3dz2 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 gold area is where an electron has a positive wavefunction, and the red area is where the wavefunction is negative. The 3dz2 (or 3dzz) orbital is part of the 3d shell, which contains five orbitals in total. The 3d shell is partially full in the first row of transition metals. These metals typically form coloured compounds as electron transitions between 3d orbitals absorb some visible wavelengths of light.