What are groups or families on the periodic table?

Groups or families on the periodic table refer to vertical columns of elements that share similar chemical properties and behaviors. Each group or family typically contains elements that have the same number of valence electrons, which plays a significant role in determining how these elements react with others. For instance, all elements in Group 1 have one valence electron and are highly reactive, whereas those in Group 18 have full outer shells and are largely inert.

This vertical alignment signifies that as you move down a group, the elements display trends in their physical and chemical properties. For example, as you descend a group, you often observe increasing atomic radius and decreasing electronegativity.

On the other hand, horizontally aligned elements form rows known as periods, which indicate the number of electron shells, while sharing the same period doesn't mean they will exhibit similar properties, as the trends in properties change from left to right across the table. So, the definition of groups or families as vertical columns that share properties is foundational for understanding the organization of elements in the periodic table.