Question

Which of the following molecules has the shortest nitrogen-to-nitrogen bond: \(\mathrm{N}_{2} \mathrm{H}_{4}, \mathrm{~N}_{2} \mathrm{O}, \mathrm{N}_{2}, \mathrm{~N}_{2} \mathrm{O}_{4} ?\) Explain.

Short answer

\(\mathrm{N}_{2}\) has the shortest nitrogen-to-nitrogen bond due to its triple bond.

Step-by-step solution

Identify the Types of Nitrogen-Nitrogen Bonds

Let's look at each molecule:- \( \mathrm{N}_2\) has a triple bond between the two nitrogen atoms.- \( \mathrm{N}_2 \mathrm{H}_4\) has a single bond between the two nitrogen atoms.- \( \mathrm{N}_2 \mathrm{O}\) involves a nitrogen-nitrogen double bond in one of its resonance structures.- \( \mathrm{N}_2 \mathrm{O}_4\) generally contains nitrogen atoms connected by a single bond.

Compare Bond Orders

The bond order refers to the number of chemical bonds between a pair of atoms. A higher bond order typically means a stronger and shorter bond:- In \( \mathrm{N}_2\), there is a triple bond with a bond order of 3.- In \( \mathrm{N}_2 \mathrm{H}_4\) and \( \mathrm{N}_2 \mathrm{O}_4 \), there is a single bond with a bond order of 1.- In \( \mathrm{N}_2 \mathrm{O}\), the nitrogen-nitrogen bond is generally a double bond with a bond order of 2.

Determine the Shortest Bond

Among the different types of nitrogen bonds, triple bonds are shorter than double and single bonds due to their higher bond order. Since \( \mathrm{N}_2\) is the only molecule with a nitrogen-nitrogen triple bond, it will have the shortest nitrogen-nitrogen bond.

Key concepts

Bond Order

Bond order is a term used to describe the number of chemical bonds between a pair of atoms. It gives us a sense of the stability and strength of a bond within a molecule. Generally, a higher bond order means a stronger and shorter bond. The bond order is represented by the number of electrons shared between the atoms. More electrons mean more attraction, which pulls the atoms closer together.
An easy way to think about bond order is to imagine it as a scale of single, double, and triple bonds.

• A single bond often has a bond order of 1, which corresponds to two atoms sharing one pair of electrons.
• A double bond has a bond order of 2, meaning two pairs of electrons are shared.
• A triple bond has a bond order of 3, implying three pairs of electrons are shared.

Understanding bond order is crucial for predicting the length and strength of bonds in various molecules.

Triple Bond

Triple bonds are one of the strongest and shortest types of covalent bonds. They involve the sharing of three pairs of electrons between two atoms. Because of this high level of electron sharing, triple bonds have a bond order of 3. The triple bond in nitrogen molecules, represented by \( \mathrm{N_2} \), is an excellent example. This molecule is made up of two nitrogen atoms connected by a triple bond, making it incredibly strong.
Triple bonds are shorter than both single and double bonds.

• This is due to the greater attraction between the nuclei of the bonded atoms, pulling them closer.
• In molecules like \( \mathrm{N_2} \), this results in a considerably shorter bond length, which imparts great stability to the molecule.

Understanding triple bonds helps explain why they are generally found in very stable molecules.

Double Bond

Double bonds occur when two atoms share two pairs of electrons. This type of bond has a bond order of 2. Double bonds are stronger and shorter than single bonds, but not as strong or short as triple bonds.
An example of a double bond in a nitrogen-containing molecule is found in the resonance structures of \( \mathrm{N_2O} \). Here, at least one of the nitrogen-nitrogen bonds is double in character.
Double bonds are:

• Commonly associated with unsaturation in organic molecules. This unsaturation creates regions of higher electron density, thus stronger interactions.
• More flexible than triple bonds, allowing for additional chemical reactivity, such as undergoing reactions to form rings or more complex structures.

By understanding double bonds, you can see why they play a key role in the function and reactivity of life’s essential molecules.

Single Bond

Single bonds are the simplest and weakest type of chemical bond between two atoms. They involve the sharing of one pair of valence electrons, resulting in a bond order of 1.
Single bonds are typically found in most organic structures, such as \( \mathrm{N_2H_4} \) and \( \mathrm{N_2O_4} \), where the nitrogen atoms share only one pair of electrons.
While single bonds are longer and weaker than double and triple bonds, they are crucial for the structure of many molecules due to their flexibility.

• They allow for rotation around the bond axis, which can lead to different molecular shapes and interactions.
• This rotational flexibility is important in large biological molecules like proteins and DNA.

Single bonds are foundational in understanding how molecules maintain their structure and interact with each other in diverse chemical environments.