How would you write the following elements as an ion: S, Mg, Br, Al?
Well, metals tend to lose their valence electrons.........to give the electronic configuration of the preceding Noble gas.
And non-metals tend to gain valence electrons, so as to achieve the electronic configuration of the next Noble gas.
And finally aluminum, loses three electrons to form
In all these instances, the metal, electron-rich, tends to be reducing. And the non-metal, electron poor on account of its high nuclear charge, tends to be oxidizing. Capisce? How did I use the Periodic Table in this answer?