We propose it new definition of the effective radius of all atomic ion the bond distance (R-e) of the ion/He diatomic complex minus the van der Waals radius of the helium atom Our rationale is that He is the most chemically inert and least polarizable atom. so that Its Interaction With the outer portions of the electron cloud causes the smallest perturbation of it We show that such radii, which we denote R-XHe, make good qualitative sense. We also compare our R-XHe values to more traditional ionic radii from solid crystal X-ray measurements, as well as estimates Of such radii from "ionic" gas-phase MF, MOM, MF+, and MO molecules, where M is a metal atom Such comparisons lead to interesting conclusions about bonding ill ionic crystals and in simple gas-phase oxide and fluoride molecules The definition is shown to be reasonable for -1, +1, and even for many of file larger +2 atomic ions. Another advantage of the R-XHe definition is that it is also consistently valid for ground states and excited states of both neutral atoms and atomic Ions, even for open-shell np and nd cases where the electron clouds of the ions ire not spherically symmetric and R-XHe thus depends oil the "approach" direction of the He atom. Finally, we note that when there is a contribution from covalent bonding with the He atom, and/or in cases where the ion is small and has very high charge, so that there is distortion even of the He Is electrons. R-XHe is not expected to be representative of the size of the ion. We then Suggest that ill these cases small, and sometimes unphysical, values of R-XHe are diagnostic of the Fact that Simple "physical" interactions have been supplemented by a "chemical" component.