Question

Minimum atomic number which can change the present model of periodic table?
1) 119
2) 121
3) 132
4) 144

Answer 1

you can see that last elements in 7th group is Og which atomic no is 118 .
if next element , I mean element which atomic number = 119
then , a new period will require for this elements

another way ,
maximum no of elements in 1st peroid = 2
maximum no of elements in 2nd period =8
max no of elements in 3rd period = 8
max no of elements in 4th peroid = 18
max no of elements in 5th period = 18
max no of elements in 6th peroid = 32
max no of elements in 7th peroid = 32
==================================
total no of elements = 118
hence, next 8th peroid for new elements which atomic no = 119

Answer 2

Answer:

121 element is the correct answer.

Explanation:

Present form periodic table has 7 periods. So, in order to change the present form of periodic table there should be 8 periods.

Now for 8th period,

we know,

energy levels are as follows: 8s 5g 6f 7d 8p *

now, as we start filling the electrons, 119th & 120th element/electron will come under 's-subshell' or 's' group/block which is not a new form it already exist in the modern periodic table. Now, as we further fill 121th element/electron in the 5g subshell, we get a new block i.e g-block.

Therefore, minimum atomic number which can change the present model of periodic table is 121.

*note:

How we decide the energy level of a period "nth"?

for that:

write: ns '''''''''''(n-2)g  (n-1)f  (n-1)d  np.