Question

According to Aufbau's Rule, It must be 5d8 6s2.. Even if considering stability; In terms of exchange energy and pairing, 5d9 has only 1 free electron, and thus no exchanges are possible as all other 4 orbitals are fully filled;( Thus decreasing stability and increasing pairing energy ). Still, 5d8 6s2 seems more stable as more exchanges are viable in the d subshell and even 6s is fully filled.

The more general answer I have stumbled upon is that the orbitals have nearly the same energies so 1 electron jumps from 6s to 5d, but it seems to violate the fact that subshells seek to be half or completely filled, so either electron must not jump or both electrons must jump like in the case of Palladium. I am Ignoring the fact that 6s is left half-filled which decreases stability ( As the element seeks the most stable configuration, Using General concepts 5d8 6s2 seems more stable)

All over the internet, There are either 2 answers:

1)Unknown Stabilty
2)Solve Schrodinger Dirac's Equation

Can someone please explain this exception? (Maybe even correcting some of my errors above) Thanks in Advance!!

Answer 1

The electron configuration of Cr and Cu follows an exception to the Aufbau Principle due to the stability gained from half-filled or completely filled subshells. Electron-electron repulsions in the lower energy subshell cause the electron to shift to a higher energy subshell. This phenomenon explains the observed electron configurations of Cr and Cu.

Step-by-step explanation:

According to the Aufbau Principle, electrons fill orbitals in order of increasing energy. However, there are exceptions to this rule, such as the electron configuration of Chromium (Cr) and Copper (Cu). In the case of Cr, an electron shifts from the 4s orbital to the 3d orbital to achieve a half-filled 3d subshell, which is more stable.

Similarly, in the case of Cu, the electron configuration fills the 3d subshell completely for increased stability. These exceptions occur because the electron-electron repulsions in the 4s orbital of Cr and 5s orbital of Cu are larger than the energy difference between the subshells.