How do the boiling and melting points of alkynes change with increasing molecular structure?

As the molecular structure of alkynes increases, their boiling and melting points also increase. This trend can be attributed to the increasing molecular weight and surface area associated with larger alkynes. As the number of carbon atoms increases, there are more electrons and a larger molecular surface, which enhances the van der Waals forces (dispersion forces) between the molecules. These intermolecular forces must be overcome during the phase change from liquid to gas (boiling) or solid to liquid (melting). Therefore, larger alkynes require more energy to break these forces, resulting in higher melting and boiling points.

This behavior is consistent across hydrocarbons, where larger and more complex molecules generally exhibit higher boiling and melting points due to the increased strength of intermolecular interactions.