The valence electrons are determined by the column that the element falls in.
Column 1 has 1 valence electron
Column 2 has 2 valence electrons
Column 13 has 3 valence electrons
Column 15 has 5 valence electrons
column 16 has 6 valence electrons
column 17 has 7 valence electrons
Elements are trying to become stable by filling the outer energy level. Columns 1,2,3 do this by losing 1,2 or 3 electrons and becoming positive ions. +1, +2, +3, respectively
Columns 15, 16, 17 do this by taking those electrons and becoming negative ions. -3, -2, -3. respectively.
