How does the size of hydrocarbon molecules affect their boiling points?

The relationship between the size of hydrocarbon molecules and their boiling points is fundamentally linked to the intermolecular forces present in the substance. As the size of hydrocarbon molecules increases, so does the surface area. Larger molecules have more electrons and an increased surface area, which leads to stronger London dispersion forces (a type of van der Waals force) between the molecules.

Hence, as hydrocarbon chains become longer and more complex, the energy required to overcome these intermolecular attractions also increases, resulting in higher boiling points. This trend is particularly evident when comparing straight-chain hydrocarbons, where an increase in molecular size typically correlates with an increase in boiling point due to enhanced dispersion forces.

The other potential answers do not accurately describe this trend. Smaller molecules cannot possess higher boiling points than larger ones because they would have weaker intermolecular interactions. Saying there’s no relationship overlooks the clear connection between molecular size and boiling point, and attributing boiling points solely to molecular weight disregards the influence of molecular structure and intermolecular forces. Thus, the correct explanation of boiling points in hydrocarbons as the size increases is that they generally increase due to stronger intermolecular forces.