Chapter 16, Problem 16.1QP

F or     a species to act as a Brønsted base, an atom in the species must possess a lone pair of electrons. Explain why this is so.

Interpretation Introduction

Interpretation: For a species to act as Bronsted base, an atom in the species must possess a lone pair of electrons has to be explained.

Concept Introduction: Bronsted's definition is based on the chemical reaction that occurs when both acids and bases are added with each other.  In Bronsted's theory acid donates proton, while base accepts proton from acid resulting in the formation of water.

Example: Consider the following reaction.

$\text{HCl}\text{+}{\text{NH}}_{\text{3}}\to {\text{NH}}_{\text{4}}{}^{\text{+}}\text{+}{\text{Cl}}^{\text{-}}$

Hydrogen chloride donates a proton, and hence it is a Bronsted acid. Ammonia accepts a proton, and hence it is a Bronsted base.

To Explain: why an atom in species must possess lone pair of electrons, for the species to act as Bronsted base.

Answer to Problem 16.1QP

Answer

The atom in a species must possess lone pair of electrons to act as Bronsted base because Bronsted base is ${\text{H}}^{\text{+}}$ acceptor.

Explanation of Solution

To explain Bronsted base

 Bronsted base is the one which can accept proton to form a conjugated acid.

To explain why lone pair is must

If a lone pair of electron is present, the species can accept proton.  This is because the Bronsted base accepts a proton to form conjugate acid.  Therefore lone pair of electron is must for a species to act as Bronsted base.

Conclusion

The necessity of presence of lone pair of electrons in an atom for a species to act as Bronsted base was explained.