Multiple Choice
Which of the following molecules is nonpolar?
13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following best describes the polarity of the molecule NH_3 (ammonia)?
A
NH_3 is polar only when dissolved in water.
B
NH_3 is a nonpolar molecule because its dipoles cancel out due to its symmetrical shape.
C
NH_3 is nonpolar because it contains only nonpolar covalent bonds.
D
NH_3 is a polar molecule because it has a trigonal pyramidal shape and a net dipole moment.
Verified step by step guidance1
Identify the molecular geometry of NH_3 (ammonia). Ammonia has a central nitrogen atom bonded to three hydrogen atoms and one lone pair of electrons, which gives it a trigonal pyramidal shape.
Understand that molecular polarity depends on both the polarity of individual bonds and the shape of the molecule. Each N-H bond is polar because nitrogen is more electronegative than hydrogen, creating bond dipoles.
Analyze the symmetry of the molecule. The trigonal pyramidal shape is asymmetrical due to the lone pair on nitrogen, which means the bond dipoles do not cancel out.
Determine the net dipole moment. Because the bond dipoles do not cancel, NH_3 has a net dipole moment pointing from the hydrogen atoms toward the nitrogen atom, making the molecule polar.
Conclude that NH_3 is polar regardless of the solvent because its molecular shape and bond polarity create an overall dipole moment, so the correct description is that NH_3 is a polar molecule with a trigonal pyramidal shape and a net dipole moment.
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