Answer: The electrical configuration of the elements provides the basis for the contemporary periodic table. The electrical configuration of the valence shell of the elements is repeated in such a way that elements with the same valence shell electrons fall under the same group when they are arranged in order of increasing atomic number. They have identical qualities because the number of valence shell electrons is the same.
Periodic qualities are those that have a regular gradation when moving from left to right in a period or from top to bottom in a group and are directly or indirectly related to their electronic configuration.