Which gas would you expect to deviate most from ideal behavior under conditions of low temperature: F2, Cl2, or Br2? Explain.

The term 'intermolecular forces' (IMFs) refers to the various forces of attraction and repulsion that act between molecules. There are several types of IMFs, including hydrogen bonding, dipole-dipole forces, and London dispersion forces.
Understanding IMFs is crucial when predicting the behavior of gases under different conditions. For gases to display ideal behavior, as described by the ideal gas law, we assume that IMFs are nonexistent. However, in reality, all atoms and molecules exert some influence on one another, and it is these intermolecular forces that can cause real gases to deviate from ideal behavior.
When temperatures drop or pressures increase, the molecules are brought closer together, intensifying these forces. This interaction disrupts the free movement of the molecules, thereby affecting the gas properties that are described by the ideal gas law. A gas that has significant intermolecular forces will not obey the ideal gas equation as accurately as a gas with weaker IMFs.

Molecular polarizability describes how easily a molecule's electron cloud is distorted by an external electric field. This attribute is significant because it influences a molecule’s ability to induce dipoles in itself or in neighboring molecules, which strengthens intermolecular forces.
Larger molecules typically have more electron clouds, making them more polarizable. When discussing gases, polarizability is what gives rise to temporary dipole moments. These temporary dipoles result in an attraction between otherwise nonpolar molecules, which can lead to deviations from ideal gas behavior.
Polarizability increases down a group on the periodic table as atoms become larger due to the greater number of electron shells. This factor can help predict which gases are more likely to deviate significantly from ideal behavior, especially at low temperatures where the induced dipoles are more likely to influence the behavior of the gas.

Among the different intermolecular forces, London dispersion forces are the weakest but are also present in all molecules, whether polar or nonpolar. They are a type of force that is temporarily created due to momentary fluctuations in the electron density of a molecule, leading to a temporary dipole that induces a dipole in a neighboring molecule.
These forces are significant in molecules with large, easily polarizable electron clouds because they are more likely to experience fluctuations that lead to temporary dipoles. Hence, larger atoms or molecules, such as Br2 in the given exercise, generally have stronger London dispersion forces.
These temporary forces become more pronounced at lower temperatures because the decreased kinetic energy allows the molecules to interact more closely and frequently. A gas with strong London dispersion forces, like Br2, will deviate more from ideal behavior than a gas with weaker London dispersion forces, under conditions of low temperature.