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

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

(i) The maximum number of electrons present in a shell is given by the formula \( 2n^2 \) , where ‘n’ is the orbit number or 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 orbit 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 step-wise manner.