In d block chemistry, Copper and Chromium electron configuration do not follow the electron filling trend , why is this?

Copper has a [Ar]4s1 4d10 whereas Chromium has a [Ar]4s14d5 electron configuration as this d shell configuration of either half full d shell (5 electrons) with only one electron per orbital or fully full d shell orbital (10 electrons) makes it more energetically stable for the electron in 4s2 (trend in electron filling in d block metals) to go and make that half full or fully full shell and therefore yield 4s1 breaking the trend