What is the primary cause of alkaline earth metals' reactivity?

The reactivity of alkaline earth metals is primarily attributed to their low ionization energy. These elements, which include beryllium, magnesium, calcium, strontium, barium, and radium, have two electrons in their outermost shell. To achieve a stable electron configuration, they need to lose these two valence electrons.

Low ionization energy means that less energy is required to remove these outer electrons, facilitating the metal's ability to readily react with other elements or compounds. Consequently, alkaline earth metals are more likely to participate in chemical reactions, often forming positive ions. This characteristic is particularly notable as the metallic character and reactivity of these elements increase down the group, corresponding with a decrease in ionization energy.

In contrast, high electronegativity does not apply to alkaline earth metals as they are less electronegative than many other elements. Their large atomic size contributes to the lower ionization energy, but it is the low ionization energy itself that is the primary factor in their reactivity. Additionally, while alkaline earth metals can form covalent bonds, this is not their predominant mode of reactivity, as they typically engage in ionic bonding by losing electrons to achieve stability.