Question

how would you justify the presence of 18 elements in the 5th period of periodic table

Answer 1

While filling 5th shell according to aufbau principle 5s,5p.4d filled so 2 +6 +10 =18 electrons or elements are present in 5th shell.

Answer 2

Explanation:

For 5 the period, principal quantum number, n=5 and values of azimuthal quantum no., l =0,1,2,3

According to Aufbau principle, filling of orbitals in sub-shells takes place in increasing order of energy of sub-shell. Since energy of 4f sub-shell is higher than 5s sub-shell, the sub-shells available for filling are 5s,4d 5p.

∴ total no. of orbitals=1 for 5s+5 for 4d+3 for 5p=1+5+3=9

∴ total no. of electrons that can be accomodated in 9 orbitals =2×9=18

Hence, the no. of electrons or elements in 5

th

period are 18.