Multiple Choice
Which of the following molecules contains polar covalent bonds but is a nonpolar molecule?
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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 BF_3?
A
BF_3 is a nonpolar molecule because its trigonal planar geometry causes the dipole moments to cancel.
B
BF_3 is a polar molecule because it contains three fluorine atoms.
C
BF_3 is a nonpolar molecule because boron and fluorine have similar electronegativities.
D
BF_3 is a polar molecule because the B–F bonds are polar and the molecule has a net dipole moment.
Verified step by step guidance1
Step 1: Identify the molecular geometry of BF_3. BF_3 has three bonding pairs around the central boron atom and no lone pairs, which gives it a trigonal planar shape.
Step 2: Understand the concept of bond polarity. The B–F bonds are polar because fluorine is more electronegative than boron, creating dipole moments pointing from boron to fluorine.
Step 3: Analyze the symmetry of the molecule. In a trigonal planar geometry, the three B–F bond dipoles are arranged 120° apart, symmetrically around the central atom.
Step 4: Determine the net dipole moment. Because the dipole moments are equal in magnitude and symmetrically spaced, they cancel each other out, resulting in no net dipole moment.
Step 5: Conclude the molecular polarity. Since the dipole moments cancel, BF_3 is a nonpolar molecule despite having polar bonds.
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