Question

explain why the number of elements in third period is 8

Answer 1

Aufbau’s rule and the order of filling orbitals with electron is: - 1s 2s 2p 3s 3p 4s 3d 4p 5s 4d 5p 6s 4f 5d 6p 7s 5f 6d 7p 6f 7d 7f . . . . .

The maximum number of electrons that s, p, d and f orbitals can hold is 2, 6, 10 and 14 respectively.

2nd period begins with filling of ‘2s’ orbital and continue till filling of 2 p orbital. There are no orbitals between 2s and 2p and we can fill maximum of 2 electrons in s orbital and 6 in p, thus the number of elements in 2nd period is 8.

Answer 2

The number of electrons present in the outermost shell of an atom is given by the formula 2n2, where n stands for the number of the given shell from the nucleus of an atom. All the elements present in the 3rdperiod have 3 shells. Therefore , n = 3 ,

2n2 = 2 x (3)2 = 2 x 3 x 3 = 2 x 9 = 18

Since the outermost or valence shell can accomodate only 8 electrons . Therefore , the 3rd period contains only 8 electrons .

I hope it helps u dear ☺️.....