  An extended Designed regression analysis of experimental data on density and
refractive indices of several classes of ionic liquids yielded statistically
averaged atomic volumes and polarizabilities of the constituting atoms. These
values can be used to predict the molecular volume and polarizability of an
unknown ionic liquid as well as its mass density and refractive index. Our
approach does not need information on the molecular structure of the ionic
liquid, but it turned out that the discrimination of the hybridization state of
the carbons improved the overall result. Our results are not only compared to
experimental data but also to quantum-chemical calculations. Furthermore,
fractional charges of ionic liquid ions and their relation to polarizability
are discussed.
