Explain Why Magnesium Chloride Has No Overall Charge?

Because they cancel out. There are two chlorine ions for each magnesium ion.

The charge on each magnesium ion is:   2+
the charge on each chloride ion I:   1-

so therefore:  +2 -1 -1 = 0
Magnesium (+2) + Chloride (-1) + Chloride (-1)

Ok, I'm very bad at explaining, but hope this helps.. XD