The boiling points of small molecules are significantly affected by the types of intermolecular forces present, as well as by the size and shape of the molecules.

The most critical factor influencing a molecule’s boiling point is the nature of the intermolecular forces that operate between the molecules. Intermolecular forces are the attractive forces that act between different molecules. There are three primary types of intermolecular forces: London dispersion forces, dipole-dipole interactions, and hydrogen bonding.

London Dispersion Forces:
These are the weakest form of intermolecular force and are present in all molecules, regardless of their polarity. The strength of London dispersion forces increases with the size and complexity of the molecule, meaning that larger molecules or those with more intricate shapes generally exhibit higher boiling points.

Dipole-Dipole Interactions:
These interactions occur between polar molecules, which possess a positive end and a negative end. Dipole-dipole interactions are stronger than London dispersion forces; therefore, polar molecules typically have higher boiling points compared to nonpolar molecules of similar size and shape.

Hydrogen Bonding:
This is the strongest type of intermolecular force, arising when a hydrogen atom is covalently bonded to a highly electronegative atom, such as nitrogen, oxygen, or fluorine. The hydrogen atom is then attracted to another electronegative atom. Molecules that can engage in hydrogen bonding tend to have significantly higher boiling points than comparable molecules that cannot form these bonds.

In addition to intermolecular forces, the size of the molecule also influences its boiling point. Larger molecules contain more electrons, which can enhance the strength of London dispersion forces, leading to increased boiling points.

Furthermore, the shape of the molecule can affect its boiling point. Molecules with more complex or elongated shapes have a greater surface area available for interaction with other molecules. This increased surface area can result in stronger London dispersion forces, contributing to higher boiling points.

In summary, the boiling point of a small molecule is determined by the types of intermolecular forces it can form, as well as its size and shape.