Atomic Theory

X                                                          loses two electrons                                                         

The atom of the magnesium loses its outermost two electrons and therefore no longer remains neutral (it no longer has an equal number of protons and electrons). It then contains more protons (positively charged particles) than electrons and therefore becomes a dipositively charged ion – Mg2+.  It could also be called a divalent cation.

The electrons lost by the magnesium could in turn be gained by another atom which needs to gain electrons to get a stable outer electronic configuration. An oxygen atom having an atomic number of  8 and therefore an electronic configuration of (2 6) could, for example, gain these electrons.

      Oxygen atom                                                                Oxide  ion