 in the sequence RI>RBr>RCl>RF.In absence of solvents weakly polarizable hydrocarbons form due to dispersive forces crystals; their sublimation heat is a measure of the dispersive interaction.For macroscopic bodies with known volumes and numbers of atoms or molecules per unit volume, the total van der Waals force is often computed based on the "microscopic theory" as the sum over all interacting pairs.