Explain the decrease in reactivity of Group 2 elements as you go down the periodic table

Group 2 elements are metals that all form cations in a chemical reaction. This means they lose their valence electrons to become positive (2+) ions. Their reactivity depends on how easily the atoms can lose these electrons. As you go down the periodic table, the elements have a larger number of electrons and larger nuclei. These electrons orbit the nucleus in shells and therefore the number of shells increases, leading to an overall increase in atomic radius. The valence electrons are further away from the nucleus and therefore experience less electrostatic attraction from the positive nucleus. The increased shielding by the higher number of electron shells also contributes to the decrease of this electrostatic attraction. These two factors override the fact that as mass number increases, the nucleus exerts a stronger nuclear attraction on its electrons. Therefore as you go down the group the valence electrons are more easily lost and the elements' ionisation energies decrease.