How does the electronic configuration of an atom of an element related to its position in the modern periodic table ? Explain with one example.

Explanation

The position of elements depends upon number of valence electrons which depend upon electronic configuration. Those elements which have same valence electrons, occupy same group.
Those elements which have one valence electron belong to group 1.
Elements which have two valence electrons belong to group 2.
Period number is equal to the number of shells.
Example : Atomic number of sodium (Na) is 11, so electronic configuration will be 2, 8, 1. Sodium has one valence electron in valence shell so it belongs to group 1. As sodium has three shells, so it belongs to `3^(rd)` period.