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

The rules for the writing of the distribution of electrons in various shells for the first eighteen elements are given below:

(i) The maximum number of electrons present in a shell is given by the formula-2 n²

∵ n = orbit number i.e., 1, 2, 3

∵ Maximum number of electrons in different shells are:

K shell n = 1 2n² => 2(1)² = 2

L shell n = 2 2n² => 2(2)² = 8

M shell n = 3 2n² => 2(3)² = 18

N shell n = 4 2n² => 2(4)² = 32

(ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.

(iii) Electrons are not accommodated in a given shell unless the inner shells are filled. (The shells are filled step-wise).