What primarily distinguishes alkali metals from alkali earth metals?

Alkali metals are primarily distinguished from alkaline earth metals by their tendency to lose one electron to form positive ions. Alkali metals, which belong to Group 1 of the periodic table, have a single valence electron. When they react, they readily lose this one electron to achieve a stable electron configuration, typically forming cations with a +1 charge.

In contrast, alkaline earth metals, located in Group 2, have two valence electrons and generally lose both to form cations with a +2 charge. This distinction in the number of valence electrons and the resultant charge of the ions they form is fundamental to understanding their reactivity and properties. The reactivity of alkali metals is also influenced by their need to lose just one electron compared to the two required for alkaline earth metals. This makes alkali metals generally more reactive than their alkaline earth counterparts.