NCERT Solutions Class 11 Chemistry Chapter 4 Chemical Bonding And Molecular Structure - PDF Download

NCERT Solutions, in Class 12 Chemistry, Chapter 4 deals with chemical bonding and molecular structure, provides a comprehensive overview of this chapter and answers all the questions asked in the exercises. NCERT solutions class 11 chemistry - chapter 4 is designed to provide students with the necessary knowledge and understanding of the chemical bonding and molecular structure topics. To gain a comprehensive understanding of these topics, it is recommended that students access these solutions, which are written in simple language to make it easier to understand. The solutions for class 12 chemistry are prepared by eSaral’s chemistry teachers.

Once you’ve completed this unit, you’ll be able to:

• Explain the kossel-lewis approach to chemical bonding

• Understand the octet principle and its limitations

• Draw Lewis structures of simple molecules

• Explain how different types of bonds are formed

• Explain VSEPR theory and predict simple molecule geometry

• Explain valence bond approach

• Explain covalent bond formation

• Prediction of covalent bond directional properties

• Explain different types of hybridisation including s, p and d orbitals

• Draw simple covalent molecule shapes

• Explain molecular orbital theory

• Explain homo nucleic diatomic molecules

• Understand hydrogen bond

Sections Covered in Chapter 14 - Chemical Bonding and Molecular Structure

4.1 Kossel-Lewis approach to chemical bonding: There were a lot of attempts to figure out how chemical bonds are formed in terms of how many electrons they hold, but it wasn't until 1916 that scientists independently came up with a good explanation. They first came up with a way to explain valence electrons, which was based on how inert noble gases are.

Following subtopics will be discussed in this section:

• Octet rule

• Covalent bond

• Lewis representation of simple molecules

• Formal charge

• Limitations of the octet rule

4.2 Ionic or electrovalent bond: An ionic bond (or electrovalent bond) is a chemical bond formed between two atoms with very different electronegativity. An ionic bond is formed when one atom gives electrons to another, creating positively and negatively-charged ions. The ions are attracted to each other through the electrostatic attraction of their opposite charges.

Following subtopics will be discussed in this section:

• Lattice enthalpy

4.3 Bond parameters: Bond parameters describe the chemical bonds between molecules. Bond parameters tell us about the strength, bond length, and bond polarity of a molecule. They also tell us about the stability and the behavior of a molecule. Some of the most important bond parameters are:

Following subtopics will be discussed in this section:

• Bond length

• Bond angle

• Bond enthalpy

• Bond order

• Resonance structures

• Polarity of bonds

4.4 The valence shell electron pair repulsion (VSEPR) theory : Lewis' concept does not explain the shape of molecules. However, it does provide a straightforward way to predict the shape of a covalent molecule. Sidgwick (1940) and Powell (1951) proposed a straightforward theory based on the repellent interactions of the valence pairs of the atoms.

4.5 Valence Bond Theory: The theory of valence bonds was first proposed by Heitler, London and Pauling. The discussion of the theory of valence bond is based on a number of fundamental concepts, including the understanding of atomic orbits, electronic configurations of elements, overlap criteria of atomic orbits, hybridization of atomic orbits, principles of variations and superpositions.

Following subtopics will be discussed in this section: 

• Orbital overlap concept

• Directional properties of bonds

• Overlapping of atomic orbitals

• Types of overlapping and nature of covalent bonds

• Strength of sigma and pi bonds

4.6 Hybridisation: Hybridisation is the process of combining two or more molecular orbitals to create a new hybrid orbital with distinct characteristics, including shape, energy and bonding properties. Hybridization takes place when two or more atoms form a covalent bond in a molecule, and it elucidates the molecular structure and bonding patterns found in various compounds.

Following subtopics will be discussed in this section:

• Types of hybridisation 

• Other examples of sp3 , sp2 and sp   hybridisation

• Hybridisation of elements involving d orbitals

4.7 Molecular Orbital Theory: Molecular orbital theory is a theoretical framework used in chemistry to describe the behavior of the electrons in molecules. It is an extension of the concept of atomic orbital theory to include the interaction and energy levels of the entire molecule, rather than just the individual atoms. Molecular orbital theory provides a more detailed understanding of molecular bonding, electron distribution and molecular properties.

Following subtopics will be discussed in this section:

• Formation of molecular orbitals linear combination of atomic orbitals (LCAO)

• Condition for the combination of atomic orbitals

• Types of molecular orbitals

• Energy level diagram for molecular orbitals

• Electronic configuration and molecular behavior

4.8 Bonding in Some Homonuclear Diatomic Molecules: In a homonuclear diatomic molecule, two atoms from the same element join together to make a molecule. This bond is mainly explained by molecular orbital theory.

Following subtopics will be discussed in this section: 

• Hydrogen molecule

• Helium molecule

• Lithium molecule

• Carbon molecule

• Oxygen molecule

4.9 Hydrogen Bonding: Hydrogen bonding refers to an interaction between molecules in which a hydrogen atom, bonded to a high electronegativity atom (generally nitrogen, oxygen or fluorine), interacts with the lone pairs of electrons of other electronegativity atoms in other molecules. This interaction results in a relatively strong bond between molecules, and plays an essential role in a variety of chemical and physical phenomena.

Following subtopics will be discussed in this section:

• Cause of formation of hydrogen bond

• Types of hydrogen bonds

Key Points of Class 11 Chemistry NCERT Chapter 4 Chemical Bonding and Molecular Structure

• Kössel's first understanding of how electronegative and electropositive ions form was related to the process of getting the ions to form noble gas configurations. The stability of these ions is due to the electrostatic attraction between them, which gives us the idea of electrovalency.

• Covalent bonding is first described by Lewis as the sharing of electrons between atoms, and he related this process to the achievement of noble gas configurations by reacting atoms resulting from electron sharing. The Lewis dot symbols indicate the valence electron number of the atoms in a given element, and the Lewis dot structures represent the pictorial representation of bonding in a molecule.

• A crystal lattice is a three-dimensional arrangement of positive and negative ions arranged in an ordered sequence. A crystalline solid has a charge balance between positive and negative ions, and the stability of the crystal lattice is determined by the enthalpy of the lattice formation.

• It is not possible to accurately describe a collection of molecules or polyatomic ions using a single Lewis structure. Instead, a variety of representations are written on the same skeletal structure, representing the molecule or ion, and the contributing structures or canonical forms taken together form the resonance hybrid. 

• The electronic configuration of the molecules is determined by filling the molecular orbitals with electrons in the order of decreasing energy levels. The Pauli exclusion principle and Hund's rule apply to molecular orbitals, just as they do to atoms. Molecular orbitals are said to be stable when the number of electrons in the bonding molecular orbitals exceeds the number in the antibonding molecules.

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Downloading NCERT solutions for class 11 chemistry chapter 4 “Chemical bonding and molecular structure” can provide several advantages to students. Some of the main advantages include:

Concept clarity: NCERT solutions will provide clear and detailed explanations for every question and concept of the chapter. This will help students to understand the basic concepts of chemical bond and molecular structure in detail.

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Exam preparation: NCERT solutions are prepared by subject experts, taking into account the exam pattern and syllabus, which can help students to prepare for their exams better and score higher marks. 

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Frequently Asked Questions

Question 1: What is chemical bonding?

Answer 1: Chemical bonding refers to the process by which molecules or compounds are formed by the exchange, transfer, or overlapping of electrons between atoms. It involves the interaction of the outermost electrons of atoms which are known as valence electrons.

Question 2: What are the main types of chemical bonds?

Answer 2: Covalent, ionic, and metallic bonds are the most common types of chemical bonding. Covalent bonding involves sharing electrons, ionic bonding involves transferring electrons, and metallic bonding involves a “sea” of displaced electrons between positively charged metal ions.