1. A method of modeling at least one physical property of a mixture of at least two chemical species using a modeler, the method comprising the computer implemented steps of: a) providing a computer programmed to serve as a modeler, the modeler during execution being formed of (i) a databank of molecular descriptors of known chemical species, and (ii) a calculator of molecular descriptors of unknown chemical species, the modeler being configured to be executable by a processor; b) determining at least one conceptual segment, instead of a molecular structural segment, for each of the at least two chemical species, the conceptual segment being determined from in-mixture behavior of the at least two chemical species, including for each conceptual segment, (i) identifying the conceptual segment as one of a hydrophobic segment, a hydrophilic segment, a polar segment, or a combination thereof, and (ii) defining an equivalent number for the conceptual segment, the equivalent number being based on experimental phase equilibrium data and being one of carried in the databank of molecular descriptors of known chemical species or obtained using the calculator of molecular descriptors of unknown chemical species by regression of experimental phase equilibrium data for binary systems of unknown chemical species and reference chemical species; c) providing the determined at least one conceptual segment to the modeler, and in response the modeler using the determined at least one conceptual segment to compute at least one physical property of the mixture, including any one of vapor pressure, solubility, boiling point, freezing point, octanol/water partition coefficient, or a combination thereof, the modeler computing the at least one physical property by determining an activity coefficient of one of the at least two chemical species, the activity coefficient being formed of at least a residual contribution to the activity coefficient of the one chemical species, the modeler setting the residual contribution equal to a local composition interaction contribution to the activity coefficient for the one chemical species based on the determined at least one conceptual segment; d) analyzing the computed at least one physical property using the modeler, in a comparison to the computed at least one physical property of other mixtures of at least two chemical species, and forming therefrom a model of the at least one physical property of the mixture; and e) outputting the formed model from the modeler to a computer display monitor.