WHy is Copper an exception in electron configuration?
Copper is not an exception except in our minds. The exception lies in our attempt to explain electron configurations. In the case of Cu and Cr for the 3d series, they don't fall into our neat pattern; therefore, we call them exceptions. As to WHY, the best answer I can give is that the
1s2 2s2 2p6 3s2 3p6 3d10 4s1 of copper has a lower energy than any other combination including the one we might expect it to have; i.e.,
1s2 2s2 2p6 3s2 3p6 3d9 4s2. I often see texts say that the 3d orbital has a higher stability when it is half filled (in the case of the other exception of Cr) or completely filled (in the case of Cu). So in the case of Cr, the 3d and 4s are half filled; in the case of Cu the 3d is completely filled and the 4s is half filled. I hope this helps.
Copper is considered an exception in electron configuration because it does not follow the expected pattern based on the periodic table. In the case of copper, its electron configuration is 1s2 2s2 2p6 3s2 3p6 3d10 4s1.
Normally, one would expect copper to fill up its 3d orbital with 9 electrons and have an electron configuration of 1s2 2s2 2p6 3s2 3p6 3d9 4s2. However, that is not the case for copper.
The reason for this exception lies in the energy levels of the orbitals. In the case of copper, the configuration 1s2 2s2 2p6 3s2 3p6 3d10 4s1 has a lower energy than the one we might expect it to have. The 3d orbital is actually more stable when it is completely filled or half filled.
So, in the case of copper, the 3d orbital is completely filled with 10 electrons, and the 4s orbital is half filled with 1 electron. This configuration is more energetically favorable, leading to the exception.
It's important to note that these exceptions are specific to how we interpret electron configurations and explain them. In reality, the behavior of copper's electrons follows the laws of quantum mechanics, and the concept of exceptions arises from our attempts to simplify and explain electron configurations based on patterns in the periodic table.