Upon oxidation of an atom, what occurs to the radius of the resultant cation compared to the parent atom?
The radius of the resultant cation should diminish markedly.
The electron is lost from a valence shell, and, for the alkali metals, there is only the one electron occupying the valence shell. Here, the radius of the ion is stripped back to the next shell. Not only is the valence electron attracted to the positively charge nuclear core, but electron-electron repulsion is diminished.
But as chemists, as physical scientists, we should always seek the data that inform our argument. See this [site.] Units are in Angstroms,