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

Answer : The following rules are followed for writing the distribution of electrons in different energy

levels or shells for the first eighteen elements :

(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,

(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.

Distribution of electrons in various shells for the first eighteen elements
Element	Symbol	Atomic Number	Number of Electron	Distribution of electrons K L M N
Hydrogen Helium Lithium Beryllium Boron Carbon Nitrogen Oxygen Fluorine Neon Sodium Magnesium Aluminium Silicon Phosphorus Sulphur Chlorine Argon	H He Li Be B C N O F Ne Na Mg Al Si P S Cl A	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18	1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18	1 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 2 - - 1 2 3 4 5 6 7 8 8 8 8 8 8 8 8 8 - - - - - - - - - - 1 2 3 4 5 6 7 8 - - - - - - - - - - - - - - - - - -

This is an answered question from Chapter 4. Structure Of The Atom of CBSE Class 9th Science

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