Problem 36 - Chemistry The Molecular Science

Question

The hybridization of the two nitrogen atoms differs in \(\mathrm{NH}_{4} \mathrm{NO}_{3}\) (a) Designate the correct hybridization for each nitrogen atom. (b) What is the approximate bond angle around each nitrogen?

Step-by-Step Solution

Answer

Ammonium nitrogen is \(\mathrm{sp}^3\) with 109.5° bond angles; nitrate nitrogen is \(\mathrm{sp}^2\) with 120° bond angles.

Step 1: Identify the Nitrogen Atoms

In the compound \(\mathrm{NH}_{4}\mathrm{NO}_{3}\), identify the two nitrogen atoms: the one in the ammonium ion (\(\mathrm{NH}_4^+\)) and the one in the nitrate ion (\(\mathrm{NO}_3^-\)).

Step 2: Determine Hybridization of Ammonium Nitrogen

For \(\mathrm{NH}_4^+\), the nitrogen is central and forms four sigma bonds with hydrogen atoms. Since there are no lone pairs on nitrogen, the hybridization is \(\mathrm{sp}^3\).

Step 3: Determine Bond Angle for Ammonium Nitrogen

In \(\mathrm{NH}_4^+\), due to \(\mathrm{sp}^3\) hybridization, the bond angle around the nitrogen atom is approximately \(109.5^\circ\).

Step 4: Determine Hybridization of Nitrate Nitrogen

For \(\mathrm{NO}_3^-\), nitrogen is bonded to three oxygen atoms and has no lone pair. It forms one double bond, which indicates \(\mathrm{sp}^2\) hybridization due to the trigonal planar shape.

Step 5: Determine Bond Angle for Nitrate Nitrogen

In \(\mathrm{NO}_3^-\), due to \(\mathrm{sp}^2\) hybridization, the bond angle around the nitrogen atom is approximately \(120^\circ\).

Key Concepts

Nitrogen hybridization

The concept of hybridization in chemistry helps us understand how atoms bond in different molecules or polyatomic ions. Let's look at the compound \(\mathrm{NH}_4\mathrm{NO}_3\) to determine the hybridization states of its nitrogen atoms. The hybridization of an atom is determined by the number and arrangement of bonds it forms.

In \(\mathrm{NH}_4^+\) (ammonium ion), the nitrogen atom is the central atom bonded to four hydrogen atoms. Here, nitrogen forms four sigma bonds, and since it doesn't have any lone electron pairs, the hybridization is \(\mathrm{sp}^3\). This results in a tetrahedral shape around the nitrogen atom with an ideal bond angle of approximately \(109.5^\circ\).

Meanwhile, for \(\mathrm{NO}_3^-\) (nitrate ion), the nitrogen atom forms three bonds with oxygen atoms and again, it lacks lone pairs. One of these is a double bond, common in systems with \(\mathrm{sp}^2\) hybridization. This gives the nitrate nitrogen a planar trigonal shape with a bond angle close to \(120^\circ\).

Understanding these hybridization states helps predict both the shapes of molecules and the types of chemical bonding that occur between atoms.

Chemical bonding

Chemical bonding is the force that holds atoms together within a compound. In \(\mathrm{NH}_4\mathrm{NO}_3\), different types of bonds are present due to the nitrogen atoms found in both ammonium and nitrate ions.

In \(\mathrm{NH}_4^+\), nitrogen achieves bonding through \(\mathrm{sp}^3\) hybridization, forming sigma bonds with hydrogen atoms. Each hydrogen atom shares its electron with nitrogen, creating four single covalent bonds. These sigma bonds are the axis of direct overlap between the nitrogen's hybrid orbitals and each hydrogen's 1s orbital.

For \(\mathrm{NO}_3^-\), nitrogen uses \(\mathrm{sp}^2\) hybridization, bonding with oxygen atoms. Here, we observe a mix of sigma and pi bonds. The nitrogen atom forms sigma bonds with two oxygen atoms and a double bond with one oxygen atom, involving both a sigma bond and a pi bond. Pi bonds arise from the sideways overlap of p orbitals, adding extra bonding strength to certain pairs of atoms.

Different hybridization reflects how atoms use their electrons in making chemical bonds, revealing the versatile ways molecules can form and stabilize.

Molecular geometry

Molecular geometry explores the spatial arrangement of atoms around a central atom within a molecule. This geometry greatly influences the molecular properties like polarity, reactivity, and phase of matter.

In \(\mathrm{NH}_4^+\), the central nitrogen atom adopts \(\mathrm{sp}^3\) hybridization, leading to a tetrahedral molecular geometry. Tetrahedral arrangements have four corners with 109.5-degree angles between each bond, allowing for uniform distribution of electrons and reducing electron pair repulsions.

Conversely, in \(\mathrm{NO}_3^-\), nitrogen's \(\mathrm{sp}^2\) hybridization results in a trigonal planar geometry. The arrangement ensures atoms are spaced \(120^\circ\) apart, forming a flat plane. This optimizes electron density distribution around the nitrogen, contributing to the overall stability of the ion.

The geometry of molecules supports the understanding of molecular interactions and potential applications, playing a crucial role in fields such as material science, pharmacology, and environmental chemistry.