orbitals

[Savannah Mance 4G]

Can someone explain to me why s-electrons have a lower energy than p or d electrons. I knew that inner electrons shield the outer electrons from electrostatic attraction of the positive nucleus so I thought this meant they needed a higher energy to shield.

[Vincent Leong 2B]

I believe the energy of the orbitals sort of has to do with the primary quantum number that each orbital begins with. The smallest principle quantum number for the s-orbital is 1, p-orbital is 2, d-orbital is 3, and f orbital is 4. It also has to do with their 3D configurations but I'm not too sure how they actually vary in strength in a 3D model.