We employ the Slater-Zener model to relate effective atomic radius to ionization energy: r(e) = na(0)root I-H/(I) over bar (v;) n is the principal quantum number of the valence shell, a(0) is the Bohr radius, I-H is the ionization energy of the hydrogen atom, and (I) over bar (v) is the average valence ionization energy. Along a given row in the periodic table, these semi-empirical radii correlate linearly with theoretical Hartree-Fock radii, semi-empirical radii derived from static dipole polarizability, and empirical covalent radii. Correlation of radii column by column is not as accurate, but still respectable. The asymptotic electron density varies as exp(-2 root 2 (I) over bar (v)r), which reverts to exp(-2 root 2 (I) over bar (0)r) upon invoking the frozen orbital approximation. (C) 2012 Elsevier B.V. All rights reserved.