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

(1) The maximum possible number of electrons which can be found in any level of the atom of an element is given by 2n² (where n is the number of that energy level). By using this relation, we will find that :

(a) the maximum possible  number of electrons which can be accommodated in 1st energy level K shell, where n= 1,

2n² = 2 X (1)² = 2 X 1 = 2. Hence, K shell can have a maximum of 2 electrons.

(b) the maximum possible  number of electrons which can be found  in 2nd energy level, L shell, where n = 2 , 2n² =2 X (2)² = 2 X 4 = 8. L shell can have a max 8 electrons.

(c) the maximum possible  number of electrons which can be found  in 3rd energy level M shell, where n = 3, 2n² = 2 X (3)² = 2 X 9 = 18. M shell can have a max 18 electrons.

(d) the maximum possible  number of electrons which can be found in 4th energy level N shell, where n = 4. 2n² = 2 X (4)² = 2 X 16 = 32. N shell can have a max 32 electrons.

(2)The electrons in an atom can not occupy a newer shell unless all the inner shells filled with electrons. This means that first, all the electrons fill K shell, then L shell, then M shell, then N shell, and so on.

(3) The electron in the outer shell of the first 18 elements cannot be more than 8 electron in the outermost shell