Which type of intermolecular force accounts for each of these differences? (b) Xe is a liquid at atmospheric pressure and 120 K, whereas Ar is a gas under the same conditions. (c) Kr, atomic weight 84 amu, boils at 120.9 K, whereas Cl₂, molecular weight about 71 amu, boils at 238 K.

Verified step by step guidance

1. Step 1: Understand that intermolecular forces are the forces of attraction between molecules. They are weaker than intramolecular forces, which are the forces within a molecule.
2. Step 2: Identify the types of intermolecular forces. They include London dispersion forces, dipole-dipole interactions, and hydrogen bonding.
3. Step 3: Recognize that both Xe (Xenon) and Ar (Argon) are noble gases, and they do not form molecules. Therefore, they do not have dipole-dipole interactions or hydrogen bonding. The only type of intermolecular force they can have is London dispersion forces.
4. Step 4: Understand that London dispersion forces are temporary attractive forces that result when the electrons in two adjacent atoms occupy positions that make the atoms form temporary dipoles. These forces are present in all molecules, whether they are polar or nonpolar.
5. Step 5: Note that the strength of London dispersion forces increases with the size and shape of the molecule or atom. In this case, Xe is larger than Ar, so it has stronger London dispersion forces. This is why Xe is a liquid at atmospheric pressure and 120 K, whereas Ar is a gas under the same conditions.

Key Concepts

Intermolecular Forces

Intermolecular forces are the attractive forces between molecules that influence their physical properties, such as boiling and melting points. These forces include hydrogen bonding, dipole-dipole interactions, and London dispersion forces. The strength and type of these forces determine whether a substance exists as a solid, liquid, or gas under specific conditions.

London Dispersion Forces

London dispersion forces are a type of van der Waals force that arise from temporary fluctuations in electron density within molecules, leading to instantaneous dipoles. These forces are present in all molecules, but they are particularly significant in nonpolar substances like noble gases. The strength of London dispersion forces increases with the size and polarizability of the atoms involved, which is crucial for understanding the behavior of xenon (Xe) compared to argon (Ar).

Phase Changes and Conditions

Phase changes refer to the transitions between solid, liquid, and gas states, which are influenced by temperature and pressure. At atmospheric pressure and 120 K, xenon (Xe) is a liquid due to stronger intermolecular forces compared to argon (Ar), which remains a gas. Understanding the conditions under which substances change phases is essential for predicting their states at given temperatures and pressures.