Answer
Atoms always try to maintain a full octet of electrons within their valence shell. Removing the 2 electrons, which can be found in the outer shell of alkaline earth metals, allows their previous full octet to be exposed.
Work Step by Step
The octet rule states that each atom wants 8 electrons in its valence shell. Since alkaline earth metals are unlikely to accumulate 6 more electrons to fill their shell, the ionization energy is low and they lose the electrons.
