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Chapter Analysis
Intermediate34 pages • EnglishQuick Summary
The chapter on Chemical Bonding and Molecular Structure provides a detailed exploration of how atoms combine to form molecules. It introduces key theories such as the Kössel-Lewis approach, the Valence Shell Electron Pair Repulsion (VSEPR) Theory, the Valence Bond (VB) Theory, and Molecular Orbital (MO) Theory. These theories explain why atoms bond, the types of bonds they form, and the resulting molecular geometries. The chapter also covers concepts such as hybridization, hydrogen bonding, and resonance, providing a comprehensive view of chemical bonding.
Key Topics
- •Kössel-Lewis concept of bonding
- •Valence Shell Electron Pair Repulsion (VSEPR) Theory
- •Valence Bond Theory
- •Molecular Orbital Theory
- •Hybridization of atomic orbitals
- •Types of chemical bonds: ionic, covalent
- •Resonance in molecules
- •Hydrogen bonding
Learning Objectives
- ✓Understand the Kössel-Lewis approach to chemical bonding
- ✓Explain the octet rule and its limitations
- ✓Describe the formation of various types of chemical bonds
- ✓Use VSEPR theory to determine molecular geometry
- ✓Differentiate between valence bond and molecular orbital theories
- ✓Understand and apply the concept of hybridization
Questions in Chapter
Explain the formation of a chemical bond.
Page 133
Write Lewis dot symbols for atoms of the following elements: Mg, Na, B, O, N, Br.
Page 133
Write Lewis symbols for the following atoms and ions: S and S2–; Al and Al3+; H and H–.
Page 133
Draw the Lewis structures for the following molecules and ions: H2S, SiCl4, BeF2, CO3 2−, HCOOH.
Page 133
Define octet rule. Write its significance and limitations.
Page 134
Write the favourable factors for the formation of ionic bond.
Page 134
Discuss the shape of the following molecules using the VSEPR model: BeCl2, BCl3, SiCl4, AsF5, H2S, PH3.
Page 134
Although geometries of NH3 and H2O molecules are distorted tetrahedral, bond angle in water is less than that of ammonia. Discuss.
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How do you express the bond strength in terms of bond order?
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Define the bond length.
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Explain the important aspects of resonance with reference to the CO3 2− ion.
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H3PO3 can be represented by structures 1 and 2 shown below. Can these two structures be taken as the canonical forms of the resonance hybrid representing H3PO3? If not, give reasons for the same.
Page 134
Write the resonance structures for SO3, NO2 and NO3 −.
Page 134
Use Lewis symbols to show electron transfer between the following atoms to form cations and anions: (a) K and S (b) Ca and O (c) Al and N.
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Although both CO2 and H2O are triatomic molecules, the shape of H2O molecule is bent while that of CO2 is linear. Explain this on the basis of dipole moment.
Page 134
Write the significance/applications of dipole moment.
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Define electronegativity. How does it differ from electron gain enthalpy?
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Explain with the help of suitable example polar covalent bond.
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Arrange the bonds in order of increasing ionic character in the molecules: LiF, K2O, Na2
Page 134
Additional Practice Questions
What is the significance of lone pairs in determining the shape of a molecule?
mediumAnswer: Lone pairs are non-bonding pairs of electrons that can influence the shape of molecules due to electron pair repulsion, as seen in VSEPR theory. Their presence can lead to deviations from ideal bond angles, contributing to the molecular geometry.
How do hybridization and molecular shape correlate?
hardAnswer: Hybridization describes the mixing of atomic orbitals to form new hybrid orbitals, which can hold electrons in a molecular geometry. The type of hybridization (e.g., sp3, sp2, sp) determines the geometry of the molecule, such as tetrahedral, trigonal planar, or linear.
Discuss the differences between sigma and pi bonds.
mediumAnswer: Sigma bonds (σ) are strong covalent bonds formed by head-on overlapping of atomic orbitals, while pi bonds (π) are weaker bonds formed by the side-to-side overlap of p orbitals. Sigma bonds allow free rotation around the bond axis, whereas pi bonds restrict rotation.
Explain the concept of resonance and its importance in chemical bonding.
hardAnswer: Resonance describes the delocalization of electrons across several structures (resonance forms), which stabilizes the molecule. It's significant in molecules like benzene and ions like nitrate, where multiple valid Lewis structures exist, contributing to properties like stability and reactivity.
Why is VSEPR theory useful in predicting molecular shapes?
easyAnswer: VSEPR (Valence Shell Electron Pair Repulsion) theory is useful because it considers the repulsions between pairs of electrons around a central atom to predict the geometry of a molecule, accounting for both bonding pairs and lone pairs.
What role does electronegativity play in bond formation?
mediumAnswer: Electronegativity influences bond type and polarity; differences in electronegativity between atoms lead to polar covalent or ionic bonds. It can predict the distribution of electrons in a molecule, influencing reactivity and boiling/melting points.
How does the octet rule guide the formation of chemical bonds?
easyAnswer: The octet rule states that atoms tend to form bonds to have eight electrons in their valence shell, achieving a stable configuration. This principle helps explain why elements form certain bonds, such as covalent or ionic, to fulfill their valence requirements.
Describe how molecular orbital theory provides a different explanation of chemical bonding compared to valence bond theory.
hardAnswer: Molecular Orbital (MO) theory explains bonding by considering atomic orbitals merging to form molecular orbitals, which can be spread over the entire molecule. Unlike Valence Bond (VB) theory that views bonds as localized between pairs of atoms, MO theory can explain phenomena like bonding in homonuclear diatomic molecules and delocalized electrons.
What is the role of bond angles in molecular geometry?
mediumAnswer: Bond angles determine the shape and geometry of a molecule by indicating the spatial arrangement of bonds around a central atom, influencing properties like polarity, reactivity, and interaction types with other molecules.
Why are hydrogen bonds significant in biological molecules?
hardAnswer: Hydrogen bonds are crucial in biological molecules because they contribute to the structure and stability of compounds like DNA and proteins, affecting folding, base pairing, and overall molecular interactions within cells.