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) \(\mathrm{dsp}^{2}\)

Short answer

The hybridization state of the central atom in the conjugate base \\(\mathrm{NH}_{3}\\) is \\(\mathrm{sp}^{3}\\).

Step-by-step solution

Identify the structure of the molecular ion

The molecular ion in question is \(\mathrm{NH}_{4}^{+}\). It is an ammonium ion with four hydrogen atoms bonded to a central nitrogen atom in a tetrahedral geometry. The nitrogen atom typically exhibits an \(sp^{3}\) hybridization to accommodate these bonds.

Determine the conjugate base

To find the conjugate base of \(\mathrm{NH}_{4}^{+}\), remove one hydrogen proton (H extsuperscript{+}). This gives us \(\mathrm{NH}_{3}\), which is ammonia.

Analyze the hybridization of the central atom in \\(\mathrm{NH}_{3}\\)

Ammonia, \(\mathrm{NH}_{3}\), consists of one nitrogen atom bonded to three hydrogen atoms. It has a lone pair of electrons and exhibits a trigonal pyramidal shape.

Determine the hybridization of nitrogen in \\(\mathrm{NH}_{3}\\)

The nitrogen atom in \(\mathrm{NH}_{3}\) uses \(\mathrm{sp}^{3}\) hybrid orbitals to form bonds with hydrogen atoms and maintain its lone pair. This results in a trigonal pyramidal shape due to one non-bonding electron pair.

Key concepts

Ammonium Ion

The ammonium ion, represented as \( \mathrm{NH}_{4}^{+} \), is a positively charged ion formed when an ammonia molecule, \( \mathrm{NH}_{3} \), gains a proton. This results in a structure where four hydrogen atoms are symmetrically bonded to a central nitrogen atom. The geometry of this arrangement is tetrahedral, a common shape that helps minimize repulsion between the hydrogen atoms. To accommodate this shape, the nitrogen atom undergoes \( \mathrm{sp}^{3} \) hybridization. This means that one 's' orbital and three 'p' orbitals of nitrogen mix to form four equivalent \( \mathrm{sp}^{3} \) hybrid orbitals. These orbitals allow for the formation of \( \sigma \) bonds with each hydrogen atom, providing a stable structure. The presence of the positive charge arises because a lone pair of electrons initially located at nitrogen is used to form the additional bond with the fourth hydrogen atom.

Ammonia

Ammonia, or \( \mathrm{NH}_{3} \), is a simple molecule where a nitrogen atom is bonded to three hydrogen atoms. Unlike the ammonium ion, ammonia has a lone pair of electrons on the nitrogen. This lone electron pair significantly influences the geometry and hybridization of ammonia.Nitrogen in ammonia exhibits \( \mathrm{sp}^{3} \) hybridization, similar to the structure seen in the ammonium ion. Here, three of the \( \mathrm{sp}^{3} \) hybrid orbitals are used to form bonds with the hydrogen atoms, while the fourth contains the lone pair of electrons. This spatial arrangement isn't entirely symmetrical due to the lone pair, which occupies more space and pushes the hydrogen atoms slightly closer. The result is a molecular shape known as trigonal pyramidal. This shape is critical to understanding ammonia's physical and chemical properties, including its higher solubility in water and ability to act as a weak base, by accepting a proton to revert back to the ammonium ion.

Trigonal Pyramidal

The trigonal pyramidal geometry is a three-dimensional shape seen in molecules like ammonia. In a trigonal pyramidal structure, a central atom is bonded to three other atoms and has one lone pair of electrons. This geometry is distinct from a simple trigonal planar shape due to the presence of the lone pair occupying one of the four tetrahedrally oriented hybrid orbitals. Key features of the trigonal pyramidal geometry include:

• Three bonded pairs of electrons forming bonds with surrounding atoms.
• A lone pair of electrons that occupies more space than a bonding pair, causing a bond angle that is less than the typical 109.5° seen in a perfect tetrahedron, often around 107° in the case of ammonia.
• Resulting shape appears like a pyramid with the apex being the central atom, while the base is formed by the three bonded atoms.

Understanding this geometry is crucial, as the lone pair significantly influences molecular interactions and can contribute to the molecule's polarity, also affecting its physical and chemical behavior in different environments.