Explanation:
The representative elements are in columns A1 - A7. In an 18 column table the map is as follows:
A1 = column 1, hydrogen + alkali metals have 1 valence
A2 = column 2, alkaline earth metals have 2 valence
A3 = column 13, Boron family have 3 valence
A4 = column 14, Carbon group have 4 valence
A5 = column 15, Nitrogen family have 5 valence
A6 = column 16, Oxygen column - chalcogens have 6 valence
A7 = column 17, Fluorine column - halogens have 7 valence
The group number of the representative elements = the number of valence electrons.
