Valence is related to the number of electrons in the outside shell (sometimes the outide two shells). For 1A, IIA, IIIA elemenets the valence is the same as the numbrer of electrons in the outside shell.; i.e., 1, 2, or 3+. For elements in the V, VI, or VII columns, it is the negtive pf the number of electrons needed to make 8 (-1 for Cl, -2 for O, -3 for N) OR the number that may be lost (+3 or +5 for N, +4 or +6 for S,) Of course 0 for group VIII. You may be using another method for numbering the columns of the periodic chart. If so, Group IA, IIA, and IIIA above are 1,2, and 13 while IVA, VA, VIA, VIIA are 14, 15, 16, 17. Group VIII is 18. You can find a lot of information about valence by oogling it.
