How can you tell valence electrons from the periodic table?
For the representative elements, groups 1 and 2, and 13-18, the valence electrons can be determined from the group number.
For groups 1 and 2, the number of valence electrons for elements in those groups is 1 and 2 respectively. For groups 13-18, subtract 10 to get the number of valence electrons for elements in those groups, so group 13 elements have 3 valence electrons, and group 14 elements have 4 valence electrons, and so on.
If you use a periodic table with A and B groups, the A groups are the representative elements. The Roman numerals associated with the A groups give the number of valence electrons for the elements in those groups.