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IT IS SAID THAT AN ATOM CONTAINS 8 ELECTRONS IN THE OUTER MOST SHELL(EXEPT H &He)EVEN IF THE NUMBER OF ELECTRONS IN A SHELL IS GIVEN BY THE FORMULA 2(n*n). can u please explain why is it so?
The number of elements in these periods is based on the way electrons are filled into various shells. The maximum number of electrons that can be accommodated in a shell depends on the formula 2n2 where 'n' is the number of the given shell from the nucleus.

For example,

K Shell - 2 x (1)2 = 2, 1st period = 2 elements.

L Shell - 2 x (2)2 = 8, 2nd period = 8 elements.

M Shell - 2 x (3)2 = 18, but the outermost shell can have only 8 electrons, so the third period also has only 8 elements.


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