What defines an alkaline earth metal?

An alkaline earth metal is defined as an element that belongs to group 2 of the periodic table, characterized by having two electrons in their outermost shell. This electron configuration results in certain chemical properties, such as a tendency to lose those two electrons easily, forming cations with a +2 charge. This characteristic is fundamental to their reactivity and the types of compounds they form; for example, alkaline earth metals readily react with halogens to create salts.

The presence of two valence electrons also affects the alkaline earth metals' physical properties, such as melting and boiling points, which differ significantly from those of other groups on the periodic table. Furthermore, these metals tend to exhibit a more moderate level of reactivity compared to alkali metals, which have one electron in their outermost shell, leading to very different chemical behaviors and applications.

While other groups in the periodic table have distinctive configurations, the defining feature of alkaline earth metals specifically relates to that unique two-electron configuration.