Multiple Choice
Which of the following molecules is polar?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following statements correctly describes the molecular polarity of PF3 and PCl3?
A
PF3 is polar, but PCl3 is nonpolar due to the difference in atomic sizes.
B
PF3 is nonpolar, while PCl3 is polar because chlorine is more electronegative than fluorine.
C
Both PF3 and PCl3 are polar molecules due to their trigonal pyramidal geometry and the presence of a lone pair on phosphorus.
D
Both PF3 and PCl3 are nonpolar because their bond dipoles cancel out.
Verified step by step guidance1
Step 1: Identify the molecular geometry of both PF3 and PCl3. Both molecules have a central phosphorus atom bonded to three halogen atoms and one lone pair, resulting in a trigonal pyramidal shape.
Step 2: Understand that molecular polarity depends on both the shape of the molecule and the difference in electronegativity between the central atom and the surrounding atoms. The presence of a lone pair on phosphorus creates an asymmetrical shape, which usually leads to a net dipole moment.
Step 3: Compare the electronegativities of fluorine and chlorine relative to phosphorus. Fluorine is more electronegative than chlorine, but in both molecules, the P–X bonds are polar, and the bond dipoles do not cancel out due to the trigonal pyramidal geometry.
Step 4: Conclude that because of the lone pair and the asymmetrical arrangement of bonds, both PF3 and PCl3 have net dipole moments, making them polar molecules.
Step 5: Recognize that statements claiming nonpolarity due to atomic size differences or bond dipole cancellation are incorrect because the molecular geometry and electronegativity differences lead to polarity in both cases.
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