Which of the following AF3 molecules will have a nonzero dipole moment?

• A. AlF3
• B. CF3
• C. NF3
• D. BF3

Answer: (C)

Verified step by step guidance

1. Step 1: Understand that the dipole moment of a molecule depends on both the polarity of individual bonds and the molecular geometry (shape). Even if bonds are polar, the overall dipole moment can be zero if the molecular geometry causes the bond dipoles to cancel out.
2. Step 2: Analyze the molecular geometry of each molecule. For example, BF3 and AlF3 have trigonal planar geometry, where the three bond dipoles are symmetrically arranged and cancel each other, resulting in a zero dipole moment.
3. Step 3: Consider NF3, which has a trigonal pyramidal shape due to the lone pair on nitrogen. This asymmetry means the bond dipoles do not cancel, leading to a nonzero dipole moment.
4. Step 4: For CF3, note that it is not a complete molecule by itself; CF3 is typically a radical or a substituent group, so it does not have a defined molecular dipole moment as a standalone molecule.
5. Step 5: Conclude that among the given options, NF3 has a nonzero dipole moment because of its molecular geometry and bond polarity, while BF3 and AlF3 have zero dipole moments due to their symmetrical trigonal planar shapes.