Which of these molecules has an overall dipole moment?
A) PF₃
B) BeF₂
C) PF₅
D) CF₄
E) SF₆
IMAT 2023 · Question 44
Q44 - Polarity and electronegativity
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The correct answer is A) PF₃.
A molecule has a dipole only if its bond dipoles don't cancel, which comes down to shape.
PF₃ is pyramidal, like NH₃, because phosphorus has a lone pair, so the dipoles don't cancel. The others are all symmetrical: BeF₂ is linear, PF₅ trigonal bipyramidal, CF₄ tetrahedral and SF₆ octahedral, so their dipoles cancel out.
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