A vertical column of the periodic table, sometimes called a family because the elements in each group often have similar characteristics. Each of the elements in groups 1A through 8A contain the same number of electrons in its outer shell. For example, all of the elements in group 4A have four electrons in their outer shell. Most of the elements in the B groups contain one or two electrons in their outer shell. However, unlike Group A elements, Group B elements often use one or more of the electrons in their second to last shell to bond with other atoms and form new substances. See also Period, Valence Shell, and Chemical Bond.