Multiple Choice
Which of the following best explains why BeF_2 is a nonpolar molecule?
13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following molecules is polar?
A
CO_2
B
NH_3
C
CCl_4
D
CH_4
Verified step by step guidance1
Step 1: Understand that molecular polarity depends on both the polarity of individual bonds and the geometry of the molecule. A molecule is polar if it has a net dipole moment, meaning the dipoles do not cancel out.
Step 2: Analyze the molecular geometry of each molecule using VSEPR theory: CO_2 is linear, NH_3 is trigonal pyramidal, CCl_4 is tetrahedral, and CH_4 is tetrahedral.
Step 3: Consider the electronegativity differences and bond dipoles: CO_2 has polar C=O bonds, NH_3 has polar N-H bonds, CCl_4 has polar C-Cl bonds, and CH_4 has C-H bonds which are considered nonpolar or very weakly polar.
Step 4: Determine if the molecular geometry allows dipoles to cancel: In CO_2 and CCl_4, the symmetrical shape causes bond dipoles to cancel, making them nonpolar overall. In NH_3, the trigonal pyramidal shape causes dipoles to not cancel, resulting in a polar molecule.
Step 5: Conclude that NH_3 is polar because it has polar bonds and an asymmetrical shape that leads to a net dipole moment, unlike the other molecules listed.
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