Why is the electron configuration of chromium?
It is energetically favored.
Looking at the periodic table, you would expect Chromium to have this configuration:
Or, condensed using noble gases:
However, the actual configuration of Chromium is:
So why is this? It has to do with main the arrangement of sublevels in the electron cloud. Even though
This happens in Chromium, as one
#3d#orbital is slightly lower in energy, and minimizing repulsions in the #4s#orbital by moving one of the #4s#electrons to a close-lying #3d#orbital minimizes the ground-state energy of chromium.
- Hund's Rule: It is energetically favorable to maximize the spin state in a sublevel. Since two opposite spins result in a total spin of
#0#, maximizing this tends to require as many electrons in of same spin in different orbitals as possible. So, in this case, an electron moves to #3d#and is unpaired, therefore maximizing the spin state.
You will see a similar situation where an
In all of these scenarios, the new redistribution of the electron is energetically favorable compared to the predicted configuration.