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.

Why is copper anomalous electron configuration?

Copper show abnormal electronic configuration because it is more energy efficient to have a full lower energy orbital than high energy orbital. 4s has higher energy than 3d when it contains electrons i.e. copper with [Ar] 3d^10 4s^1 configuration is in lower energy state than copper with [Ar] 3d^9 4s^1 configuration.

Why do Cu and Cr have exceptional configuration?

The order of filling of electrons occupying the 3d subshell gets concerned in chromium and copper and because of distress in 3d subshell, these elements possess exceptional configuration.

BRIAN M. Copper is in the ninth column of the transition metals in the d block of the fourth energy level of the periodic table. This would make the electron configuration for copper, 1s22s22p63s23p64s23d9 or in noble gas configuration [Ar] 4s23d9 .