Why is copper called a special case of Hunter Rule? What is the connection between his electronic configuration and Hunter's rule?
The element in front of copper is nickel, and its electronic configuration is 3d84s2, so theoretically the electronic configuration of copper should be 3d94s2. However, because 3d9 is only one electron away from 3d 10 of the whole structure, it is finally rearranged into 3d 104s 1. This rearrangement phenomenon is the embodiment of Hunter's law: when the electron appears half-full, full or empty in the equivalent orbit.