Multiple Choice
Which of the following best describes the polarity of the molecule AsF_5?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Is NH_3 (ammonia) a polar molecule?
A
No, because NH_3 is a nonpolar molecule due to its symmetrical geometry.
B
Yes, because it has a trigonal pyramidal shape with a lone pair on nitrogen, resulting in a net dipole moment.
C
No, because all the N-H bonds are identical and cancel out any dipole moment.
D
Yes, because nitrogen is less electronegative than hydrogen.
Verified step by step guidance1
Step 1: Understand the molecular geometry of NH_3. Ammonia has a central nitrogen atom bonded to three hydrogen atoms and one lone pair of electrons. This arrangement leads to a trigonal pyramidal shape rather than a symmetrical shape like trigonal planar or tetrahedral without lone pairs.
Step 2: Recall 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 pointing from hydrogen to nitrogen.
Step 3: Analyze the effect of the lone pair on nitrogen. The lone pair occupies space and pushes the bonded hydrogen atoms downward, causing the molecule to be asymmetrical. This asymmetry means the bond dipoles do not cancel out.
Step 4: Combine the bond dipoles vectorially. Because of the trigonal pyramidal shape and the lone pair, the dipole moments add up to a net dipole moment pointing toward the nitrogen atom.
Step 5: Conclude that NH_3 is a polar molecule due to its trigonal pyramidal geometry and the presence of a lone pair on nitrogen, which results in a net dipole moment.
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