Question

Why is electronic configuration of copper different?

Answer 1

There are two main exceptions to electron configuration: chromium and copper. In these cases, a completely full or half full d sub-level is more stable than a partially filled d sub-level, so an electron from the 4s orbital is excited and rises to a 3d orbital.

Answer 2

because they have incomplete orbitals but they come in excited state and obtain one electron from its weaker orbitals to complete half orbital which is stable.