The BF3 molecule is nonpolar, whereas the NF3 molecule is polar. Which of the following statements a — Bonding Chemistry Question

STEPS:

1. Understand the physical chemistry of molecular polarity: A molecule's overall polarity is determined by both the individual bond dipoles (which are determined by the electronegativity differences between the bonded atoms) and the three-dimensional molecular geometry (which determines whether these individual dipoles cancel one another out or combine to produce a net dipole moment).
2. Analyze the Lewis structure and geometry of $\text{BF}_3$:
* Boron ($\text{B}$) has 3 valence electrons, and each Fluorine ($\text{F}$) has 7, totaling 24 valence electrons.
* The central boron atom forms 3 single bonds with the 3 fluorine atoms and possesses no unshared (lone) pairs of electrons.
* According to VSEPR theory, a central atom with three bonding domains and zero nonbonding domains assumes a symmetric, two-dimensional trigonal planar molecular geometry with bond angles of $120^\circ$.
* Because the three highly polar $\text{B}-\text{F}$ bond dipoles are of equal magnitude and arranged in a perfectly symmetric planar geometry, they pull in opposite directions and cancel each other out completely, resulting in a nonpolar molecule with a net molecular dipole moment of zero.
3. Analyze the Lewis structure and geometry of $\text{NF}_3$:
* Nitrogen ($\text{N}$) has 5 valence electrons, and each Fluorine ($\text{F}$) has 7, totaling 26 valence electrons.
* The central nitrogen atom forms 3 single bonds with the fluorine atoms and retains one unshared (lone) pair of electrons.
* According to VSEPR theory, a central atom with three bonding domains and one nonbonding domain assumes a three-dimensional trigonal pyramidal molecular geometry with bond angles of approximately $107^\circ$.
* Because of this nonplanar geometry, the polar $\text{N}-\text{F}$ bond dipoles do not point in symmetric opposite directions to cancel out. Instead, their downward dipoles reinforce one another, combining with the dipole contribution of the nitrogen lone pair to create a permanent net molecular dipole moment, making $\text{NF}_3$ a polar molecule.
4. Identify the correct option: The lone pair of electrons on the nitrogen atom forces $\text{NF}_3$ into a nonplanar geometry, which prevents the polar bond dipoles from canceling out. This confirms Option D is the correct answer.

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WHY_OTHERS_WRONG:

• Option A is incorrect: Both molecules feature single covalent bonds between the central atom and the fluorine atoms in their standard representations. Nitrogen does not form multiple bonds with fluorine in $\text{NF}_3$.
• Option B is incorrect: Both $\text{B}-\text{F}$ and $\text{N}-\text{F}$ bonds are highly polar because fluorine is significantly more electronegative than both boron and nitrogen. The nonpolarity of $\text{BF}_3$ is due to its symmetric geometry causing its polar bonds to cancel out, not because its bonds are nonpolar.
• Option C is incorrect: Both $\text{BF}_3$ and $\text{NF}_3$ are covalent molecular compounds consisting of nonmetals sharing electrons; neither is an ionic compound.