Here's why:

* Electron Configuration: Alkaline earth metals have two electrons in their outermost energy level (valence electrons).

* Tendency to Lose Electrons: They tend to lose these two valence electrons to achieve a stable, full outer shell like the noble gases.

* Formation of Cations: When they lose these electrons, they become positively charged ions (cations) with a +2 charge.

Examples:

* Magnesium (Mg) forms Mg²⁺

* Calcium (Ca) forms Ca²⁺

* Barium (Ba) forms Ba²⁺