Calcium (Ca) typically forms a +2 charge ion. This occurs because calcium is an alkaline earth metal located in group 2 of the periodic table. Atoms of calcium have two electrons in their outermost shell (the third energy level) which are 4s electrons.
During chemical reactions, calcium tends to lose these two outermost electrons to achieve a stable electron configuration similar to that of the nearest noble gas, argon. When calcium loses these two electrons, it becomes a calcium ion with a +2 charge (Ca2+). This process is driven by the atom’s desire for stability, as ions with a full outer shell are generally more stable. Therefore, the calcium ion, which has lost two electrons, achieves a stable electronic configuration.