Redox-
Reaction
= Electron-Transfer-Reaction
In this reaction the electron donor substance (i.e. Mg) is oxidized while an electronen acceptor substance (i.e. O) is reduced. Example: Combustion of magnesium (left photo): Right: In the PSE the noble gas neon (¹⁰Ne) is placed in the middle between (¹²Mg) and (⁸O). A magnesium atom (¹²Mg) has 2 electrons more than a neon atom (¹⁰Ne).  Mg and O exchange 2 electrons.
¹²Mg donates two of its electrons while ⁸O accepts them.    Each electron has one negative unit of charge. That means: The O atom has become an oxide ion with a double negative charge (O^2-) and  the Mg atom has become a magnesium ion with a double positive charge (Mg²⁺).
              Both attract each other to form a unit cell of magnesium oxide.