Question

why is 4 s sheel filled befor 3 d shell ? Explain inform of n+ 1 Rule.​

Answer 1

Answer:

electrons are filled in orbital according to the (n+l) rule.

So, here it is, as you may aware of what is ‘n’, it is the shell number, means the principal quantam number. And ‘l’ is the subshell value i.e. azimuthal quantam number, which is 0 for s-subshell, 1 for p-subshell, 2 for d-subshell and 3 for f-subshell.

S, now, lets see why 4s is filled before 3d.

Lets apply (n+l) rule on both-

For 4s- n+l => 4+0 = 4

For 3d- n+l => 3+2= 5

It is clear now, that the energy of 3d is larger than the energy of 4s, thats why 4s is filled before 3d.