Now, before we can talk about electron configurations, realize first that Mendeleev organized the elements in the periodic table through periodic law. In periodic law says that when arranged by increasing atomic weight, elements in the same group share similar chemical properties.
These properties would influence their electron arrangements and by extension, their configurations. It would affect their trends and reactivity and their atomic structures.
So remember, in order to 1st understand electronic configurations, we need to go into periodic law 1st and it helps us to understand how the periodic table itself is organized.