2 Group 17 elements are commonly referred to as the halogens.(a) State and explain the trend in volatility of chlorine, bromine and iodine down the group........................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................................... [3]

(a) The volatility of Group 17 elements (halogens) decreases down the group from chlorine to iodine.

This trend can be explained by the increase in molecular size and the strength of the van der Waals forces.

1. Increase in Molecular Size: As we move down the group, the number of electron shells increases, leading to an increase in the size of the atoms. For example, iodine atoms are larger than bromine atoms, which are in turn larger than chlorine atoms.

2. Strength of Van der Waals Forces: The larger the size of the atom, the stronger the van der Waals forces between the molecules. This is because larger atoms have more electrons, leading to greater temporary dipoles and thus stronger temporary attractions.

Therefore, as we move down the group from chlorine to bromine to iodine, the increasing molecular size and strength of the van der Waals forces make it more difficult for the molecules to break free from each other and become a gas. This results in a decrease in volatility.