The vertical columns of the periodic table are called groups or families.

Changes in the labelling of these groups has caused confusion.

The traditional American pattern [CAS(Chemical Abstract Service) system] for the identification of groups is shown as the red number over the columns in the diagram below. The new IUPAC system (Arabic numerials) is shown in black. Some tables will be shown using group numbers using the old IUPAC system, those are shown in blue on the table.