first:Aluminum electronic configuration- 1s2 2s2 2p6 3s2 2d1second:Aluminium electron configuration:1s2 2s2 2p6 3s2 3p1
Electron shells are normally extraordinary in the best way they fill upIn chromium, the sixth electron within the 3d shell feels sufficient repulsion from the opposite 5 that it is happier hanging out in 4s insteadBut it surely's a detailed call, and the configuration may range in some compounds from the structure of the raw aspectWhich is more often than not why chromium chemistry is so exciting, with several oxidatio states.
