Small Sentence: Alkali metals are more reactive than alkaline earth metals due to their lower ionization energies.
Big Sentence: The chemical reactivities of alkali metals are generally higher than those of alkaline earth metals, primarily because alkali metals, with their single valence electron, have lower ionization energies and can readily lose that electron to form positive ions, whereas alkaline earth metals have two valence electrons and require more energy to remove one, making them relatively less reactive.