expected electron configuration of chromium [ENDORSED]

[Rain Taganas 1J]

Why is the expected electron configuration for chromium different from the observed electron configuration? The expected configuration is [Ar]4s2,3d4 and the observed configuration is [Ar]4s1,3d5.

[skalvakota2H]

Chromium acts like an exception in the sense that 3d5 is a more stable configuration than 3d4, the reason being that an exactly half filled sub-shell is partially full is more stable than a partially sub-shell. As a result, an electron from the 4s orbital is excited and rises to the 3d orbital.

[Katherine Jordak 1H]

For similar reasons, Copper is also an exception to that normal electron configuration rule. Its electron configuration is [Ar]4s1,3d10. A completely filled sub-shell will be more stable than a partially filled one.

[deeksha1I]

Are copper and chromium the only elements that are like this?