Atomic Radius: The atomic radius is the size of the atom of an element. The values decrease. Yes, they both decrease. The atomic radius increases. Yes, but they increase at a slower rate. Ionic Radius: An atom becomes a cation when an atom loses electrons in a reaction. An atom becomes an anion when it gains electrons in a reaction. The cations? values decrease. The anion?s values also decrease. Yes, their trends are the same. The ionic radius value increases. Yes, they also increase. Electronegativity: Electronegativity is the measurement of an element?s tendency to react with electrons in a chemical bond. The values greatly increase. Yes, they both increase. The values slowly decrease. No, because only one number in group 18 is plotted.