What is the electron configuration for Fe+?
Electronic Configuration of Fe+ is-
##1s^2 2s^2 2p^6 3s^2 3p^6 4s^1 3d^6##
4s orbital is filled before the 3d orbital because of its low energy level than 3d. And electrons first are removed from 4s orbital.
Reason for low energy level of 4s-
As we obey the Aufbau Principle, it says that electrons are first filled in low energy levels and then to high energy levels.
Bohr-Bury rule or the (n+l) rule is used for this.
Bohr-Bury rule determines the energy level of any orbital.
In 4s, n=4 and l=0. So, n+l = 4+0 = 4.
In 3d, n=3 and l=2. So, n+l = 3+2 = 5.
Therefore, 4s is on low energy level than 3d.