text: Reactivity of Group I (Alkali metals) increases down the group. It has nothing to do with how much you are using so even if you add 0.1g of potassium and 1g of lithium to cold water, potassium being more reactive than lithium will react more violently than lithium.\nIt has to do with the electronic configuration. Group I metals tend to give away their 1 valence electron to attain stability with full octet (or duplet for lithium). As you go further down the Group, the atoms get bigger (more shells) and the valence electron gets further away from the attractive force of the nucleus (nucleus contains positively charged protons and neutral neutrons hence nucleus are overall, positively charged. Electrons are negatively charged hence there is a force of attraction between the nucleus and the electrons). Hence it becomes easier for the atom to lose that valence electron to form a stable configuration and the ease of giving away that valence electron translates to mean more reactive and finally, more violent, vigorously, explosively reaction down the group of alkali metals.\n\nHope this helps :)