3D - 2

while filling orbitals of Cu why do we put 1 electron in 4s and fill 10 electrons in 3d ?

while we know that according to n+l rule we must fill 4s completely; mean it should have been 4s with 2 electrons but in Cu 4s has 1 electron !!! WHY IS IT SO ??

Public Comments

1. 10 electrons in 3d is a more stable configuration because the orbital is filled. The gain in stability from completely filling the d orbital makes up for the energy penalty of promoting a 4s electron to a 3d orbital.
2. hi............ it is because half filled orbital is more stable.