M19 Electronic configuration of scandium

Aim: To show how the orbital energy levels are filled for scandium
  For clarity only the energy levels up to 4p are illustrated here. The orbital energy levels are filled with pairs of electrons starting with the orbital with the lowest energy level, then the orbital (or orbitals) with the next highest energy level and so on.

In the case of scandium, 21Sc has 21 electrons filling the orbitals as follows:



Note that the 4s level is lower than the 3d level