Summarize the rules for writing the distribution of electrons in various shells for the first eighteen elements.

(N/A) The rules for writing the distribution of electrons in various shells for the first eighteen elements are as follows:
$\rightarrow$ If $n$ represents the number of the orbit or energy level,then $2n^2$ gives the maximum number of electrons that can be accommodated in a given orbit or energy level.
Thus:
- The first orbit or $K$-shell can have a maximum of $2(1)^2 = 2$ electrons.
- The second orbit or $L$-shell can have a maximum of $2(2)^2 = 8$ electrons.
- The third orbit or $M$-shell can have a maximum of $2(3)^2 = 18$ electrons.
$\rightarrow$ The outermost orbit of an atom can accommodate a maximum of $8$ electrons.
$\rightarrow$ Electrons are filled in a step-wise manner in different orbits,starting from the innermost shell. Electrons do not occupy a higher energy shell until the inner shells are completely filled.