Multiple Choice
Which of the following molecules has a net dipole moment?
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13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following molecules is polar?
A
H_2O
B
CO_2
C
CS_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 of the molecule. A molecule is polar if it has a net dipole moment, meaning the bond dipoles do not cancel out.
Step 2: Analyze the molecular geometry of each molecule using the VSEPR theory. For example, $\mathrm{H_2O}$ has a bent shape, $\mathrm{CO_2}$ and $\mathrm{CS_2}$ are linear, and $\mathrm{CCl_4}$ is tetrahedral.
Step 3: Consider the electronegativity differences between the central atom and the surrounding atoms to determine if the bonds are polar. For instance, $\mathrm{H_2O}$ has polar O-H bonds, $\mathrm{CO_2}$ has polar C=O bonds, $\mathrm{CS_2}$ has polar C=S bonds, and $\mathrm{CCl_4}$ has polar C-Cl bonds.
Step 4: Evaluate whether the molecular geometry causes the bond dipoles to cancel out. In linear molecules like $\mathrm{CO_2}$ and $\mathrm{CS_2}$, the dipoles are equal and opposite, canceling each other. In tetrahedral $\mathrm{CCl_4}$, the symmetrical arrangement also cancels dipoles.
Step 5: Conclude that $\mathrm{H_2O}$ is polar because its bent shape causes the bond dipoles to add up to a net dipole moment, making the molecule polar.
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