What happens to the melting and boiling points of group 17 elements as one moves down the group?

As one moves down Group 17, also known as the halogens, the melting and boiling points increase. This trend can be attributed to the increase in molecular size and mass. As you progress down the group from fluorine to iodine, the number of electrons increases, leading to a greater extent of London dispersion forces, which are a type of van der Waals forces.

These intermolecular forces become stronger with larger atoms, as larger electron clouds are more polarizable. The strength of these forces directly correlates to the melting and boiling points; as the forces become stronger, more energy is required to overcome them, resulting in higher melting and boiling points for the halogen elements. For instance, fluorine and chlorine are gases or liquids at room temperature, whereas bromine is a liquid, and iodine is a solid, illustrating this increasing trend in physical state and temperature thresholds for phase changes.