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Class 11 ChemistryChapter Summaries

9 chapters · Quick revision in under 3 minutes per chapter · Updated 2025-26

Ch 1

Some Basic Concepts of Chemistry

This chapter lays the quantitative foundation of chemistry by introducing the mole concept, atomic and molecular masses, and stoichiometry. Students learn to calculate empirical and molecular formulae from percentage composition data. Laws of chemical combination — conservation of mass, definite proportions, multiple proportions, and Gay-Lussac's law — are thoroughly covered. Molar volume, Avogadro's number, and limiting reagent calculations form the core of this chapter.

Topics covered

Laws of chemical combination: Law of Conservation of Mass, Law of Definite Proportions, Law of Multiple ProportionsDalton's Atomic Theory and its postulatesAtomic mass, molecular mass, and formula massMole concept: 1 mol = 6.022 × 10²³ particles; molar mass in g/molEmpirical and molecular formula from % compositionStoichiometry and stoichiometric calculationsLimiting reagent and percentage yieldMolarity (M = n/V) and molality (m = n/w in kg)

Ch 2

Structure of Atom

This chapter traces the evolution of atomic models from Thomson's plum-pudding model through Rutherford's nuclear model to Bohr's model and the quantum mechanical model. Quantum numbers, the aufbau principle, Pauli exclusion principle, and Hund's rule govern electronic configurations. The dual nature of matter (de Broglie relation) and Heisenberg's uncertainty principle are key modern concepts. Students must also understand hydrogen spectrum line series (Lyman, Balmer, Paschen).

Topics covered

Thomson's, Rutherford's, and Bohr's atomic models — observations and limitationsBohr's equation: Eₙ = −13.6/n² eV; rₙ = 0.529n² Å (for H)Quantum numbers: n (principal), l (azimuthal), mₗ (magnetic), ms (spin)Aufbau principle, Pauli Exclusion Principle, Hund's Rule of Maximum Multiplicityde Broglie relation: λ = h/mvHeisenberg's Uncertainty Principle: Δx · Δp ≥ h/4πElectronic configuration — notation and orbital filling orderHydrogen spectrum: Lyman (UV), Balmer (visible), Paschen, Brackett, Pfund series

Ch 3

Classification of Elements and Periodicity in Properties

This chapter covers the historical development of periodic classification from Döbereiner's triads to Mendeleev's table to the modern long form of the periodic table. Students study periodic trends in atomic radius, ionic radius, ionisation enthalpy, electron gain enthalpy, and electronegativity. The concept of effective nuclear charge (Zeff) and shielding is central to explaining all periodic trends. Anomalous properties of second-period elements and diagonal relationships are important for board exams.

Topics covered

Mendeleev's periodic law vs Modern periodic lawStructure of the modern periodic table: periods, groups, s/p/d/f blocksAtomic radius: covalent radius and van der Waals radius; trend across period and down groupIonisation enthalpy (IE₁ and IE₂): trend and exceptions (Be vs B; N vs O)Electron gain enthalpy: trend and anomaly (Cl > F)Electronegativity: Pauling scale; trend across period and down groupEffective nuclear charge (Zeff) and shielding effectDiagonal relationships (Li–Mg, Be–Al, B–Si)

Ch 4

Chemical Bonding and Molecular Structure

This chapter explains why and how atoms combine to form molecules using the octet rule, ionic bonding, covalent bonding, and VSEPR theory. Valence Bond Theory (VBT) introduces orbital overlap and hybridisation (sp, sp², sp³, sp³d, sp³d²), while Molecular Orbital Theory (MOT) describes bonding in terms of BMOs and ABMOs. Resonance, formal charge, dipole moment, and the properties of ionic and covalent compounds are important exam topics.

Topics covered

Kössel–Lewis approach: octet rule, Lewis dot structures, formal chargeIonic bond: formation, lattice energy, Born–Haber cycle conceptCovalent bond: VBT — sigma (σ) and pi (π) bondsVSEPR theory: predicting geometry (linear, trigonal planar, tetrahedral, trigonal bipyramidal, octahedral)Hybridisation: sp (BeCl₂), sp² (BF₃), sp³ (CH₄/NH₃/H₂O), sp³d (PCl₅), sp³d² (SF₆)Resonance: O₃, CO₃²⁻, SO₂; resonance energyMOT: bonding order = (Nb − Na)/2; paramagnetic O₂, diamagnetic N₂Dipole moment; polarity of molecules; hydrogen bond (inter and intra)

Ch 5

Thermodynamics

This chapter applies the laws of thermodynamics to chemical reactions, defining internal energy, enthalpy, and entropy as state functions. The first law (ΔU = q + w) and Hess's law of constant heat summation are foundational. Standard enthalpies of formation, combustion, atomisation, bond dissociation, and solution/hydration are covered in depth. The second law introduces entropy and spontaneity; the Gibbs free energy equation (ΔG = ΔH − TΔS) determines whether a reaction is spontaneous.

Topics covered

System, surroundings, state functions; intensive vs extensive propertiesFirst Law of Thermodynamics: ΔU = q + w; work = −PΔV for expansionEnthalpy: H = U + PV; ΔH = ΔU + ΔngRTHess's Law of Constant Heat SummationStandard enthalpy of formation (ΔfH°), combustion (ΔcH°), atomisation, bond dissociationEntropy (S) — measure of disorder; second law: ΔS_universe > 0 for spontaneous processGibbs free energy: ΔG = ΔH − TΔS; spontaneity at ΔG < 0Relationship between ΔG° and equilibrium constant K: ΔG° = −RT ln K

Ch 6

Equilibrium

This chapter examines both chemical and ionic equilibrium. For chemical equilibrium, the law of mass action gives the equilibrium constant expression (Kc and Kp), and Le Chatelier's principle predicts how equilibrium shifts on changing concentration, pressure, or temperature. Ionic equilibrium covers Arrhenius, Brønsted–Lowry, and Lewis definitions of acids and bases, pH, the ionic product of water (Kw), Ka, Kb, and their relationship pKa + pKb = pKw, as well as buffer solutions and the Henderson–Hasselbalch equation.

Topics covered

Law of mass action: Kc = [products]/[reactants] (equilibrium expression)Relation between Kp and Kc: Kp = Kc(RT)^ΔngLe Chatelier's Principle — effect of concentration, pressure, and temperatureBrønsted–Lowry acid–base theory; conjugate acid–base pairsIonic product of water: Kw = [H⁺][OH⁻] = 1 × 10⁻¹⁴ at 25°CpH = −log[H⁺]; pKa + pKb = 14Buffer solutions: Henderson–Hasselbalch equation pH = pKa + log([A⁻]/[HA])Solubility product (Ksp) and the common ion effect

Ch 7

Redox Reactions

This chapter develops the concept of oxidation and reduction in terms of electron transfer and changes in oxidation number. Students learn to assign oxidation states systematically and to balance redox equations by both the oxidation number method and the ion-electron (half-reaction) method. The electrochemical series and the concept of reducing and oxidising agents, disproportionation reactions, and comproportionation are also covered.

Topics covered

Classical concept: oxidation (gain of O / loss of H) and reduction (loss of O / gain of H)Electronic concept: oxidation (loss of e⁻), reduction (gain of e⁻); oxidising and reducing agentsOxidation number rules: assignment in compounds and ionsBalancing redox equations — oxidation number methodBalancing redox equations — ion-electron (half-reaction) method in acidic/basic mediumDisproportionation reactions (same element oxidised and reduced)Electrochemical series and its applications (reactivity, displacement reactions)

Ch 8

Organic Chemistry – Some Basic Principles and Techniques

This chapter introduces the principles of organic chemistry: classification of organic compounds, IUPAC nomenclature, types of organic reactions, reaction intermediates (carbocations, carbanions, free radicals, carbenes), electronic effects (inductive, mesomeric/resonance, hyperconjugation), and methods of purification. Qualitative analysis — detection of C, H, N, S, and halogens (Lassaigne's test) — and quantitative analysis (Dumas, Kjeldahl methods) are also covered.

Topics covered

IUPAC nomenclature: rules for naming alkanes, alkenes, alkynes, and functional group compoundsHomolytic vs heterolytic fission; electrophiles and nucleophilesReaction intermediates: carbocations (stability: 3° > 2° > 1°), carbanions, free radicalsInductive effect (+I and −I) and its applicationsResonance/mesomeric effect (+M and −M) — delocalisation of electronsHyperconjugation (Baker–Nathan effect) — stabilisation of alkenes and carbocationsPurification methods: distillation, recrystallisation, sublimation, chromatographyLassaigne's test: detection of N, S, halogens; Kjeldahl's method for % nitrogen

Ch 9

Hydrocarbons

This chapter systematically covers the chemistry of alkanes, alkenes, alkynes, and aromatic hydrocarbons. Alkane reactions include free-radical halogenation (mechanism in steps); alkene reactions include electrophilic addition (Markovnikov's rule, anti-Markovnikov addition via HBr/peroxide), ozonolysis, and oxidation. Alkynes form acidic H due to sp hybridisation. Benzene's aromaticity (Hückel's 4n+2 rule), electrophilic aromatic substitution (EAS — halogenation, nitration, sulphonation, Friedel-Crafts), and conformations (Sawhorse and Newman) of alkanes are key topics.

Topics covered

Free-radical halogenation of alkanes: initiation, propagation, termination stepsElectrophilic addition to alkenes: mechanism; Markovnikov's ruleAnti-Markovnikov addition (peroxide/Kharasch effect) — HBr onlyOzonolysis of alkenes and alkynesAcidity of terminal alkynes (sp C–H); reactions with Na, NaNH₂Aromaticity: Hückel's rule (4n+2 π electrons); benzene structureElectrophilic Aromatic Substitution (EAS): nitration, halogenation, sulphonation, Friedel–Crafts alkylation/acylationConformations of ethane: staggered (Newman) and eclipsed forms

Frequently Asked Questions

Can I revise Class 11 Chemistry in one day using summaries?

Yes. Each chapter summary here takes under 3 minutes to read. With 9 chapters, you can cover all of Class 11 Chemistry in a focused 2–3 hour session. Use these summaries to identify gaps — then revisit only those chapters in detail.

Are chapter summaries enough for CBSE Class 11 Chemistry board exam?

Summaries are for revision, not first learning. Use them after you've already studied the chapter — they quickly confirm what you remember and flag what you don't. For first-time study, read the NCERT textbook and work through important questions chapter-by-chapter.

What is covered in Class 11 Chemistry chapter summaries?

Each summary here covers the main concepts of the chapter, key topics that CBSE tests, and important points for the board exam. Deleted topics (removed from the 2025-26 CBSE syllabus) are clearly marked so you don't waste time on content that won't be tested.

What is the fastest way to revise Class 11 Chemistry for CBSE boards?

Read the chapter summary, then immediately close it and try to recall the key topics listed — without looking. Anything you miss, mark for one more read. This active recall method is proven to be 3× more effective than re-reading the textbook, and takes a fraction of the time.

Complete Study Pack — Class 11 Chemistry

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