Question

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

Answer 1

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 × 1 2 = 2 

Similarly, for second orbit, it is 2n² = 2 × 2 2 = 8 

For third orbit, it is 2n² = 2 × 3 2 = 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. 

Answer 2

The rules for writing of the distribution of electrons in various shells for the first eighteen elements are given below.

→ If n gives the number of orbit or energy level, then 2n² 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.

→ If it is the outermost orbit, then it should have not more than 8 electrons.

→ There should be step-wise filling of electrons in different orbits, i.e., electrons are not accompanied in a given orbit if the earlier orbits or shells are incompletely filled.