Why do longer chain alkanes have higher boiling points?

Longer chain alkanes have higher boiling points because they have more points of contact, leading to stronger intermolecular forces.

In more detail, alkanes are hydrocarbons, which are compounds made up of hydrogen and carbon atoms. The carbon atoms in alkanes are linked together in a chain, and the length of this chain can vary. The longer the chain, the more carbon atoms there are, and therefore, the more points of contact there are between the molecules.

These points of contact are where the intermolecular forces, specifically the van der Waals forces, act. Van der Waals forces are weak forces of attraction that exist between all molecules, whether they are polar or non-polar. They arise from the fluctuations in the electron distribution within molecules, which create temporary dipoles. These temporary dipoles induce dipoles in neighbouring molecules, leading to an attraction between them.

The strength of the van der Waals forces depends on the number of points of contact between the molecules. The more points of contact there are, the stronger the forces. This is why longer chain alkanes, which have more points of contact, have stronger van der Waals forces.

The boiling point of a substance is the temperature at which it changes from a liquid to a gas. This change of state requires energy to overcome the intermolecular forces holding the molecules together. Therefore, substances with stronger intermolecular forces have higher boiling points because more energy is needed to overcome these forces. This explains why longer chain alkanes, which have stronger van der Waals forces due to their greater number of points of contact, have higher boiling points.