2px 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 orbital is transparent at middle to show axes of symmetry. A planar node normal to the axis of the orbital can be seen at right. Nodes are the regions an atom with zero electron density and where the electron is least likely to exist. The 2px electron orbital is named as such because the 2 corresponds to the second energy level, p indicates that the orbital is shaped like a dumbbell shape with two lobes, and x indicates the orientation of the orbital along the x-axis. The 2p orbitals belong to the 2 shell, which also contains a lower-energy 2s orbital that is spherical in shape. In atoms, electrons fill the lower energy orbitals first. The 2s orbital is only filled when the lowest energy 1s orbital is full, and the 2p orbital is only filled when both 1s and 2s are full. The 1s and 2s orbitals can both hold a pair of electrons each, as can each 2p orbital. The 2p orbitals are thus full in element 10, neon. Neons electron configuration is written 1s2 2s2 2p6.