why in the building of the atom, the filling of 4s-orbital take place

1.	why in the building of the atom, the filling of 4s-orbital take place before 3d-orbital?
Answer» Yes, becoz according to afbau principle, electron first occupy the lowest energy orbital and then filled to higher energy orbital, only after the lower one filled......... For ex- 4s=4+0=4....... For ex- 3d= 3+2=5..... As 4s orbital is lower energy orbital hence, it will filled first............... HOPE IT HELPS? Ssooo the movement is 1s then 2s then 2p 3s then 3p 4s then 3d 4p 5s .... Make a table1s2s 2p3s 3p 3d4s 4p 4d 4f5s 5p 5d 5f6s 6p 6d 7s 7p

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