Give the atomic number of an element that has two electrons in orbital a but no electrons in orbital c. Which combination of quantum numbers is possible for an atom with five orbitals in one subshell? One of the most striking is the remarkable level of agreement between these configurations and the configurations we would predict. Orbitals that have the same value of the principal quantum number form a shell. The principal quantum number therefore indirectly describes the energy of an orbital. In atomic physics , higher n sometimes occur for description of excited states. For the 2s orbital, identify the quantum numbers of n and l.