The different energy levels are written as follows—

(i) The electron in the given energy level or orbit are written according to the

formula 2n²—

In the first orbit (in K orbit) 2n² = 2 × 1² = 2 electrons

In the second orbit ( in L orbit) 2n² = 2 × 2² = 8 electrons

In the third orbit (in M orbit) 2n² = 2 × 3² = 18 electron

(ii) If there is an outermost orbit then the electron in it will not be more than 8.

(iii) Electrons are filled stepwise in different energy levels.