How does the electronic configuration of an atom relate to its position in the Modern Periodic Table?

Explanation

Th electronic configuration of an elment tells us two thing: the number of electron shells and the number of valence electrons in one atom of the element.
(i) The number of electron shells in an atom of the element gives us the period number of the elemnet in the periodic table. If an element has 2 electron shells in its atom, it belongs to 2nd period, if an element has 3 electron shells, it belongs to 3rd period, and so on. For example the electronic configuration of carbon element is `underset(2)(K) underset(4)(L)`. Since the carbon atom has two electron shells (`K` and `L`) , therefore it belongs to 2nd period of the periodic table.
(ii) The group number of an element in the periodic table having up to two valence electrons is eual to the number of valence electrons. If an element has 1 valence electron, it belogs to group 1 and if the element has 2 valence electrons then it will be in group 2 of the periodic table. For example, the elecronic configuration of sodium element is `underset(2,8,1)(K L M)`. Since sodium has 1 valence electron (in `M` shell) so it belongs to group 1 of the periodic table.
(iii) The group number of an element having more than 2 valence electrons is equal to the number of valence electrons plus 10. If an elemnet has 3 valence electrons it group number will be `3+10=13`, if the element has 4 valence electrons then its group number will be `4+10=14`, and so on. For example, the electronic configuration of aluminium is `underset(2,8,3)(K L M)`. SInce aluminium has 3 valence electrons ( in `M` shell) therefore, it belongs to group number `3+10=13` of the periodic table.