3s electron orbital, computer model. An electron orbital is a region around an atomic nucleus (not seen) in which one or a pair of electrons is most likely to exist. The orbital is seen halved at right to show the concentric spherical nodes within it. The gold regions are where the electron has a positive wave function, and the blue area is where it has a negative wave function. The 3 shell also contains three 3p orbitals and five 3d orbitals at higher energy levels.