Final answer:
Elements in the same column on the periodic table, referred to as 'groups', have the same number of valence electrons. These groups contain elements with similar chemical properties and are numbered 1 through 18.
Step-by-step explanation:
On the periodic table, the elements in the columns have the same number of valence electrons. The vertical columns are called groups or families, and there are 18 of them, numbered from 1 to 18 from left to right. Each group contains elements with similar chemical properties, and this similarity is because they have the same number of electrons in their outer shell, or valence shell. For example, Group 1 contains the alkali metals like lithium (Li) and sodium (Na), which all have one valence electron leading to similar bonding behaviors. The chemical behavior within groups is so consistent that even predictions about the properties of undiscovered elements can be made based on their expected group placement.