In Class 11 Final Exams there will be Case studies and Passage Based Questions will be asked, So practice these types of questions. Study Rate is always there to help you. Free PDF Downloads of CBSE Class 11 Chemistry Chapter 4 Case Study and Passage-Based Questions with Answers were Prepared Based on the Latest Exam Pattern. Students can solve Class 11 Chemistry Case Study Questions Chemical Bonding and Molecular Structure to know their preparation level.

In CBSE Class 11 Chemistry Paper, There will be a few questions based on case studies and passage-based as well. In that, a paragraph will be given, and then the MCQ questions based on it will be asked.

Chemical Bonding and Molecular Structure Case Study Questions With Answers

Here, we have provided case-based/passage-based questions for Class 11 Chemistry Chapter 4 Chemical Bonding and Molecular Structure

Case Study/Passage-Based Questions

Case Study 1: Lewis dot structures, in general, do not represent the actual shapes of the molecules. In the case of polyatomic ions, the net charge is possessed by the ion as a whole and not by a particular atom. It is, however, feasible to assign a formal charge to each atom. The formal charge of an atom in a polyatomic molecule or ion may be defined as the difference between the number of valence electrons of that atom in an isolated or free state and the number of electrons assigned to that atom in the Lewis structure. It is expressed as : Generally the lowest energy structure is the one with the smallest formal charges on the atoms. The formal charge is a factor based on a pure covalent view of bonding in which electron pairs are shared equally by neighboring atoms. The octet rule, though useful, is not universal. It is quite useful for understanding the structures of most organic compounds and it applies mainly to the second-period elements of the periodic table. There are three types of exceptions to the octet rule.

• The incomplete octet of the central atom
• Odd-electron molecules
• The expanded octetFrom the Kössel and Lewis treatment of the formation of an ionic bond, it follows that the formation of ionic compounds would primarily depend upon the:
• The ease of formation of the positive and negative ions from the respective neutral atoms;
• The arrangement of the positive and negative ions in the solid, that is the lattice of the crystalline compound.

The Lattice Enthalpy of an ionic solid is defined as the energy required to completely separate one mole of a solid ionic compound into gaseous constituent ions. For example, the lattice enthalpy of NaCl is 788 kJ mol^–1. This means that 788 kJ of energy is required to separate one mole of solid NaCl into one mole of Na⁺  (g) and one mole of Cl^– (g) to an infinite distance. Bond length is defined as the equilibrium distance between the nuclei of two bonded atoms in a molecule. Bond lengths are measured by spectroscopic, X-ray diffraction, and electron-diffraction techniques. The covalent radius is measured approximately as the radius of an atom’s-core which is in contact with the core of an adjacent atom in a bonded situation.  The van der Waals radius represents the overall size of the atom which includes its valence shell in a nonbonded situation.  The bond Angle is defined as the angle between the orbitals containing bonding electron pairs around the central atom in a molecule/complex ion. Bond angle is expressed in degree which can be experimentally determined by spectroscopic methods. It gives some idea regarding the distribution of orbitals around the central atom in a molecule/complex ion and hence it helps us in determining its shape. For example H–O–H bond angle in water can be represented as under :

Bond Enthalpy It is defined as the amount of energy required to break one mole of bonds of a particular type between two atoms in a gaseous state. The unit of bond enthalpy is kJ mol^–1. For example, the H–H bond enthalpy in hydrogen molecules is 435.8 kJ mol–1. H2 (g) → H(g) + H(g); ∆aH  = 435.8 kJ mol–1. Bond OrderIn the Lewis description of a covalent bond, the Bond Order is given by the number of bonds between the two atoms in a molecule. The bond order, for example in H2(with a single shared electron pair), in O2(with two shared electron pairs), and in N2(with three shared electron pairs) is 1,2,3respectively. A general correlation is useful for understanding the stabilities of molecules that: with an increase in bond order, bond enthalpy increases and bond length decreases. The concept of resonance was introduced to deal with the type of difficulty experienced in the depiction of accurate structures of molecules like O3. According to the concept of resonance, whenever a single Lewis structure cannot describe a molecule accurately, a number of structures with similar energy, positions of nuclei, bonding, and non-bonding pairs of electrons are taken as the canonical structures of the hybrid which describes the molecule accurately.

Thus for O₃, the two structures shown above constitute the canonical structures or resonance structures, and their hybrid i.e., the structure represents the structure of O3 more accurately. This is also called a resonance hybrid. Resonance is represented by a double-headed arrow. In general, it may be stated that

• Resonance stabilizes the molecule as the energy of the resonance hybrid is less than the energy of any single canonical structure; and,
• Resonance averages the bond characteristics as a whole. Thus the energy of the theO3resonancehybrid is lower than either of the two canonical forms I and II.

[A] MCQ

1) Which of the following techniques is used to measure bond length?

• (a) spectroscopic techniques
• (b) X-ray diffraction
• (c) electron-diffraction techniques
• (d) All the above

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2) The unit of bond enthalpy is …

• (a) kJ mol^–1
• (b) Cal mol^-1
• (c) Cal mol
• (d) kJ mol

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3) With the increase in bond order, bond enthalpy … and bond length ….

• (a) decreases, decreases
• (b) increases decreases
• (c) increases, increases
• (d) decreases, increases

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4) The …. is measured approximately as the radius of an atom’s core which is in contact with the core of an adjacent atom in a bonded situation.

• (a) ionic radius
• (b) Metallic radius
• (c) covalent radius
• (d) None of above

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5) … is given by the number of bonds between the two atoms in a molecule.

• (a) Bond Order
• (b) Bond size
• (c) Bond enthalpy
• (d) Bond angle

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What is the formal charge of an atom in a polyatomic molecule or ion?
A) The number of covalent bonds in the atom
B) The difference between the valence electrons in an isolated atom and the electrons in the Lewis structure
C) The energy required to break one mole of bonds
D) The distance between two bonded atoms

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Which of the following is NOT an exception to the octet rule?
A) The expanded octet
B) Odd-electron molecules
C) Incomplete octet of the central atom
D) Bond angle

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The lattice enthalpy of NaCl is defined as:
A) The energy to convert NaCl into its gaseous form
B) The energy to separate one mole of NaCl into Na+ (g) and Cl– (g) to an infinite distance
C) The energy to form one mole of NaCl from Na and Cl
D) The energy to break one Na-Cl bond

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What is the bond order for O2 according to Lewis structures?
A) 1
B) 2
C) 3
D) 4

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