The rules for writing of the distribution of etectrons in various shells for the first eighteen elements are given below.
`to` Ifn gives the number of orbit or energy level, then `2n^(2)` gives the maximum number of electrons possible in a given orbit or energy level. Thus,First orbit or K-shell will have 2 electrons,
Second orbit or L-shell will have 8 electrons,
Third orbit or M-shell will have 18 electrons.
`to` If it is the outermost orbit, then it should have not more than 8 electrons.
`to ` There should be step-wise filling of electrons in different orbits, ie. electrons are not accompanied in a given orbit if the earlier orbits or shells are incompletely filled