The reactivity of elements generally increases as you go down a group in the periodic table. This is because elements in the same group have the same number of valence electrons, and as you go down a group, the number of valence electrons increases. This causes the atoms to have a higher positive charge, which makes them more reactive because they are more likely to form chemical bonds with other atoms.
However, the reactivity of elements decreases as you go down group 7 (the halogens) in the periodic table. This is because the valence shell of these elements is already full, so they are less likely to form chemical bonds with other atoms. As a result, the atoms in group 7 are less reactive than those in other groups.