Explain the following variations in atomic or ionic radii: Fe>Fe2 >Fe3 1. The 4s valence electrons in Fe are on average from the nucleus than the 3d electrons, so Fe is larger than Fe2 . 2. Because there are five 3d orbitals, in Fe2 at least must contain a pair of electrons. 3. Removing one electron to form Fe3 significantly repulsion, increasing the nuclear charge experienced by each of the other d electrons and decreasing the size of the ion.