Write about the electronic configuration of `1^(st)` and `2^(nd)` period.

Explanation

Electronic configuration of `1^(st)` period:
In `1^(st)` period only two elements are present. This period starts with the filling of electrons in first energy level, n=1. This level has only one orbital as I.s. Therefore it can accommodate two electrons maximum.
Electronic configuration of `2^(nd)` period:
In the `2^(nd)` period 8 elements are present. This period starts with filling of electrons in the second energy level, n=2. In this level four orbitals (one 2s and three 2p) are present. Hence the second energy level can accommodate 8 electrons. Thus, second period has eight elements.