Why isn't chromium's electron configuration 2, 8, 12, 2?

[JoshuaFarrell]

Its actual electron configuration is 2, 8, 13, 1 even though Vanadium's electron configuration is 2, 8, 11, 2 and Manganese's is 2, 8, 13, 2.

 

[dextercioby]

It has to do with the 3 Hund's rules and the fact that 5 electrons in all 5 d orbitals form a lower energy configuration. The same happens with 10 electrons and the configuration of Copper.