How do you know the charge of polyatomic ions?

Charge of monatomic ions?

• What charge do monatomic ions of Family IA exhibit? Why? What charge do monatomic ions of family ions of Family VIIA exhibit? Why? I know from my notes the first one the charge is 1. But I don't know why? Does it have to do with electronegativity? As for the second one I think I may have made a mistake when I was copying the board because I have Family VIIIA charge is -1. And I think that -1 charge may be for Family VIIA instead. Help please! =)

• Answer:

  I don't like giving answers for student assignments but I'll give you a hint: It has to do with valence electrons. Atoms like to have 8 valence electrons, so they will gain or lose electrons to try and fill their valence. So for example group 2 elements (Family IIA) have a charge of +2 in ion form because normally they have 2 valence electrons, but if they give those 2 electrons away then they will have 8 (it seems like they would have none, but they have 8 in the next s and p orbitals). So group 2 elements try to lose 2 electrons... so since they are losing 2 negative charges they will be left with a 2+ charge Family IA has charge 1+ Family VIIA have 1- (this means they gain an electron.... so try to figure out why that would happen)