Chapter 8.3, Problem 28LC

Interpretation Introduction

Interpretation:

The geometric shape of the ${\text{BF}}_{\text{4}}^{\text{-}}$ ion is to be determined.

Concept introduction:

The positioning of the electron pairs around the main atom determines the shape of a molecule or ion. The only thing left to do is count the number of electron pairs present at the bonding level and arrange them so that there is the least possible repulsion between them.

Answer to Problem 28LC

The geometry of ${\text{BF}}_{\text{4}}^{\text{-}}$ an anion is tetrahedral.

Explanation of Solution

As the concepts of valence bond theory, the boron atom in ${\text{BF}}_{\text{3}}$ molecule is ${\text{sp}}^{\text{2}}$ hybridized. As of them is $\text{2s}$ and two $\text{2p}$ orbitals hybridize to form three ${\text{sp}}^{\text{2}}$ hybrid orbitals.

So, we can say that the molecular geometry of $B{F}_3$ molecule is trigonal planar.

But in $B{F}_4^{-}$ ion, the boron atom is ${\text{sp}}^{\text{3}}$ hybridized, as it makes four ${\text{sp}}^{\text{3}}$ hybrid hybridization $\text{2s}$ and three $\text{2p}$ orbitals.

So the molecular geometry of ${\text{BF}}_{\text{4}}^{\text{-}}$ an anion is tetrahedral.

Conclusion

The molecular geometry of any ion depends on the valence bond theory.