Multiple Choice
What does it mean when a molecule is said to be "polar"?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following best describes the molecular polarity of PCl_5?
A
PCl_5 is a nonpolar molecule because chlorine is less electronegative than phosphorus.
B
PCl_5 is a polar molecule because it contains polar P–Cl bonds.
C
PCl_5 is a polar molecule because it has a lone pair on the phosphorus atom.
D
PCl_5 is a nonpolar molecule because its molecular geometry is trigonal bipyramidal and the bond dipoles cancel out.
Verified step by step guidance1
Identify the molecular geometry of PCl_5 by considering the number of bonding pairs and lone pairs around the central phosphorus atom. PCl_5 has five bonding pairs and no lone pairs, leading to a trigonal bipyramidal shape.
Recall that in a trigonal bipyramidal geometry, the bond angles and spatial arrangement allow for symmetrical distribution of the five P–Cl bonds.
Understand that each P–Cl bond is polar due to the difference in electronegativity between phosphorus and chlorine, creating bond dipoles.
Analyze how the symmetrical trigonal bipyramidal shape causes the individual bond dipoles to cancel each other out because they are oriented in such a way that their vector sum is zero.
Conclude that despite having polar bonds, the overall molecule is nonpolar because the molecular geometry leads to cancellation of bond dipoles, resulting in no net dipole moment.
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