why does iodine have a higher boiling point than chlorine?

If we look at group 7 of the periodic table, we can see that iodine is below chlorine. The trend in going down a group in the periodic table is that the number of electron shells increases, therefore, number of electrons increases. This means a molecule of iodine (I₂) has more electrons than a molecule of chlorine (Cl₂) so the van der waal's inter molecular forces are stronger and require more energy to overcome meaning the boiling point of iodine is higher than that of chlorine.