Lewis Dot Ionic

Use families on the periodic table to identify how many valance electrons (represented by dots) each element has. 

Metals will LOSE electrons

and

Nonmetals will GAIN electrons

Metals lose all their valance electrons (they have other electrons in layers beneath), which nonmetals gain until they have 8 valance electrons. They ionically bond in whatever ratio is necessary for all the metals to lose electrons and all nonmetals to gain until they get to 8.