Explain how does the filling of electrons takes place in the modern periodic table across: i. Second period ii. Third period

Question

Explain how does the filling of electrons takes place in the modern periodic table across:

i. Second period

ii. Third period

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Salim Ahmed Kawsar · Answer 1 · Feb 05, 2023 15:29:48

i. Filling of electrons in the second period:

In the second period, electrons are filled in the second shell i.e., n = 2.
This shell can accommodate a maximum of eight electrons and gets filled as the atomic number increases along the second period.
The second period begins with Li (Z = 3): 1s² 2s¹ and ends up with Ne (Z = 10): 1s² 2s² 2p⁶.
Neon has complete octet with 8 electrons in its valence shell. Therefore, the second period contains eight elements.

ii. Filling of electrons in the third period:

The third period corresponds to the filling of the third shell i.e. n = 3.
The third period also contains eight elements.
It begins with the filling of electrons in the first element Na (Z = 11) : [Ne] 3s¹ and ends with the last element Ar (Z = 18) = [Ne] 3s² 3p⁶.
The condensed electronic configurations for the elements of third period is [Ne] 3s^1-2 3p^1-6.

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