Explain the electronic configuration of elements according to groups in the extended periodic table.

(N/A) Similarity in elements of the same group: Elements in the same group or vertical column have the same valence shell electronic configuration. Elements in the same group have the same number of electrons in their outer orbitals and exhibit similar chemical properties. For example,the valence shell electronic configuration of group-$1$ elements (alkali metals) is $ns^1$.
The names,symbols,and electronic configurations of group-$1$ elements are given in the table below:

Atomic Number and Symbol	Electronic Configuration
$3, Li$	$1s^2 2s^1$ or $[He] 2s^1$
$11, Na$	$1s^2 2s^2 2p^6 3s^1$ or $[Ne] 3s^1$
$19, K$	$1s^2 2s^2 2p^6 3s^2 3p^6 4s^1$ or $[Ar] 4s^1$
$37, Rb$	$1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 5s^1$ or $[Kr] 5s^1$
$55, Cs$	$1s^2 2s^2 2p^6 3s^2 3p^6 3d^{10} 4s^2 4p^6 4d^{10} 5s^2 5p^6 6s^1$ or $[Xe] 6s^1$
$87, Fr$	$[Rn] 7s^1$