Chapter 7, Problem 7.1KSP

Interpretation Introduction

Interpretation:

The molecular geometry of ${\text{PBr}}_{\text{3}}$ should be identified from the given options.

Concept introduction:

• Electron domain is the term used to indicate lone pair and bond pair of electrons.
• Lewis structures is also known as Lewis dot structures which represents the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.
• In VSEPR, the geometry of the molecule is explained based on minimizing electrostatic repulsion between the molecules’ valence electrons around a central atom
• Electro-domain geometry includes both bond pairs and lone pairs of central atom for determining the geometry of molecule.
• Molecular geometry includes only the bond pairs of central atom for determining the geometry of the molecule.

Correct answer:

Trigonal pyramidal

Explanation of Solution

Reason for correct option

To determine: the electron-domain geometry and molecular geometry of ${\text{PBr}}_{\text{3}}$.

Trigonal pyramidal

In ${\text{PBr}}_{\text{3}}$ molecule,

Three bromine atoms are bonded to phosphorus atom. So phosphorus is the central atom in this molecule.

A Lewis structure represents the bonding between atoms of a molecule and the lone pairs of electrons that may exist in the molecule.

Therefore,

The Lewis structure of ${\text{PBr}}_{\text{3}}$ molecule is,

According to VSEPR theory, the geometry of the molecule is explained based on minimizing electrostatic repulsion between the molecules’ valence electrons around a central atom

The Lewis structure of ${\text{PBr}}_{\text{3}}$ molecule shows, there are fourelectron domains, in which three are bond pairs and one is lone pair.

Electro-domain geometry includes both bond pairs and lone pairs of central atom for determining the geometry of molecule.

Therefore,

The electron-domain geometry of ${\text{PBr}}_{\text{3}}$ is tetrahedral.

Molecular geometry includes only the bond pairs of central atom for determining the geometry of the molecule.

Therefore,

The molecular geometry of ${\text{PBr}}_{\text{3}}$ is predicted to be trigonal planar, but the geometry is trigonal pyramidal, because the repulsion of lone pair on three bonds distorted the planarity of trigonal planar.

Hence the correct option for molecular geometry of ${\text{PBr}}_{\text{3}}$ is option c.

Reasons for incorrect options:

Writes all the molecular geometry of ${\text{PBr}}_{\text{3}}$ given in the options except option c.

(a) Trigonal planar

(b) Tetrahedral

(d) Bent

(e) T-shaped

The molecular geometry of ${\text{PBr}}_{\text{3}}$ is found as trigonal pyramidal.

So, this molecular geometry of ${\text{PBr}}_{\text{3}}$ is not matching with any of the above geometries of ${\text{PBr}}_{\text{3}}$ in remaining options.

Hence the incorrect options are a, b, d and e.

Conclusion

Conclusion

The correct optionfor molecular geometry of ${\text{PBr}}_{\text{3}}$ is identified from the given options. The correct molecular geometry of ${\text{PBr}}_{\text{3}}$ is determined by using Lewis and VSEPR theory.