Refrigerators have a unit called a compressor that liquefies...

Refrigerators have a unit called a compressor that liquefies a gas. The refrigerator is cooled by a continuous cycle of compression of the gas to produce the liquid, followed by evaporation of the liquid to provide the cooling. Ammonia (NH $_{3}$ ) and sulfur dioxide $\left(\mathrm{SO}_{2}\right)$ were the gases used originally, and hexafluoroethane $\left(\mathrm{C}_{2} \mathrm{F}_{6}\right)$ has been used since the 1990 s. What are the intermolecular interactions that characterize these substances?

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Key Concepts

Hydrogen Bonding

Hydrogen bonding is a strong type of intermolecular force that occurs when a hydrogen atom, bonded to a highly electronegative atom like nitrogen, oxygen, or fluorine, interacts with a lone pair of electrons on a nearby electronegative atom. This interaction plays a significant role in determining the physical properties of substances that can form such bonds, for example by enabling higher boiling points.

Dipole-Dipole Interactions

Dipole-dipole interactions occur between molecules that have permanent dipole moments due to uneven distribution of electrons. These attractions, which are intermediate in strength, result from the alignment of positive and negative ends of polar molecules and are particularly important in substances with asymmetric molecular geometries.

London Dispersion Forces

London dispersion forces are weak intermolecular forces that arise from temporary fluctuations in electron clouds, leading to momentary dipoles even in nonpolar molecules. They are universally present in all molecular substances and become the dominant force in nonpolar molecules, affecting properties like boiling and melting points.

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