Question

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

Answer 1

The following rules are followed for writing the number of electrons in different energy levels or shells.

i) The maximum number of electrons present in a shell is given by the formula 2n², where ‘n’ is the orbit number or energy level index, 1,2, 3… Hence the maximum number of electrons in different shells are as follows:

First orbit or K-shell will be = 2 × 1² × 2, Second orbit or L shell will be = 2 × 2² = 8, third orbit or M-shell will be = 2 × 3² = 18, fourth orbit or N-shell will be = 2 × 4² = 32 and so on.

ii) The maximum number of electrons that can be accommodated in the outermost orbit is 8.

iii) Electrons are not accommodated in a given shell, unless the inner shells are filled. That is the shells are filled in a step-wise manner.