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 \(\mathrm{NH}_3\) is \(\mathrm{sp}^3\).

Step 1: Determine the Conjugate Base

The conjugate base of the ammonium ion \(\mathrm{NH}_4^+\) is the species formed after the donation of a proton (\(\mathrm{H}^+\)). When \(\mathrm{NH}_4^+\) loses a proton, it becomes \(\mathrm{NH}_3\) (ammonia).

Step 2: Analyze the Central Atom's Geometry

The central atom in \(\mathrm{NH}_3\) is nitrogen. In \(\mathrm{NH}_3\), three hydrogen atoms are bonded to nitrogen, and there is one lone pair of electrons on the nitrogen. This makes the geometry a trigonal pyramidal shape.

Step 3: Determine the Hybridization

The trigonal pyramidal geometry in \(\mathrm{NH}_3\) suggests that the nitrogen uses \(\mathrm{sp}^3\) hybrid orbitals to form bonds. This hybridization involves one \(\mathrm{s}\) orbital and three \(\mathrm{p}\) orbitals combining to form four equivalent \(\mathrm{sp}^3\) hybrid orbitals.

Key Concepts

Conjugate Base

A conjugate base is the result of losing a proton (\(H^+\!\)) from an acid. In this context, the acid in question is the ammonium ion \(NH_4^+\!\), which is quite common in chemistry. When an acid donates a proton, the species that remains is known as its conjugate base. For the ammonium ion \(NH_4^+\!\), the loss of a proton directly forms ammonia, represented chemically as \(NH_3\!\).

• The key change here is the removal of one hydrogen ion (proton), shifting the atom's balance and forming a neutral \(NH_3\!\) molecule.
• This process transforms the positively charged ammonium ion into a neutral ammonia molecule.

Understanding conjugate bases is essential in acid-base chemistry, as it helps in predicting how substances will behave in different chemical reactions and environments. This change not only impacts the molecule's charge but also its geometry and electronic configuration.

Ammonium Ion

The ammonium ion is a positively charged, polyatomic ion with the formula \(NH_4^+\!\). It plays a crucial role in many biological and chemical systems. It is the product of ammonia accepting a proton.

• This ion is commonly found in nature, mainly in soil, fertilizers, and as a vital component in the nitrogen cycle.
• Chemically, \(NH_4^+\!\) is formed by the protonation of ammonia \(NH_3\!\).
• The addition of the proton leads to a tetrahedral geometry where the nitrogen is surrounded by four hydrogen atoms.

The ammonium ion's formation involves the \(sp^3\!\) hybridization of nitrogen, where one \(s\!\) orbital and three \(p\!\) orbitals mix to form four equivalent \(sp^3\!\) hybrid orbitals. Its stable structure and formation are critical for processes like cation exchange in soils, influencing nutrient availability.

Trigonal Pyramidal Geometry

Trigonal pyramidal geometry is a common geometrical arrangement observed in certain molecular structures where a central atom is connected to three peripheral atoms, with one lone pair of electrons occupying one of the positions that would make up a tetrahedral geometry. In the case of \(NH_3\!\), or ammonia, the nitrogen atom is in the center, with three hydrogen atoms surrounding it.

• The presence of a lone pair of electrons on nitrogen pushes the hydrogen atoms closer together.
• This lone pair creates a repulsion that alters the bond angles, reducing them from the ideal tetrahedral angle of 109.5° to about 107°.
• Thus, ammonia takes on a trigonal pyramidal shape rather than a perfect tetrahedral shape.

Trigonal pyramidal geometry not only affects the shape but also the reactivity and polarity of the molecule. For instance, the shape contributes to ammonia being a polar molecule, which impacts its intermolecular interactions and solubility in water. Understanding this geometry is vital for predicting molecule behavior in chemical reactions and interactions.