The vertical columns on the period table are called groups. There are 18 groups on the periodic table, and elements that are members of the same group share similar traits.
All elements in the same group have the same number of electrons in their outer electronic shell. Because of this, members of the same groups tend to receive and release the same number of electrons, which means elements in the same group share reactivity traits. For example, the noble gasses are a group, and none of these gasses react with any other elements because they all have full outer electronic shells.
