A difficulty arises when we come to potassium. Potassium has an atomic number of 19. For potassium and calcium, the 4s orbital dips in energy below the 3d orbitals, and so electrons go into the 4s ...

This energy level model shows two electrons on the first energy level and six electrons on the second energy level. Since this atom has a total of eight electrons ... 4th Period: Potassium and Calcium ...