A simple model for the interaction of the solute with the solvent is presented. The relation between the molecular volume, partial molar volume, and the volume of the solvation shell of the compound studied is expressed by the α parameter, defined as the relative density of the solvation shell. The values of α are calculated for many organic compounds in aqueous solutions. It is stated that in a given series of compounds, α depends strongly on the number of CH2 groups in the compound studied. The correlation of α and the polarity (defined as the ratio of the surface area of polar groups and atoms exposed to the total molecular surface area of the molecule studied) was found.