An element want to gain a full octet (8 valence(outer shell only) electrons) as fast as possible. group metals 1,2, or 3 lose 1,2, or 3 electrons because they are 1, 2, or 3 electrons away from a full octet. gaining electrons for either of these requires 7, 6, or 5 more electrons. For example Al loses 3 electrons to have a full octet (Al+3) while Cl gains 1 electron for a full octet(Cl-1). The point is Cl now has the same number of electrons as the noble gas next to it and Al has the same number of electrons as the noble gas before it. As for carbon group elements, they take or lose 4 electrons depending on the question that's being asked. don't mind the transitional metals, there's no method to predict their charge since some have a multitude( Cu+2 Or +3). Your teacher should be giving you a chart for these.
