Describe the trend in relative molecular mass down Group 7.

In Group 7 of the periodic table, known as the halogens, there is a clear trend in relative molecular mass as you move down the group. The relative molecular mass increases from fluorine (F2) at 38 g/mol to chlorine (Cl2) at 71 g/mol, then to bromine (Br2) at 160 g/mol, and finally to iodine (I2) at 254 g/mol. This increase is due to the addition of more protons and neutrons in the nuclei of the halogen atoms, resulting in heavier molecules. Understanding this trend helps predict the physical properties and reactivity of halogens.