How does the reactivity of alkali metals change within their group on the periodic table?

The reactivity of alkali metals increases as you move down the group on the periodic table due to the increasing atomic size and the decreasing ionization energy. As you go from lithium at the top of the group to cesium at the bottom, the outermost electron is located further from the nucleus. This greater distance means the attractive force between the nucleus and the outer electron becomes weaker, making it easier for the atom to lose that electron and participate in chemical reactions.

Additionally, as the atomic size increases, the shielding effect from the inner electrons also increases, which further reduces the effective nuclear charge experienced by the outermost electron. This combination of increased atomic size and reduced ionization energy results in greater reactivity, allowing alkali metals to react more vigorously with non-metals and water as one progresses down the group. This characteristic is crucial in predicting the behavior of these metals in chemical reactions.