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

Explanation

Bohr and Bury scheme for the distribution of electrons in an atom is based on the following rules :
(i) The maximum number of electrons which a shell can have is `2n^(2)` where n is the quantum number of that energy shell . So , the maximum number of electrons in various shells are ,
1st (K) shell `2 xx 1^(2) = 2`
2nd (L) shell `2 xx 2^(2) = 8`
3rd (M) shell `2 xx 3^(2) = 18`
4th (N) shell `2 xx 4^(2) = 32`
(ii) The outermost shell (also called valence shell) can have a maximum of 8 electrons . Next to the outermost shell (called penultimate shell) can accommodate a maximum of 18 electrons , if permitted by rule (i) .
(iii) Electrons are not accomodated in a given shell unless the inner shells are filled . That is the shells are filled in a step-wise manner .