geometry.
VSEPR domain count: Count sigma-bond directions and lone-pair domains; multiple bond is one direction domain. Equating electron geometry with molecular shape.
VSEPR domain count
Use when — Equating electron geometry with molecular shape.
bond order = (N_b-N_a)/2: MOT electron occupancy known. Counting atomic electrons without filling the correct MO sequence.
bond order = (N_b-N_a)/2
Use when — Counting atomic electrons without filling the correct MO sequence.
sp -> linear 180 deg: Ideal two-domain reference. Applying to a species with different electron-domain count.
sp -> linear 180 deg
Use when — Applying to a species with different electron-domain count.
sp2 -> trigonal planar 120 deg: Ideal three-domain reference. Ignoring lone pairs.
sp2 -> trigonal planar 120 deg
Use when — Ignoring lone pairs.
sp3 -> tetrahedral 109.5 deg: Ideal four-domain electron geometry. Calling NH3 tetrahedral molecular shape.
sp3 -> tetrahedral 109.5 deg
Use when — Calling NH3 tetrahedral molecular shape.
Original NEET-style item: In the simple molecular-orbital description of O2, the occupied antibonding pi* orbitals contain two unpaired electrons. If the total bonding-electron count is 10 and antibonding count is 6, find bond order and magnetic behaviour.
Reasoning: bond order = (10-6)/2 = 2. The two unpaired electrons make O2 paramagnetic. The magnetic conclusion cannot be obtained correctly from a simple Lewis structure alone, which is why MOT is the right model.
Cannot distinguish electron geometry from molecular shape
Knowledge gapWhy it happens
Preparation Intelligence classification: Knowledge Gap.
How it is corrected
Count all domains, then hide lone-pair positions for shape name.
Forgets ideal VSEPR baselines
Recall gapWhy it happens
Preparation Intelligence classification: Recall Gap.
How it is corrected
Retrieve domain count with shape/angle condition.
Adds bond dipoles arithmetically instead of vectorially
Execution errorWhy it happens
Preparation Intelligence classification: Execution Error.
How it is corrected
Use molecular geometry before deciding polarity.
Uses hybridisation to answer O2 magnetism
Decision / selection errorWhy it happens
Preparation Intelligence classification: Decision / Selection Error.
How it is corrected
Select MOT for bond order/magnetism.
MO ordering or a special species is uncertain
Needs reviewWhy it happens
Preparation Intelligence classification: Needs Review.
How it is corrected
Use NCERT/SME source rather than extrapolating.
FAQ
Straight answers about how Rank Sarthi fits into serious exam preparation.
Not always. Lone pairs contribute to electron-domain geometry but are omitted from the molecular-shape name.
bond order = (bonding electrons - antibonding electrons)/2.
Bond dipoles are vectors; a symmetric molecular geometry can cancel them.
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.
