A link between the ionization energy ratios of an atom and its electronegativity and hardness

We explain the earlier observation that Taylor series expansions of atomic energies essentially terminate after the second-order term if the atoms’ ionization energies obey In = n(I1). Our analysis provides some support for the validity of the widely-used electronegativity and hardness formulas 0.5(I + A) and 0.5(I−A), for the atoms in Groups IIA and IVA – VIIIA, oxygen being an exception.