4d electron orbitals, 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. Four of the five 4d orbitals are made up of four bi-lobed lobes, centred on the nucleus. The orbital at top comprises two bi-lobed lobes with a concentric pair of equatorial rings. The 4 shell also contains one spherical 4s orbital and three lobed 4p orbitals, both at a lower energy, and seven lobed 4f orbitals at a higher energy level (not seen). The 4d shells are partially full in the second row of transition metals, which typically form coloured compounds as electron transitions between 4d orbitals absorb some visible wavelengths of light.