Why does chemical reactivity increase from top to bottom in groups 1A and 2A?

As you move down groups 1A and 2A in the periodic table, atomic size increases due to the addition of electron shells. This increase in size leads to a greater distance between the nucleus and the outermost electrons, which reduces the effective nuclear charge felt by these electrons. Consequently, the outer electrons are more easily lost, enhancing reactivity.

Ionization energy is the energy required to remove an electron from an atom. In groups 1A and 2A, ionization energy decreases as you move down the group because the outer electrons are further from the nucleus and experience more shielding from inner electrons. Lower ionization energy means that these elements can lose their outermost electrons more readily, increasing their reactivity.

The elements in groups 1A (alkali metals) and 2A (alkaline earth metals) are characterized by their tendency to lose one or two electrons, respectively, to achieve a stable electron configuration. As reactivity is defined by the ability to lose these electrons, the increased atomic size and decreased ionization energy down the groups lead to higher reactivity, making these metals more reactive as you descend the groups.