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Class 11th Chemistry NCERT Exemplar Solutions
1. Some Basic Concepts Of Chemistry
This foundational chapter introduces the language and quantitative tools of chemistry. It begins by classifying matter and defining its properties, establishing the importance of precision, accuracy, and the International System of Units (SI). The chapter explains the fundamental Laws of Chemical Combination, which govern chemical reactions, and introduces Dalton's Atomic Theory. The core of the chapter is the mole concept, a cornerstone of chemical calculations that relates mass to the number of particles (Avogadro's constant). It teaches how to calculate atomic mass, molecular mass, and molar mass, which are then applied to understand empirical and molecular formulae, stoichiometry, and calculations based on balanced chemical equations, including limiting reagents and concentrations of solutions (molarity, molality).
2. Structure Of Atom
This chapter unravels the internal structure of the atom, moving from classical to modern quantum mechanical models. It chronicles the discovery of subatomic particles and the development of atomic models, from Thomson's to Rutherford's nuclear model, and then to Bohr's model which explained the line spectrum of hydrogen. The chapter then introduces the dual nature of matter and radiation, including de Broglie's hypothesis and Heisenberg's uncertainty principle. This leads to the modern quantum mechanical model of the atom, which describes electrons in terms of atomic orbitals defined by a set of four quantum numbers (n, l, m, s). It explains the shapes of s, p, and d orbitals and the rules for filling electrons into these orbitals: the Aufbau principle, Pauli exclusion principle, and Hund's rule of maximum multiplicity.
3. Classification Of Elements And Periodicity In Properties
This chapter explains the systematic organization of elements in the Modern Periodic Table. It starts with a historical perspective, including Mendeleev’s contributions, and then details the modern periodic law based on atomic number. The chapter explains the arrangement of elements into s, p, d, and f blocks based on their electronic configurations. The main focus is on the periodicity of properties—the predictable trends observed across periods and down groups. Key properties discussed include atomic radius, ionic radius, ionisation enthalpy (energy to remove an electron), electron gain enthalpy (energy change on adding an electron), and electronegativity (tendency to attract shared electrons). Understanding these trends is crucial for predicting chemical behaviour.
4. Chemical Bonding And Molecular Structure
This chapter is central to chemistry, explaining how atoms are held together to form molecules. It details the formation of ionic bonds (by electron transfer) and covalent bonds (by electron sharing), using Lewis structures to represent them. The chapter introduces theories to predict the shape and geometry of molecules, including the Valence Shell Electron Pair Repulsion (VSEPR) theory. To explain the nature of covalent bonds more deeply, it covers the Valence Bond Theory (VBT), which introduces the concept of orbital overlap and hybridisation (sp, sp², sp³), and the Molecular Orbital Theory (MOT). It also discusses bond parameters like bond length and bond energy, and the importance of intermolecular forces like hydrogen bonding.
5. States Of Matter
This chapter explores the physical states of matter, with a primary focus on gases and liquids. It explains how the balance between intermolecular forces and thermal energy determines the state of a substance. The behavior of gases is described by the fundamental gas laws (Boyle’s, Charles’s, Avogadro's), which are combined to form the Ideal Gas Equation (PV = nRT). The chapter introduces Dalton’s Law of Partial Pressures and the Kinetic Molecular Theory of Gases to provide a microscopic explanation for macroscopic gas properties. It also discusses the deviation of real gases from ideal behavior. For liquids, key properties like vapour pressure, surface tension, and viscosity are explained.
6. Thermodynamics
This chapter deals with energy, heat, work, and the spontaneity of processes. It introduces key thermodynamic concepts like system, surroundings, and state functions. The First Law of Thermodynamics, the law of conservation of energy, is discussed in terms of internal energy (ΔU), heat (q), and work (w). The concept of enthalpy (ΔH) is introduced to study heat changes at constant pressure, including Hess's Law of Constant Heat Summation. The chapter then moves to the concept of spontaneity, introducing the Second Law of Thermodynamics and entropy (ΔS) as a measure of disorder. Finally, Gibbs free energy (ΔG) is defined as the ultimate criterion for determining the spontaneity of a process under constant temperature and pressure.
7. Equilibrium
This chapter describes the state of equilibrium, a dynamic condition in reversible reactions where forward and reverse reaction rates become equal. It covers chemical equilibrium, introducing the law of mass action and the equilibrium constant (Kc and Kp). A crucial tool, Le Chatelier's principle, is explained to predict how an equilibrium system responds to changes in concentration, temperature, or pressure. The second part of the chapter focuses on ionic equilibrium in aqueous solutions. It discusses theories of acids and bases, the concept of pH, ionization of weak electrolytes, hydrolysis of salts, buffer solutions (which resist pH change), and the solubility product (Ksp) for sparingly soluble salts.
8. Redox Reactions
This chapter focuses on redox reactions, which involve the transfer of electrons. It defines oxidation (loss of electrons) and reduction (gain of electrons) and introduces the concept of oxidation number as a tool to track electron shifts in reactions. A major focus of the chapter is on the systematic methods for balancing redox reactions, both in acidic and basic media, using the oxidation number method and the ion-electron (half-reaction) method. The chapter also provides an introduction to electrochemistry by discussing electrochemical cells, where spontaneous redox reactions are used to generate electricity (galvanic cells).
9. Hydrogen
This chapter is devoted to the study of hydrogen, the simplest and most abundant element. It discusses its unique position in the periodic table, its isotopes (protium, deuterium, tritium), and its preparation and properties. A significant portion of the chapter is dedicated to its most important compound, water, covering its structure, amphoteric nature, and the concept of hard and soft water, along with methods for removing hardness. Another key compound, hydrogen peroxide (H₂O₂), is discussed in terms of its structure and its dual role as an oxidizing and reducing agent. The chapter also covers various types of hydrides and explores the potential of hydrogen as a clean fuel (hydrogen economy).
10. The S-Block Elements
This chapter provides a detailed examination of the s-block elements, which include the Alkali Metals (Group 1) and the Alkaline Earth Metals (Group 2). It discusses their general electronic configuration and explores the periodic trends in their physical and chemical properties, such as atomic radii, ionization enthalpy, and reactivity. The chapter explains the characteristic flame colorations and the reasons for the anomalous behaviour of the first element of each group (Lithium and Beryllium). It also covers the preparation, properties, and uses of commercially important compounds like sodium carbonate (Solvay process), sodium hydroxide, and calcium sulphate (Plaster of Paris).
11. The P-Block Elements
This chapter introduces the chemistry of the p-block elements, focusing on Group 13 (Boron family) and Group 14 (Carbon family) as per the Class 11 syllabus. It discusses the general trends in their electronic configuration, atomic properties, and oxidation states, highlighting phenomena like the inert pair effect. For Group 13, it delves into the chemistry of Boron and its compounds, such as borax, boric acid, and diborane. For Group 14, it explores the unique property of Carbon (catenation), its allotropes (diamond, graphite), and important compounds of carbon and silicon, including silicones and silicates. The chapter emphasizes the significant variation in properties within these groups.
12. Organic Chemistry: Some Basic Principles And Techniques
This chapter lays the groundwork for the study of organic chemistry. It starts with the classification of organic compounds and the rules of IUPAC nomenclature for systematic naming. The concept of isomerism (structural and stereoisomerism) is introduced. It provides a deep dive into the fundamental concepts of reaction mechanisms, including bond fission, reactive intermediates (carbocations, free radicals), and the electronic effects (inductive effect, resonance) that influence a molecule's reactivity. The chapter also covers essential practical aspects, including methods for the purification and both qualitative and quantitative analysis of organic compounds.
13. Hydrocarbons
This chapter is dedicated to hydrocarbons, the simplest organic compounds. It classifies them into saturated (Alkanes) and unsaturated (Alkenes and Alkynes) aliphatic hydrocarbons, and Aromatic hydrocarbons. For each class, the chapter discusses their nomenclature, isomerism, preparation methods, and characteristic chemical reactions. This includes substitution reactions for alkanes, electrophilic addition reactions for alkenes and alkynes (including Markonikov’s rule), and conformational analysis. A key section is devoted to Benzene and aromaticity, explaining its unique stability and its characteristic electrophilic substitution reactions.
14. Environmental Chemistry
This chapter applies chemical principles to understand and address environmental issues. It details various types of environmental pollution, including atmospheric, water, and soil pollution. It explains the chemistry behind major environmental threats like acid rain, the greenhouse effect and global warming, and the depletion of the stratospheric ozone layer. The chapter discusses common water pollutants and concepts like Biochemical Oxygen Demand (BOD). It also highlights strategies for pollution control and introduces the concept of Green Chemistry as a sustainable approach to chemical design and manufacturing, aiming to minimize pollution at its source.
Sample Paper
This entry provides a comprehensive Sample Paper tailored for the Class 11 Chemistry curriculum. It is an invaluable resource for students to practice and self-assess their knowledge across all 14 chapters. The paper includes a variety of question formats, designed to test both conceptual understanding and problem-solving skills. By working through this sample paper, students can familiarize themselves with the examination pattern, learn effective time management, identify areas that require further study, and build the confidence needed to excel in their final assessments. It serves as a crucial final step in a thorough revision plan.