Question

Which of the following clusters would you expect to be most strongly bound? 1\. \(\mathrm{NO} \cdots \mathrm{Ar}\) 2\. \(\mathrm{Ar} \cdots \mathrm{Ar}\) 3\. \(\mathrm{CCl}_4 \cdots \mathrm{Ar}\) 4\. \(\mathrm{HCl} \cdots \mathrm{Ar}\)

Short answer

Based on the analysis of intermolecular forces, the HCl...Ar cluster (option 4) is expected to be the most strongly bound due to the presence of both London dispersion forces and dipole-induced dipole interactions. The other clusters primarily rely on weaker London dispersion forces, resulting in less strong binding.

Step-by-step solution

Identify the intermolecular forces in each cluster

In order to compare the bonding strength in each cluster, we need to identify the main intermolecular forces present in each case: 1. In the NO...Ar cluster, the primary intermolecular interaction is a van der Waals force (London dispersion force) between the Ar atom and the polar NO molecule. 2. The Ar...Ar cluster is also held together by van der Waals forces, specifically London dispersion forces, which result from the fluctuations in the electron distribution around the noble gas atoms. 3. In the CCl4...Ar cluster, the primary force of attraction is a van der Waals force (London dispersion force) between the nonpolar CCl4 molecule and the Ar atom. 4. The HCl...Ar cluster experiences both van der Waals forces (London dispersion forces) and a weak dipole-induced dipole interaction due to the polar HCl molecule and the nonpolar Ar atom.

Compare the strengths of the intermolecular forces

Now that we have identified the intermolecular forces in each cluster, we can compare their strengths to determine which cluster is the most strongly bound: 1. The interaction between NO and Ar is relatively weak due to the London dispersion forces. NO is a polar molecule; nonetheless, the interaction with the nonpolar Ar atom is limited. 2. The Ar...Ar cluster has a relatively weak bond as well, as London dispersion forces are generally weaker than other types of intermolecular forces. 3. The CCl4...Ar cluster might be slightly stronger than the NO...Ar and Ar...Ar clusters due to the larger size of the CCl4 molecule, which can result in stronger London dispersion forces. 4. The HCl...Ar cluster benefits not only from the London dispersion forces but also from dipole-induced dipole interactions between the polar HCl molecule and the nonpolar Ar atom. This additional type of interaction, although still weak, contributes to stronger binding in the HCl...Ar cluster compared to the other clusters.

Identify the most strongly bound cluster

Based on the analysis of the intermolecular forces present in the given clusters, we can conclude that the HCl...Ar cluster (option 4) should be the most strongly bound due to the presence of both London dispersion forces and dipole-induced dipole interactions. The other clusters are primarily held together by weaker London dispersion forces only, which results in less strong binding.

Key concepts

Intermolecular Forces

Understanding intermolecular forces is crucial for grasping how molecules interact with each other. These forces are the attractive or repulsive forces that occur between neighboring particles, such as atoms, ions, or molecules. They are significantly weaker than intramolecular forces – the forces which keep a molecule intact.

For example, in the textbook exercise, we compare the strength of intermolecular interactions in different clusters of atoms and molecules. Intermolecular forces include hydrogen bonds, dipole-dipole interactions, ion-dipole interactions, and dispersion forces, each varying in strength and occurring under different circumstances.

The type and strength of these forces determine the physical properties of substances, such as boiling points, melting points, and solubility. In any given cluster, understanding which intermolecular forces are at play is fundamental for predicting its properties and stability.

London Dispersion Forces

Among the various intermolecular forces, London dispersion forces are considered the weakest. These forces are also known as induced dipole-induced dipole interactions. They arise from temporary fluctuations in the electron distributions within atoms or molecules. This temporary dipole can induce a dipole in an adjacent atom or molecule, leading to attraction.

Characteristics Influencing London Dispersion Forces

• The size of the atoms or molecules: Larger atoms or molecules with more electrons have stronger London dispersion forces.
• The shape of the molecule: More elongated molecules have larger areas to induce dipoles on neighboring molecules, making these interactions stronger.
• The number of atoms or molecules: A higher number of interacting particles increases the overall strength of dispersion forces within a substance.

For instance, in the CCl4...Ar cluster in the exercise, the relatively large size of the CCl4 molecule allows for a larger temporary dipole, thus slightly stronger London dispersion forces compared to those in the Ar...Ar cluster.

Dipole-Induced Dipole Interactions

Dipole-induced dipole interactions occur when a molecule with a permanent dipole induces a temporary dipole in a neighboring nonpolar molecule or atom. This type of interaction is stronger than the London dispersion force but still weaker than other intermolecular forces such as hydrogen bonding or pure dipole-dipole interactions.

Factors Affecting Dipole-Induced Dipole Interactions

• The strength of the permanent dipole in the polar molecule.
• The polarizability of the nonpolar particle or molecule, which is its ability to form a temporary dipole in the presence of a permanent dipole.
• The distance between the polar and nonpolar particles, as the strength of the interaction decreases with increased distance.

In the textbook exercise, the HCl...Ar cluster represents this interaction. The permanent dipole of the HCl molecule can induce a dipole in the Ar atom, leading to a relatively stronger binding compared to clusters only influenced by London dispersion forces.