Question

Consult your online resources for additional practice. Which of the following are Lewis bases? $$\begin{array}{c} \mathrm{Ag}^{+} \\ \mathrm{H}_{2} \mathrm{O} \\ \mathrm{NH}_{3} \end{array}$$ (A) I only (B) I and II only (C) II and III only (D) I, II, and III

Short answer

C

Step-by-step solution

Understanding Lewis Bases

A Lewis base is a species that can donate a pair of electrons. This usually means it has a lone pair of electrons.

Analyze \(\mathrm{Ag}^{+}\)

\(\mathrm{Ag}^{+}\) is a cation and lacks electrons to donate. Therefore, \(\mathrm{Ag}^{+}\) cannot be a Lewis base.

Analyze \(\mathrm{H}_{2} \, \mathrm{O}\)

\(\mathrm{H}_{2}\mathrm{O}\) has two lone pairs of electrons on the oxygen atom, which can be donated. Therefore, \(\mathrm{H}_{2}\mathrm{O}\) is a Lewis base.

Analyze \(\mathrm{NH}_{3}\)

\(\mathrm{NH}_{3}\) has a lone pair of electrons on the nitrogen atom, which can be donated. Therefore, \(\mathrm{NH}_{3}\) is a Lewis base.

Determine the Answer

Based on the analysis, \(\mathrm{H}_{2}\mathrm{O}\) and \(\mathrm{NH}_{3}\) are Lewis bases. The correct choice is (C) II and III only.

Key concepts

Electron Donation

To understand why \( \text{H}_{2}\text{O} \) and \( \text{NH}_{3} \) are Lewis bases, we should first delve into the idea of electron donation. Imagine you have extra candy to give out, and your friend doesn't have any. You would be the donor, your friend the recipient. Similarly, in chemistry, a Lewis base is a species that can donate a pair of electrons to a Lewis acid, which accepts those electrons. This process is fundamental in the formation of coordinate covalent bonds, where both bonding electrons come from the same atom—the donor. Understanding this concept helps us easily identify Lewis bases like \( \text{H}_{2}\text{O} \) and \( \text{NH}_{3} \), which have electrons ready for donation.

Lewis bases are critical in many chemical reactions and processes. They often interact with cations, helping to stabilize them by donating electrons, which is crucial in various analytical techniques.

Lone Pairs

Lone pairs are pivotal in identifying Lewis bases. They are pairs of valence electrons that are not involved in chemical bonding. Think of them as shy students in a classroom; they're present and ready to participate if needed. Molecules with lone pairs can donate these electrons to electrophilic (electron-loving) species.

For instance, in \( \text{H}_{2}\text{O} \), the oxygen atom has two lone pairs. These lone pairs make water a versatile and common Lewis base. Similarly, in \( \text{NH}_{3} \), the nitrogen atom has one lone pair. This lone pair is what allows ammonia to act as a Lewis base, readily donating electrons in various chemical reactions. Understanding the presence and role of lone pairs is essential for identifying and predicting the behavior of Lewis bases in chemistry.

Cation Analysis

Analyzing cations is crucial for determining Lewis bases. Cations, like \( \text{Ag}^{+} \), are positively charged species that lack electrons. Due to this electron deficiency, cations are generally not Lewis bases. Instead, they are often Lewis acids because they can accept electrons.

In the given problem, \( \text{Ag}^{+} \) cannot donate electrons as it is already positively charged and lacks the necessary electron pairs. This analysis helped us exclude \( \text{Ag}^{+} \) from being a Lewis base, leaving us with the two electron-rich species: \( \text{H}_{2}\text{O} \) and \( \text{NH}_{3} \). Recognizing the electron configuration and charge of species is key to understanding their roles in chemical reactions and their classification as either Lewis acids or bases.