When an atom of magnesium forms an ionic bond in which has the same electron configuration as noble gas neon, it loses two electrons. This is because magnesium has two electrons in its outermost shell, and when it loses these electrons, it is left with a full outer shell of eight electrons, which is the same electron configuration as neon. The loss of these two electrons results in the formation of a positive ion, or cation, of magnesium (Mg2+).