Multiple Choice
Which of the following best describes the polarity of a nitrogen molecule (N_2)?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following best describes the polarity of boron trichloride (BCl_3)?
A
BCl_3 is a polar molecule because the B–Cl bonds are polar and the molecule has a net dipole moment.
B
BCl_3 is a polar molecule because it contains chlorine atoms, which are highly electronegative.
C
BCl_3 is a nonpolar molecule because its molecular geometry is trigonal planar and the dipoles cancel out.
D
BCl_3 is a nonpolar molecule because all the atoms are identical.
Verified step by step guidance1
Identify the molecular geometry of boron trichloride (BCl\_3). Since boron is bonded to three chlorine atoms and has no lone pairs, the shape is trigonal planar.
Determine the polarity of each B–Cl bond by considering the difference in electronegativity between boron and chlorine. Chlorine is more electronegative, so each B–Cl bond is polar with a dipole moment pointing toward chlorine.
Analyze the symmetry of the molecule. In a trigonal planar geometry, the three B–Cl bond dipoles are arranged 120° apart in a plane, which causes the individual dipoles to cancel each other out.
Conclude that because the bond dipoles cancel due to the symmetrical trigonal planar shape, the overall molecule has no net dipole moment and is therefore nonpolar.
Review the answer choices and select the one that correctly states that BCl\_3 is nonpolar due to its trigonal planar geometry and cancellation of dipoles.
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