The boiling points of halogen compounds are less easily rationalized. The number of electrons, their polarizability, and the number of nuclei all influence the boiling point. Seven halogenated organic compounds are listed in the following table. They all have similar numbers of electrons (62 to 72) and, except for bromine, similar molecular weights (130 to 142). However, the number of individual atoms that compose each molecule varies considerably.
The boiling points of these compounds also vary markedly, ranging from -78 º to 154 ºC. It is instructive to estimate the relative boiling point order from the structures given, by entering a number in the text box beneath each compound. As before, 1 is highest boiling & 7 is lowest boiling.