Question

Why should electron enter into 4s, instead of 3d after 3p​

Answer 1

Answer----->

By Afbau principle:-

We know that electrons are filled in orbitals with increasing order of their energies .

So, by( n+l) rule we can find the energies of orbitals .

So, for 4s -. n=4. s=0.

So, n+l=4

For 3d. n=3. s=2

n+l=5

So, by this we can conclude that 4s orbital have less energy,so, by afbau's principle electron should go in 4s orbital firstly.

Now you have another question in your mind that 3p and 4s have same values of n+l . Then in which orbital electron should go firstly .

So, in this case we have to take value of n.

3p have less value of n so, in 3p orbital electron should go firstly.