Multiple Choice
Which of the following molecules is nonpolar even though it contains polar bonds?
13. Liquids, Solids & Intermolecular Forces
Molecular Polarity
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Which of the following best explains why BeF_2 is a nonpolar molecule?
A
BeF_2 has a linear molecular geometry, causing the dipole moments of the Be–F bonds to cancel each other out.
B
BeF_2 is nonpolar due to the presence of lone pairs on the central atom.
C
BeF_2 is nonpolar because beryllium and fluorine have similar electronegativities.
D
BeF_2 contains only nonpolar covalent bonds between Be and F.
Verified step by step guidance1
Step 1: Identify the molecular geometry of BeF_2 by considering the number of bonding pairs and lone pairs around the central atom (beryllium). Since Be forms two bonds and has no lone pairs, the molecular geometry is linear.
Step 2: Understand that each Be–F bond is polar because fluorine is more electronegative than beryllium, creating a dipole moment pointing from Be to F.
Step 3: Recognize that in a linear molecule like BeF_2, the two bond dipoles are oriented 180 degrees apart, meaning they point in exactly opposite directions.
Step 4: Apply vector addition of dipole moments: because the two dipoles are equal in magnitude and opposite in direction, they cancel each other out, resulting in no net dipole moment.
Step 5: Conclude that the cancellation of bond dipoles due to the linear geometry makes BeF_2 a nonpolar molecule, despite having polar bonds.
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