Chapter 12, Problem 46A

Interpretation Introduction

Interpretation:

The reason for the geometric structure of $B{F}_3$ to be flat but that of $N{F}_3$ to be pyramidal needs to be explained.

Concept introduction:

Structure of molecule can be drawn using VSEPR theory. The total number of bonding and non-bonding pairs of electrons tells about the geometry of the molecule.

The valence electrons are the electrons present in outermost shell.

Answer to Problem 46A

3 pairs of electrons are surrounding the boron in $B{F}_3$ . Therefore, its geometric structure is trigonal planar.

4 pairs of electrons are surrounding the nitrogen in $N{F}_3$ . Therefore, its geometric structure is tetrahedral but due to presence of lone pair structure gets distorted and its shape is pyramidal.

Explanation of Solution

Lewis structure of $B{F}_3$is:

  

Structure shows, in $B{F}_3$ central atom boron has three bond pairs and no lone pair. In total it has 3 pairs of electrons. Thus, its geometry is trigonal planar according to VSEPR theory.

Lewis structure of $N{F}_3$is:

  

Structure shows, in $N{F}_3$ central atom nitrogen has three bond pairs and one lone pair. In total it has 4 pairs of electrons. Thus, its geometry is tetrahedral but shape is pyramidal according to VSEPR theory.

Conclusion

Thus, $B{F}_3$ is trigonal planar and $N{F}_3$ is pyramidal although both having same number of atoms.