Sodium and chlorine 		In the case of ionic bonding since metals typically have relatively good shielding and lower ionization energies, outer electrons are more easily removed (i.e., oxidation). Non-metals have relatively poor shielding and higher electron affinities. That means they are capable of accepting additional electrons (i.e., reduction).

Another way to look at that is to examine typical electron configurations for such elements, say, sodium and chlorine:

[Ne]3s1 and [Ne]3s23p5

Both of these configurations are one electron different from a full s-p complement of 8 electrons. If the sodium loses one electron and the chlorine gains one the resulting ions will each have eight electrons in the highest occupied energy level (an "octet"). We can represent this in another way using a diagrammatic form of the electron configuration called an "orbital diagram".