4fz3 electron orbital, illustration. 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 4fz3 orbital has a unique shape resembling four lobes elongated along the z-axis, two with a doughnut shape (or torus) around the nucleus in the x-y plane. The orbital is seen transparent at middle to show the axes of symmetry and the conical nodes and planar node can be seen at right. Nodes are the regions in an atom with zero electron density and where the electron is least likely to exist. For the 4fz3 electron orbital, 4 indicates that it is the fourth energy level, f indicates that the orbital is specifically an f-orbital, and (z3) indicates that the lobes of the orbital are oriented along the z-axis. The 4fz3 orbital can accommodate up to 2 electrons. The 4f orbitals are part of the 4 shell, which also contains one spherical 4s orbital, three bi-lobed 4p orbitals, and five daisy-shaped 4d orbitals (except z2) all at a lower energy level (not seen).