d orbital [ENDORSED]

[Cyianna 2F]

Why do elements in the d orbital begin with 3d instead of 4d, since the d orbital begins in the 4th period?

[Rucha Kulkarni 2A]

Because minimum energy level for d-orbital is 3, when n=3 the values for l begin from zero i.e. l=0,1,2. (Where l=2 is the d-orbital)
So you'd have to fill up the 3d orbital at lower energy level before you move to the 4d orbital.

[Payton Schwesinger 1J]

The 4s orbital is at a lower energy than the 3d, so the 4s fills up before the 3d. Once the 3d fills up then it switches back and 3d is at a lower energy level than 4s. It is the same as this for the rest of the periods, so usually the d orbital is one number behind whichever period you are dealing with. (if dealing with period 5, the d orbital is 4d)