Question

How many energy levels are partially or fully occupied in a neutral atom of calcium?

Answer 1

18 I think. Essentially because there are so many more orbitals used by the molecules placed in the series. You will see that group 1-8 molecules always have a number of valence electrons equal to the group number. This reflects s and p orbital useage. Once d and f orbitals begin to be needed, the atoms become much more complex.