Question

How will you justify presence of 18 elements in 5th period and presence of 32 elements in 6th period.

Answer 1

Dear student,

Justifying the presence of 18 elements in 5th period:
Principal quantum number (n ) is for 5^th period=5
values of azimuthal quantum number( l) = 0, 1, 2, 3
According to Afbau rule filling of orbitals in sub-shells takes place in order of
increasing energy of the sub-shell.
The sub-shells available for filling are 5s, 4d and 5p and energy of 4f sub-shell is
higher than 5s sub-shell.
Number of orbitals
For 5s=1
For 4d=5
For 5p=3
Total number of orbitals =1+5+3=9
Each orbital can contain maximum two electrons hence; total number of electrons in 9 orbitals is 18.
So, the number of elements in 5^th period is 18.


Justifying the presence of 32 elements in 6th period:
Principal quantum number (n) is for 6^th period=6
6th period contains s, p, d and f block elements so that electrons can fill in all these sub-shell.
Number of electrons for s, p, d and f are
s=2 .p=6, d=10 and f= 14
Total number of electrons in these orbitals are=2+6+10 + 14=32
So, the number of elements in 6^th period is 32.
Regards,