Covalent radii from ionization energies of isoelectronic series

Slater’s covalent radii agree nicely with experiment when the effective principal quantum number and the screening constant for the outermost electron are taken from fits of the hydrogen-like energy level expression to ionization energies in isoelectronic series. This establishes a simple connection between the two prominent periodic properties of atoms, namely, their radius and (effective) ionization energy.