The C-F bond is more polar than the N-F bond, but CF4 molecules are nonpolar and NF3 molecules are polar. Explain why.
The Correct Answer and Explanation is:
The C–F bond is more polar than the N–F bond because fluorine is much more electronegative than both carbon and nitrogen, but the difference in electronegativity between carbon and fluorine is greater than that between nitrogen and fluorine. However, CF₄ (carbon tetrafluoride) is a nonpolar molecule, while NF₃ (nitrogen trifluoride) is a polar molecule. This difference arises from the molecular geometry and the distribution of electron pairs around the central atom.
CF₄ has a tetrahedral geometry, where the four fluorine atoms are symmetrically arranged around the central carbon atom. Although each C–F bond is highly polar, the dipole moments cancel out due to the symmetry of the molecule. As a result, CF₄ has no net dipole moment, making it a nonpolar molecule.
On the other hand, NF₃ has a trigonal pyramidal geometry, similar to ammonia (NH₃), due to the presence of a lone pair of electrons on the nitrogen atom. This lone pair pushes the three N–F bonds downward, creating an asymmetric shape. Because of this asymmetry, the dipole moments of the N–F bonds do not cancel out, and the molecule has a net dipole moment, making NF₃ a polar molecule.
Furthermore, the lone pair on nitrogen in NF₃ contributes to the overall molecular polarity, while carbon in CF₄ has no lone pairs, maintaining perfect symmetry. Even though the individual C–F bonds are more polar than N–F bonds, the three-dimensional shape of the molecule determines the overall polarity.
In conclusion, CF₄ is nonpolar due to its symmetrical tetrahedral shape that allows bond dipoles to cancel, while NF₃ is polar because of its trigonal pyramidal shape and the lone pair on nitrogen that prevents dipole cancellation. Molecular geometry is the key factor that explains the difference in polarity between these two compounds.
