Summaries the rule for writing of …

the following rules are followed for writing the number of electrons in different energy levels or shells.

(i) the maximum number of electrons presents in a shell is given by the formula 2n² where ′n′ is the orbit number of energy level index 1,2,3... hence the maximum number of electrons in different shells are as follows : 
First orbit or K-shell will be = 2 × 1² × 2 Second orbit or L shell will be = 2 × 2² = 8 third orbit or M shell will be = 2 × 3² = 18 fourth orbits or N-Shell will be = 2 × 4² = 32 and so on.

(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. That is the shells are filled in a stepwise manner.