Multiple Choice
Which of the following Lewis structures represents a molecule that is polar?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following molecules is polar?
A
NH_3
B
BF_3
C
CO_2
D
CCl_4
Verified step by step guidance1
Step 1: Understand that molecular polarity depends on both the polarity of individual bonds and the geometry (shape) of the molecule, which affects how bond dipoles add up.
Step 2: Analyze the molecular geometry of each molecule using VSEPR theory: NH_3 is trigonal pyramidal, BF_3 is trigonal planar, CO_2 is linear, and CCl_4 is tetrahedral.
Step 3: Consider the electronegativity differences between atoms to determine if bonds are polar. For example, N-H bonds in NH_3 are polar, B-F bonds in BF_3 are polar, C=O bonds in CO_2 are polar, and C-Cl bonds in CCl_4 are polar.
Step 4: Evaluate the symmetry of each molecule to see if the bond dipoles cancel out. In BF_3, CO_2, and CCl_4, the symmetrical shapes cause the dipoles to cancel, resulting in nonpolar molecules.
Step 5: Recognize that NH_3 has a trigonal pyramidal shape with a lone pair on nitrogen, causing an asymmetrical distribution of charge and a net dipole moment, making NH_3 polar.
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