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Ch.9 - Molecular Geometry and Bonding Theories
All textbooksBrown 15th EditionCh.9 - Molecular Geometry and Bonding TheoriesProblem 35
Chapter 9, Problem 35

Which of the following statements are true?
i. The overall dipole moment of a molecule is the vector sum of its individual bond dipoles.
ii. If atoms A and B in an AB𝑛 molecule have different electronegativities, then the AB𝑛 molecule must have a nonzero dipole moment.
iii. The bond dipoles in a tetrahedral AB4 molecule cancel one another.

Verified step by step guidance
1
Step 1: Understand the concept of dipole moment. The dipole moment is a measure of the separation of positive and negative charges in a molecule. It is a vector quantity, meaning it has both magnitude and direction.
Step 2: Evaluate statement i. The overall dipole moment of a molecule is indeed the vector sum of its individual bond dipoles. This means that the direction and magnitude of each bond dipole contribute to the overall dipole moment of the molecule.
Step 3: Evaluate statement ii. Consider the electronegativity difference between atoms A and B. While a difference in electronegativity suggests a polar bond, the overall dipole moment of the molecule also depends on the geometry. If the molecular geometry allows for the dipoles to cancel out, the molecule can still have a zero dipole moment.
Step 4: Evaluate statement iii. In a tetrahedral AB4 molecule, the bond dipoles can cancel each other out if the molecule is symmetrical. This is because the vector sum of the dipoles in a symmetrical tetrahedral arrangement is zero.
Step 5: Conclude which statements are true based on the evaluations. Consider the role of molecular geometry and symmetry in determining the overall dipole moment.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Dipole Moment

The dipole moment is a measure of the separation of positive and negative charges in a molecule, represented as a vector. It indicates the polarity of a bond or molecule, with a larger dipole moment signifying greater polarity. The overall dipole moment of a molecule is determined by the vector sum of all individual bond dipoles, taking into account both their magnitudes and directions.
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Electronegativity and Polarity

Electronegativity is the tendency of an atom to attract electrons in a chemical bond. When two atoms in a molecule have different electronegativities, the shared electrons are pulled closer to the more electronegative atom, creating a polar bond. If the molecule has an asymmetrical arrangement of these polar bonds, it will have a nonzero dipole moment, indicating overall molecular polarity.
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Molecular Geometry and Dipole Cancellation

The geometry of a molecule significantly affects its dipole moment. In symmetrical molecules, such as tetrahedral AB4, the bond dipoles can cancel each other out due to their equal magnitude and opposite directions. This results in a net dipole moment of zero, meaning the molecule is nonpolar despite having polar bonds.
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Related Practice
Textbook Question

Consider the following XF4 ions: PF4-, BrF4-, ClF4+, and AlF4-. (a) Which of the ions have more than an octet of electrons around the central atom?

Textbook Question

Consider the following XF4 ions: PF4-, BrF4-, ClF4+, and AlF4-. (c) Which of the ions will have an octahedral electron-domain geometry?

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Textbook Question

a. Does SCl2 have a nonzero dipole moment?

Textbook Question

(b) It turns out that ozone, O3, has a small dipole moment. How is this possible, given that all the atoms are the same?

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