The relationship between the number of carbon atoms and boiling point is inversely proportional. In the alkane series of hydrocarbons, as the number of carbon atoms decreases, the normal boiling point of the compounds decreases. The reason behind this is that longer chains of molecules require more energy to separate the bonds while shorter chains or molecules with lower number of carbon atoms require less energy to break away from each other. Thus, low carbon molecules have lower boiling point.
