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

The rules for writing of the distribution of electrons in various shells for the first eighteen elements are given below:
(i) The maximum number of electrons that a shell can accommodate is given by the formula ‘2n²’, where ‘n’ is the orbit number or energy level index (n = 1, 2, 3…).
The maximum number of electrons present in an orbit of n = 1 given by 2n² = 2 × 1² = 2 Similarly, for second orbit, it is 2n² = 2 × 2² = 8 For third orbit, it is 2n² = 2 × 3² = 18 And so on ….. (ii) The outermost orbit can be accommodated by a maximum number of 8 electrons.
(iii) Shells are filled with electrons in a step wise manner i.e., the outer shell is not occupied with electrons unless the inner shells are completely filled with electrons.

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