Multiple Choice
In a water molecule (H_2O), which end of the molecule has a slightly positive charge?
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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 phosphorus pentachloride (PCl_5)?
A
PCl_5 is a polar molecule because it contains polar P–Cl bonds.
B
PCl_5 is nonpolar because chlorine atoms are less electronegative than phosphorus.
C
PCl_5 is a nonpolar molecule because its molecular geometry is symmetrical.
D
PCl_5 is a polar molecule due to the presence of a lone pair on phosphorus.
Verified step by step guidance1
Identify the molecular geometry of phosphorus pentachloride (PCl_5). PCl_5 has five chlorine atoms bonded to a central phosphorus atom, and no lone pairs on phosphorus. The shape is trigonal bipyramidal.
Recall that in a trigonal bipyramidal geometry, the molecule has three atoms in an equatorial plane separated by 120° and two atoms in axial positions separated by 180°, creating a symmetrical arrangement.
Consider the polarity of individual P–Cl bonds. Each P–Cl bond is polar due to the difference in electronegativity between phosphorus and chlorine.
Analyze how the bond dipoles combine in the symmetrical trigonal bipyramidal shape. Because the dipoles are arranged symmetrically, they cancel each other out, resulting in no net dipole moment.
Conclude that despite having polar bonds, the overall molecule is nonpolar due to its symmetrical geometry, which causes the bond dipoles to cancel.
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