[Winga]

Before filling electrons in 3d & 4s orbitals, 4s' orbital energy level is lower than that of 3d's. Why?

After filling e- in these obitals, 4s e-s experience greater repulsive force from the inner e-s than that of 3d e-s. Why?

Why filled 4s orbital becomes higher energy state (less stable), but we always say full-filled orbital having extra stability?

[Winga]

4s, but why?
What is penetrating power?

[ssssss]

Before filling electrons in 3d & 4s orbitals, 4s' orbital energy level is lower than that of 3d's. Why?

After filling e- in these obitals, 4s e-s experience greater repulsive force from the inner e-s than that of 3d e-s. Why?

Why filled 4s orbital becomes higher energy state (less stable), but we always say full-filled orbital having extra stability?

For the energy of 4S being lower than that of 3d.Check out their radial function curves.These curves show that the S electrons have considerable presence near the nuclei as compared to the d orbital.Even if you see their total probability Distribution curves you will Find the same results.Reason,the d orbital starts from more distance from nuclei as compared to S orbital.But you need not go in Detail.


Why filled 4s orbital becomes higher energy state (less stable), but we always say full-filled orbital having extra stability?


With which orbitals are you Making this Comparison?


After filling e- in these obitals, 4s e-s experience greater repulsive force from the inner e-s than that of 3d e-s. Why?


I think this is to Do with the Penetration of Electrons in an atom.The inner electrons are more penetrated to the nucleus as compared to the outer ones causing less influence of the nucleus on the outer or less penetrated electrons,causing more interaction between these electrons among themselves.Hence resulting in the Domination of the repulsive force.

Get thorough with Phenomenon of Shielding effect.