Final answer:
The 'rf values' mentioned seem to refer mistakenly to concepts related to isoelectronic ions and their sizes, not chromatography. In isoelectronic series, ions have the same electron configuration but different number of protons, affecting their ionic sizes. More protons result in a greater nuclear charge and a smaller ionic radius.
Step-by-step explanation:
When we talk about rf values, we're often discussing a concept in chromatography, which relates to how far a compound travels on a chromatogram. However, the context provided here appears to relate more closely to ionic radii and electron configurations. Based on this information, rf values in the context provided may be a typo or misuse of terminology, as the question seems to revolve around isoelectronic series and ionic radii rather than chromatography.
Atoms and ions that have the same electron configuration are said to be isoelectronic. In a series of isoelectronic ions, while the number of electrons remains constant, the number of protons will vary. This variation in the number of protons -- and thus the nuclear charge -- results in differences in ionic size. The greater the nuclear charge within a series of isoelectronic species, the more attraction the nucleus exerts on the electrons, which leads to a smaller ionic radius.
This concept is important for understanding trends in the periodic table, such as why ions in a vertical column have increasing size as you move down the column due to additional electron shells being added that outweigh the increase in nuclear charge, thus the ionic radii increase. But for isoelectronic ions, as the number of protons increases, the ionic size decreases because of the greater nuclear charge pulling the electrons closer to the nucleus, leading to a smaller ionic radius.