Subtopics - Chemical Bonding (NEET)
Nine interconnected topic blocks: Lewis theory and octet rule, ionic/covalent/coordinate/metallic bond types, dipole moment as a measure of bond polarity, physical properties comparison of ionic and covalent compounds, Fajan's rule for covalent character prediction, five types of hybridisation with geometry, VSEPR theory for molecular shape prediction, Molecular Orbital Theory with bond order and magnetism, and hydrogen bonding with intermolecular and intramolecular types.
1) Lewis Theory
Explains covalent bonding through shared electron pairs. The octet rule states that atoms form bonds until surrounded by eight electrons (hydrogen needs only two). Lewis dot structures use dashes for bonds and dots for lone pairs. A systematic method determines bonding and non-bonding electrons from total valence electron count.
2) Types of Chemical Bonds
Covers four fundamental bond types: ionic bond (electron transfer between electropositive and electronegative atoms), covalent bond (electron sharing with sigma and pi overlap), coordinate bond (both shared electrons from one donor atom), and metallic bond (delocalised electron sea model). Each bond type is linked to element electronegativity character.
3) Dipole Moment
Measures the degree of polarity in a molecule. Dipole moment mu = charge (e) times distance (d), expressed in Debye (D) where 1D = 10 to the minus 18 esu-cm. It is a vector quantity and the net dipole moment is the vector sum of individual bond moments. Zero net dipole indicates molecular symmetry.
4) Physical Properties of Ionic and Covalent Compounds
Compares the physical behaviour of ionic and covalent compounds across three properties: melting point (ionic compounds have high MP due to strong lattice forces, covalent compounds have low MP due to weak van der Waals forces), conductivity (ionic compounds conduct when molten or dissolved, covalent compounds do not), and solubility (like dissolves like principle with dielectric constant).
5) Fajan's Rule
Explains why ionic bonds develop partial covalent character. When a cation polarises the electron cloud of an anion, the bond gains covalent character. Four factors favour covalent character: small cation (high polarising power), large anion (high polarisability), high charge on either ion, and cation with pseudo noble gas configuration (18 electrons in outermost shell).
6) Hybridisation
The intermixing of atomic orbitals of the same atom having similar energies, followed by redistribution to form new hybrid orbitals of identical energy and shape. Five types: sp3 (tetrahedral, 109.5 degrees), sp2 (trigonal planar, 120 degrees), sp (linear, 180 degrees), sp3d (trigonal bipyramidal), sp3d2 (octahedral). The number of hybrid orbitals equals the number of atomic orbitals mixed.
7) VSEPR Theory
Predicts molecular geometry from electron pair repulsions in the valence shell. Lone pair repulsion is stronger than bond pair repulsion (lp-lp > lp-bp > bp-bp), causing bond angle reduction from ideal values. The N/2 shortcut determines hybridisation and the number of bonded atoms versus lone pairs fixes the molecular shape from a comprehensive chart covering linear through pentagonal bipyramidal geometries.
8) Molecular Orbital Theory
Treats electrons as waves that undergo constructive interference (bonding MO, lower energy) and destructive interference (anti-bonding MO, higher energy, marked with asterisk). Bond order = half the difference between bonding and anti-bonding electrons. Two energy level sequences exist: one for molecules up to N2 (pi before sigma-2p) and one for O2 onwards (sigma-2p before pi). Unpaired electrons in the MO configuration indicate paramagnetism.
9) Hydrogen Bonding
A weak attachment (2 to 10 kcal/mol) formed when hydrogen bonded to a strongly electronegative atom (F, O, or N) interacts with another electronegative atom. Requires high electronegativity and small size of the electronegative element. Strength order: F-H-F > O-H-O > N-H-N. Two types: intermolecular (between molecules, raises boiling point) and intramolecular (within same molecule, causes chelation). Critical for biological structures like protein alpha-helices.
Chemical Bonding Download Notes & Weightage Plan
For each topic in the Chemical Bonding chapter below, you get (2) the exact resources to download and how to use them, and (3) a simple importance & time plan so NEET students know what to do first and what to revise last.
Foundation for understanding covalent bonding: shared electron pairs, octet rule, Lewis dot structures, and formal charge calculation.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Formal charge calculation and knowing when octet rule is violated. Elements in Period 3 and beyond can expand their octet using d-orbitals.
- High-risk Area: Forgetting to adjust total valence electrons for ionic charge: add electrons for negative charge, subtract for positive charge. Missing this step gives wrong Lewis structure.
- Best Practice Style: Always count total valence electrons first, then apply the five-step method. Check formal charges on every atom to validate the structure.
Four fundamental bond types: ionic (electron transfer), covalent (sigma and pi overlap), coordinate (donor-acceptor), and metallic (delocalised electrons). Foundation for understanding molecular properties.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Counting sigma and pi bonds in a molecule: every single bond is one sigma, every double bond is one sigma plus one pi, every triple bond is one sigma plus two pi. NEET asks total sigma and pi bonds in molecules like CH3-CH=CH-C(triple bond)CH.
- High-risk Area: Forgetting that a coordinate bond, once formed, is identical to a covalent bond. All four N-H bonds in NH4-plus are equivalent despite one originating as a coordinate bond.
- Best Practice Style: For sigma/pi counting: draw the structural formula, count single bonds as sigma, double bonds as sigma+pi, triple bonds as sigma+2pi. Total up.
Quantifies bond polarity. mu = e times d in Debye units. Vector quantity requiring vector addition of individual bond moments to find net molecular dipole.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Zero dipole moment identification. If all bond dipoles cancel by symmetry, mu = 0. This links directly to molecular shape from VSEPR.
- High-risk Area: Assuming all tetrahedral molecules have zero dipole. Only symmetric tetrahedrals like CCl4 have zero mu. CHCl3 is tetrahedral but asymmetric, so mu is nonzero.
- Best Practice Style: First determine molecular geometry, then check if all surrounding atoms are identical. If yes, mu = 0. If any atom differs, mu is nonzero.
Physical Properties of Ionic and Covalent Compounds
Contrasts physical properties across three dimensions: melting point, electrical conductivity, and solubility, linking each to the nature of bonding and intermolecular forces.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: The key distinction: ionic compounds conduct when molten or dissolved (not in solid state). NEET distractors include solid ionic compounds conducting, which is false.
- High-risk Area: Stating that ionic compounds conduct in solid state. They do not; ions are locked in the lattice. Only when molten or dissolved do ions become mobile.
- Best Practice Style: Always specify the state when discussing conductivity of ionic compounds: molten state or aqueous solution allows conduction, solid state does not.
Predicts covalent character in ionic compounds based on ion polarisation. Four factors: cation size, anion size, ionic charge, and electronic configuration of cation.
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Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Ranking compounds by covalent character using Fajan's rule. Common NEET series: LiF < LiCl < LiBr < LiI (increasing covalent character with increasing anion size).
- High-risk Area: Confusing polarising power (cation property) with polarisability (anion property). Small cation has high polarising power. Large anion has high polarisability. Both increase covalent character.
- Best Practice Style: For any comparison: identify which Fajan factor differs between the two compounds, then apply that factor. If multiple factors differ, the dominant factor usually determines the answer.
Five hybridisation types: sp3, sp2, sp, sp3d, sp3d2 producing tetrahedral, trigonal planar, linear, trigonal bipyramidal, and octahedral geometries. The N/2 shortcut enables rapid determination.
1) Download Packs For This Topic (And How To Use Them)
Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: N/2 shortcut is the fastest way to identify hybridisation in NEET. Apply it to central atom: count valence electrons plus bonded atoms plus or minus charge, divide by 2, match to table.
- High-risk Area: Forgetting to include the ionic charge when using the N/2 shortcut. For NH4-plus: N = 5 + 4 minus 1 = 8, N/2 = 4, sp3 (correct). Omitting the charge gives N/2 = 4.5 which is meaningless.
- Best Practice Style: For every hybridisation question: (1) identify central atom, (2) count N using shortcut, (3) divide by 2, (4) match to hybridisation table, (5) subtract lone pairs for molecular shape.
Predicts molecular geometry based on electron pair repulsions. Lone pair repulsion exceeds bond pair repulsion. Combined with hybridisation to give exact molecular shapes and bond angles for any molecule or ion.
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Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Shape names for molecules with lone pairs: NH3 is trigonal pyramidal (NOT tetrahedral), H2O is bent (NOT tetrahedral), SF4 is seesaw (NOT tetrahedral), XeF4 is square planar (NOT octahedral). Name the shape from atom positions, not from total electron pair geometry.
- High-risk Area: Naming the electron pair geometry instead of the molecular geometry. VSEPR names molecular shapes from atom positions only. NH3 has tetrahedral ELECTRON geometry but trigonal pyramidal MOLECULAR geometry.
- Best Practice Style: For every molecule: (1) find total electron pairs from N/2, (2) determine lone pairs = total pairs minus bonded atoms, (3) look up molecular shape from VSEPR chart. Answer with the molecular geometry name, not the electron pair arrangement.
Models bonding through constructive (bonding MO) and destructive (antibonding MO) interference of atomic orbital waves. Bond order, magnetic character, and molecular stability are determined from the MO electronic configuration.
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2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Bond order of O2 = 2 with 2 unpaired electrons (paramagnetic). Bond order of N2 = 3, diamagnetic. These two molecules are tested repeatedly. Also know: if bond order = 0, molecule does not exist (He2, Ne2).
- High-risk Area: Using the wrong MO energy order. For molecules up to N2, pi-2p orbitals fill BEFORE sigma-2px. For O2 onwards, sigma-2px fills BEFORE pi-2p. Applying the wrong order gives wrong bond order and wrong magnetic prediction.
- Best Practice Style: First check: is the molecule N2 or lighter? Use order 1 (pi before sigma). Is it O2 or heavier? Use order 2 (sigma before pi). Then fill electrons following aufbau principle and Hund's rule.
Weak electrostatic attraction between H bonded to F, O, or N and another electronegative atom. Two types: intermolecular (raises BP, causes association) and intramolecular (chelation, lowers BP relative to intermolecular variant). Essential for biological structure stability.
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Don't download everything and forget it. Use these like a small "attack kit": read → highlight → test → revise the same sheet again.
2) Importance, Weightage & Time Allocation (Practical)
Use this to avoid over-studying. This topic is usually low effort, quick return if your recall is clean.
- Scoring Focus: Boiling point ordering based on hydrogen bond strength and type. Ortho-nitrophenol vs para-nitrophenol comparison is a classic: ortho has intramolecular H-bond (lower BP, volatile in steam), para has intermolecular H-bond (higher BP, non-volatile in steam).
- High-risk Area: Assuming Cl forms hydrogen bonds because its EN equals N (3.0). Cl does NOT form effective H-bonds due to its larger size. Only F, O, and N form hydrogen bonds in the periodic table.
- Best Practice Style: For every H-bonding question: (1) check if H is bonded to F, O, or N, (2) check if the interacting atom is also F, O, or N, (3) determine type (inter or intra), (4) predict property accordingly.
Chemical Bonding Chapter NEET Traps & Common Mistakes (Topic-Wise)
Each subtopic below is of the Chemical Bonding chapter and shows what NEET students usually do wrong in NEET examination, a short example of the mistake, and how NEET frames the question to trick you with close options are given below.
Mistake Snapshot (What Students Do Wrong)
- Using the wrong MO energy level order for O2: Two MO energy orders exist. For molecules up to N2, pi-2p fills before sigma-2px. For O2 and beyond, sigma-2px fills before pi-2p. Using the wrong order places electrons in incorrect orbitals, giving wrong bond order and magnetic character.
- Predicting O2 as diamagnetic based on Lewis structure: The Lewis structure of O2 shows a double bond with all paired electrons, which wrongly suggests diamagnetic character. MOT correctly places 2 electrons in degenerate pi-star orbitals with parallel spins (Hund's rule), predicting paramagnetic behaviour confirmed experimentally.
O2 has 16 electrons. Using the correct MO order for O2: KK sigma-2s2 sigma-star-2s2 sigma-2px2 pi-2py2 pi-2pz2 pi-star-2py1 pi-star-2pz1. Bond order = (10 minus 6)/2 = 2. Two unpaired electrons in pi-star orbitals make O2 paramagnetic. If you mistakenly use the N2 order (pi before sigma), you get the same bond order but might misplace electrons and miss the unpaired electron count.
How NEET Frames The Trap
NEET asks the magnetic nature of O2 or bond order of a diatomic molecule. Students who use one universal MO order get wrong results for molecules near the N2/O2 boundary.
Q. Which diatomic species is paramagnetic with bond order 2?
A. N2 B. O2 C. F2 D. C2
Trick: N2 has bond order 3, diamagnetic. O2 has bond order 2, paramagnetic (2 unpaired electrons in pi-star orbitals). F2 has bond order 1, diamagnetic. C2 has bond order 2 but is diamagnetic (no unpaired electrons). Students confuse C2 and O2 because both have bond order 2, but only O2 is paramagnetic.
Mistake Snapshot (What Students Do Wrong)
- Naming electron pair geometry instead of molecular shape: VSEPR names molecular shapes from atom positions only, excluding lone pairs. NH3 is trigonal pyramidal (not tetrahedral). H2O is bent (not tetrahedral). Students who report the electron pair arrangement instead of the molecular geometry lose the mark.
- Forgetting to include ionic charge in the N/2 hybridisation shortcut: For ions like NH4-plus, the charge must be subtracted from N: N = 5 + 4 minus 1 = 8, N/2 = 4 (sp3 tetrahedral). For SO4-2-minus, add 2 for the negative charge. Omitting the charge gives wrong N/2 and wrong hybridisation.
What is the shape of SF4? S has 6 valence electrons, bonds to 4 F atoms. N = 6 + 4 = 10, N/2 = 5, so sp3d hybridisation with 5 electron pairs. 5 pairs minus 4 bonded = 1 lone pair. Shape is seesaw (not trigonal bipyramidal). Naming it trigonal bipyramidal gives the electron pair geometry, not the molecular shape.
How NEET Frames The Trap
NEET asks for the shape of molecules with lone pairs on the central atom. The electron pair arrangement and the molecular shape have different names. Distractors use the electron pair geometry name.
Q. The shape of XeF4 molecule is
A. Tetrahedral B. Octahedral C. Square planar D. Square pyramidal
Trick: Xe has 8 valence electrons, bonds to 4 F atoms. N = 8 + 4 = 12, N/2 = 6, sp3d2 hybridisation. 6 pairs minus 4 bonded = 2 lone pairs. Octahedral electron geometry with 2 lone pairs gives square planar molecular shape. Option B (octahedral) is the electron pair geometry, not the molecular shape. Option D (square pyramidal) has only 1 lone pair.
Mistake Snapshot (What Students Do Wrong)
- Assuming ideal bond angles when lone pairs are present: Lone pairs occupy more space than bond pairs, compressing bond angles below the ideal value. sp3 ideal angle is 109.5 degrees, but NH3 is 107 degrees (1 lone pair) and H2O is 104.5 degrees (2 lone pairs). NEET distractors offer 109.5 for both.
- Not recognising that multiple bonds cause greater repulsion than single bonds: A double bond has greater electron density than a single bond and repels more strongly. In molecules like SO2 (two S=O double bonds plus one lone pair), bond angle is close to 120 degrees but not exactly, due to double bond repulsion exceeding single bond repulsion.
Bond angle in NH3 vs CH4 vs H2O. CH4 has 4 bond pairs, ideal tetrahedral angle 109.5 degrees. NH3 has 3 bond pairs and 1 lone pair; lone pair compresses bond angle to 107 degrees. H2O has 2 bond pairs and 2 lone pairs; two lone pairs compress angle further to 104.5 degrees. All three are sp3 hybridised but bond angles differ.
How NEET Frames The Trap
NEET asks to arrange NH3, H2O, CH4 in order of increasing or decreasing bond angle. Students who give the same angle (109.5) for all three because they are all sp3 lose the mark.
Q. Arrange in decreasing order of bond angle: CH4, NH3, H2O
A. CH4 > NH3 > H2O B. H2O > NH3 > CH4 C. NH3 > CH4 > H2O D. All have equal bond angles
Trick: All are sp3. CH4 has 0 lone pairs (109.5 degrees). NH3 has 1 lone pair (107 degrees). H2O has 2 lone pairs (104.5 degrees). Decreasing order: CH4 > NH3 > H2O. Option D (equal angles) ignores lone pair compression. Option B reverses the order.
Mistake Snapshot (What Students Do Wrong)
- Confusing polarising power with polarisability: Polarising power is a cation property (ability to distort anion electron cloud). Polarisability is an anion property (susceptibility to distortion). Mixing them up leads to wrong ordering. Small cation = high polarising power. Large anion = high polarisability.
- Ignoring electronic configuration effect in Fajan's rule: Cations with pseudo noble gas configuration (18 electrons, e.g., Cu-plus, Ag-plus) are more polarising than noble gas configuration cations (8 electrons, e.g., Na-plus, K-plus) of the same size and charge. Cu-plus (0.96 A) and Na-plus (0.95 A) have nearly identical radii and same charge, but CuCl is more covalent than NaCl.
Order LiCl, NaCl, KCl by covalent character. All have Cl-minus as anion (same polarisability). Cation size: Li-plus < Na-plus < K-plus. Smaller cation = higher polarising power = more covalent character. Order: LiCl > NaCl > KCl. Students who think larger cation polarises more get the reverse order.
How NEET Frames The Trap
NEET gives a series of compounds and asks to arrange by covalent or ionic character. Distractors reverse the effect of cation or anion size.
Q. Among NaCl, MgCl2, and AlCl3, which has the most covalent character?
A. NaCl B. MgCl2 C. AlCl3 D. All are equally ionic
Trick: Cation charge increases: Na-plus (1+), Mg-2-plus (2+), Al-3-plus (3+). Higher charge plus smaller cation radius gives greater polarising power. AlCl3 has the highest covalent character. NaCl has the least. Students who focus only on size and forget charge effect may pick MgCl2.
Mistake Snapshot (What Students Do Wrong)
- Assuming Cl forms hydrogen bonds because it has the same electronegativity as N: Both N and Cl have electronegativity 3.0 on the Pauling scale. However, hydrogen bond formation requires BOTH high electronegativity AND small atomic size. Cl is much larger than N, so the charge concentration around Cl is insufficient to form effective hydrogen bonds. Only F, O, and N form hydrogen bonds.
- Confusing intermolecular and intramolecular hydrogen bonding effects on boiling point: Intermolecular hydrogen bonding raises boiling point by causing molecular association. Intramolecular hydrogen bonding (chelation) forms a closed ring within the same molecule and PREVENTS intermolecular association, actually LOWERING boiling point. Ortho-nitrophenol (intramolecular H-bond) has a lower boiling point than para-nitrophenol (intermolecular H-bond).
Compare boiling points of o-nitrophenol and p-nitrophenol. In o-nitrophenol, the OH group forms an intramolecular hydrogen bond with the adjacent NO2 group (chelation). This internal bond prevents intermolecular hydrogen bonding. p-nitrophenol has no intramolecular H-bond, so it forms strong intermolecular H-bonds, raising its BP above the ortho isomer. Students who assume both isomers have similar BP miss this distinction.
How NEET Frames The Trap
NEET asks which isomer has a higher boiling point or which is steam-volatile. Students who do not distinguish between inter and intramolecular hydrogen bonding answer incorrectly.
Q. Which compound is steam-volatile: o-nitrophenol or p-nitrophenol?
A. o-nitrophenol B. p-nitrophenol C. Both are steam-volatile D. Neither is steam-volatile
Trick: o-Nitrophenol forms intramolecular hydrogen bonds (chelation), preventing intermolecular association. It behaves as a discrete molecule with low effective molecular mass. o-Nitrophenol is steam-volatile. p-Nitrophenol forms intermolecular H-bonds, creating molecular association and higher effective BP, making it non-volatile in steam.