Final answer:
The vertical columns on the periodic table are called groups or families, and they include elements with similar chemical properties. There are 18 groups, each with unique traits, such as the alkali metals in Group 1. Periods, in contrast, are seven horizontal rows that organize elements by atomic number.
Step-by-step explanation:
The vertical columns on the periodic table are commonly referred to by two names: groups and families. All the elements within a group or family share similar chemical properties because they have the same number of valence electrons. The periodic table consists of 18 of these groups, numbered from 1 to 18 from the leftmost side to the rightmost side. For instance, Group 1 contains the alkali metals, and Group 2 contains the alkaline earth metals, both exhibiting distinct chemical behaviors characteristic to their family. Each periodic table group signifies elements that exhibit similar chemistry, which is particularly evident in groups with common names such as the halogens in Group 17 and the noble gases in Group 18. The periodic table also includes horizontal rows called periods, which are numbered from 1 to 7. There's a clear distinction between the arrangement of groups and periods, where groups categorize elements based on chemical properties, while periods organize them by increasing atomic number.