Multiple Choice
Which of the following best describes the polarity of an NH_3 (ammonia) molecule?
13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following molecules contains polar covalent bonds but is a nonpolar molecule?
A
NH3
B
H2O
C
CHCl3
D
CO2
Verified step by step guidance1
Step 1: Understand the difference between polar covalent bonds and molecular polarity. A polar covalent bond occurs when two atoms share electrons unequally due to differences in electronegativity, creating partial positive and negative charges within the bond.
Step 2: Recognize that a molecule can have polar bonds but still be nonpolar overall if the molecular geometry causes the bond dipoles to cancel out. This happens when the molecule is symmetrical.
Step 3: Analyze the molecular geometry of each molecule: NH3 (trigonal pyramidal), H2O (bent), CHCl3 (tetrahedral but asymmetrical due to different atoms), and CO2 (linear).
Step 4: Determine the polarity of each molecule by considering both bond polarity and shape. NH3 and H2O have polar bonds and asymmetrical shapes, making them polar molecules. CHCl3 has polar bonds and an asymmetrical shape, so it is polar.
Step 5: Note that CO2 has polar covalent bonds (between C and O) but is linear and symmetrical, so the bond dipoles cancel out, making CO2 a nonpolar molecule despite having polar bonds.
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