Similarly, second and third periods can accommodate 8 and 18 electrons respectively. Since their outermost shells can contain only 8 electrons, there are only 8 elements in both the periods. -pllz explain this again.
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Using the formula...
2n2.
For second period...
n=2
Hence the maximum possible number of electrons in 2nd period = 2 x (2)2 =2 x4 = 8.
For 3rd period..
n=3
Hence the maximum possible number of electrons in 3rd period = 2 x (3)2 = 18