Problem 51 - A Complete Resource Book in Chemistry for JEE Main

Question

What is the hybridization state of the central atom in the conjugate base of \(\mathrm{NH}_{4}^{+}\)ion? (a) sp (b) \(\mathrm{sp}^{3}\) (c) \(\mathrm{sp}^{3}\) (d) \(\mathrm{dsp}^{2}\)

Step-by-Step Solution

Answer

The hybridization state of the central atom in the conjugate base of \\(\mathrm{NH}_{4}^{+}\\) is \\(\mathrm{sp}^{3}\\), so the answer is both (b) and (c).

Step 1: Understanding the Conjugate Base

The first step is to identify the conjugate base of the given cation, which is \(\mathrm{NH}_{4}^{+}\). A conjugate base is formed by removing one proton (H\(^+\)) from the compound. Therefore, the conjugate base of \(\mathrm{NH}_{4}^{+}\) is \(\mathrm{NH}_{3}\).

Step 2: Determine Hybridization of NH₃

Next, we analyze the hybridization state of the central atom in \(\mathrm{NH}_{3}\), the conjugate base. Ammonia, \(\mathrm{NH}_{3}\), has a nitrogen atom at the center surrounded by three hydrogen atoms and one lone pair of electrons. This configuration involves four regions of electron density (three bonds and one lone pair).

Step 3: Verifying Hybridization as sp³

In molecular geometry, an atom with four regions of electron density, such as in \(\mathrm{NH}_3\), adopts \(\mathrm{sp}^3\) hybridization. This means the nitrogen in \(\mathrm{NH}_3\) mixes one s orbital and three p orbitals to form four equivalent \(\mathrm{sp}^3\) hybrid orbitals.

Step 4: Selecting the Correct Answer

Finally, from our analysis, the central atom nitrogen in \(\mathrm{NH}_3\) exhibits \(\mathrm{sp}^3\) hybridization. Checking the options given, the correct choice is (b) \(\mathrm{sp}^{3}\). The answer (c) is visually identical to (b), likely indicating a typographical error in the options, thus making both correct.

Key Concepts

Conjugate Base

When we talk about conjugate bases in chemistry, we're referring to the species that remains after a proton (H\(^+\)) is removed from an acid. This concept is part of the Brønsted-Lowry acid-base theory. In this context, if we consider the ammonium ion, \(\mathrm{NH}_{4}^{+}\), as the acid, removing one proton gives us the conjugate base, ammonia, or \(\mathrm{NH}_{3}\). By understanding conjugate bases, students can grasp an important aspect of acid-base reactions. This process of losing a proton is fundamental in predicting how molecules will interact in different chemical environments.

NH4+ Ion

The \(\mathrm{NH}_{4}^{+}\) ion, commonly known as the ammonium ion, is a pivotal molecule in chemistry. It comprises a nitrogen atom bonded to four hydrogen atoms, resulting in a positive charge overall. The structure of ammonium ion is highly symmetrical, with a geometry that reflects tetrahedral characteristics due to the equal bond angles around the central nitrogen atom.

• This geometric shape is significant because it provides insight into its bonding and reactivity.
• In solutions, \(\mathrm{NH}_{4}^{+}\) is a common representation of a weak acid, able to donate protons to become \(\mathrm{NH}_{3}\).

This ability to donate protons showcases the dynamic nature of ammonium in various chemical reactions.

sp3 Hybridization

Hybridization is a central concept in the explanation of molecular shapes and bonding. For \(\mathrm{NH}_{3}\), the nitrogen atom undergoes \(\mathrm{sp}^3\) hybridization. This means it blends one s orbital and three p orbitals from its electron shell to form four equivalent hybrid orbitals.These \(\mathrm{sp}^3\) hybrid orbitals are crucial, as they arrange themselves to minimize electron repulsion, resulting in a geometry that supports bonding with hydrogen atoms.

• The use of \(\mathrm{sp}^3\) hybridization for the nitrogen atom enables the formation of stable, directional bonds.
• This arrangement also explains why \(\mathrm{NH}_{3}\) is a trigonal pyramidal molecule, with three bonds and one lone pair.

Understanding \(\mathrm{sp}^3\) hybridization helps in predicting and rationalizing the structure and properties of amines.

Molecular Geometry

Molecular geometry is a term reflecting the spatial arrangement of atoms in a molecule. It is crucial because it influences physical and chemical properties like polarity, reactivity, and color.In the case of \(\mathrm{NH}_{3}\), the hybridization of nitrogen into \(\mathrm{sp}^3\) orbitals leads to what is known as trigonal pyramidal geometry.

• This pyramidal shape arises due to the three hydrogen atoms and one lone pair of electrons repelling each other within the framework.
• The lone pair occupies more space than the hydrogen bonds, distorting the geometry slightly but markedly.

Understanding molecular geometry provides key insights into how molecules interact and form compounds. Grasping these spatial concepts is essential for predicting molecular behavior in chemical reactions.