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why in the 3rd period there is 8 elements and not 18th elements ? .. Give reason ..

Actually 3rd shell should contains 18 elements but there are 10 electrons which are found to have high energy equivalent to energy of 4th shell. So these electrons are not counted in the 3rd shell. Hence, only 8 electrons are in 3 rd shell resulting 2, 8, 8, 18, electronic configuration. 

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 previously i recieved dis answer for de Q .. (The modern periodic table is arranged in order of increasing atomic number and the elements of the similar properties are placed in the same group. In this way modern periodic table is arranged and from this arrangement we get 2 elements in first period, 8 elements in second and third period , 18 elements in 4th, 5th period and so on. )

i dnt feel dat dis a appropriate for my query , plz help me out with this Q ...

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No. of elements in a period is determined by the maximum no. of electrons that each shell can contain

there4, K shell-2electrons -> so 2 elements in 1st period

and so on

  • -6

because there r mettaloids also place ..and it is not calculated

hence there r only 8 elements

hope this helps...thumbs up pls!!!

  • -4

*metalloids

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