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Q. 6.     Summarise the rules for writing of distribution of electrons in various shells for the first eighteen elements.

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The Bohr and Bury scheme for the distribution of electrons in an atom is based on the following rules :
1. The maximum number of electrons which a shell can have is represented by 2n^2, where n is the quantum number of that particular energy shell. Thus, the maximum number of electrons in the first four shells are :
1st (K) shell 2 x 1^2 = 2
2nd (L) shell 2 x 2^2 = 8
3rd (M) shell 2 x 3^2 = 18
4th (N) shell 2 x 4^2 = 32

2. The outermost shell, which is also called valence shell, can have a maximum of 8 electrons.

3. If permitted by rule 1, The shell inner to the outermost shell (the second last shell ) can accommodate a maximum of 18 electrons.

4. Electrons are not taken in unless the inner shells are filled, i.e., the shells are filled in a step-wise manner.   

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Pankaj Sanodiya

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