All of the groups on the periodic table are indicated by a combination of a
number and a letter. For instance, the alkali metals group is designated 1A. The
alkaline earth metals group is 2A. All of the groups in the d area have a
designation that ends in a B. To the right of the d area, designations ending in A
resume. The group containing aluminum is 3A, and so on up to 7A (the
halogens) and 8A (the noble gases). Notice that for the A groups, the number
represents the number of valence electrons possessed by elements in that group.
So a lithium atom (1A) has 1 valence electron, a carbon atom (4A) has 4 valence
electrons, and an iodine atom (7A) has 7 valence electrons.
Some Important Element Groups