Additivity of intermolecular forces

Theoretical considerations based upon a molecular approach to solvation are not yet very sophisticated. As in the case of ionic solvation, but even more markedly, the connection between properties of liquid mixtures and models on the level of molecular colculations is, despite all the progress made, an essentially unsolved problem. Even very crude approximative approaches utilizing for example the concept of pairwise additivity of intermolecular forces are not yet tractable, simply because extended potential hypersurfaces of dimeric molecular associations are lacking. A complete hypersurface describing the potential of two diatomics has already a dimensionality of six In this light, it is clear that advanced calculations are limited to very basic aspects of intermolecular interactions,... 

Subsequently, a kinetic theory of intercollisional interference was developed (Lewis 1980 and 1985). The kinetic theory was based on the idea of pairwise additivity of intermolecular force and induced dipole moment. It traces the collisional history of an individual molecule of a highly diluted system. The traced molecule may be a vibrating molecule, surrounded by non-vibrating molecules, or else a dissimilar molecule of low concentration (gas mixtures). 

Fowkes FM. (1963). Additivity of intermolecular forces at interfaces. L Determination of the contribution to surface and interfacial tensions of dispersion forces in various liquids. / Phys Chem 67 2538-2541. 

Surface tensions, interfacial tensions, and contact angles can be used as laboratory tools for the evaluation of the various intermolecular forces that determine cohesion in a single phase or adhesion between two dissimilar materials at an interface. By the use of these tools, considerable information about the magnitude of various intermolecular forces may become available. Basic understanding of means to determine interfacial forces has sprung from the principle of additivity of intermolecular forces at surfaces and interfaces [4, 6]. 

The term polymer is derived from the Greek words poly and meros, meaning many parts. We noted in the last section that the existence of these parts was acknowledged before the nature of the interaction which held them together was known. Today we realize that ordinary covalent bonds are the intramolecular forces which keep the polymer molecule intact. In addition, the usual type of intermolecular forces—hydrogen bonds, dipole-dipole interactions, and London forces—hold assemblies of these molecules together in the bulk state. The only thing that is remarkable about these molecules is their size, but that feature is remarkable indeed. 

The dispersion forces in acetone are nearly the same as those in 2-methylpropane, but the addition of dipolar forces makes the total amount of intermolecular attraction between acetone molecules substantially greater than the attraction between molecules of 2-methylpropane. Consequently, acetone boils at a considerably higher... 

Molecules in contact with the surface of their container experience two sets of intermolecular forces. Cohesive forces attract molecules in the liquid to one another. In addition, adhesive forces attract molecules in the liquid to the molecules of the container walls. 

C12-0058. A rise in temperature accompanies the addition of water to a concentrated solution of HCl. Explain this phenomenon in terms of intermolecular forces. 

In addition to the contribution of intermolecular forces, chain entanglement is also an important contributory factor to the physical properties of polymers. While paraffin wax and HDPE are homologs with relatively high molecular weights, the chain length of paraffin is too short to permit chain entanglement, and hence lacks the strength and other characteristic properties of HDPE. 

Intermolecular forces, known collectively as van der Waals forces, are the attractions responsible for holding particles together in the liquid and solid phases. There are several kinds of intermolecular forces, all of which arise from electrical attractions Dipole-dipole forces occur between two polar molecules. London dispersion forces are characteristic of all molecules and result from the presence of temporary dipole moments caused by momentarily unsymmetrical electron distributions. A hydrogen bond is the attraction between a positively polarized hydrogen atom bonded to O, N, or F and a lone pair of electrons on an O, N, or F atom of another molecule. In addition, ion-dipole forces occur between an ion and a polar molecule. 

Surface energy is a direct manifestation of intermolecular forces. The molecules at the surface of a liquid or a solid are influenced by unbalanced molecular forces and therefore possess additional energy, in contrast with the molecules inside the liquid or solid. 

The key requirements of a fiber are, then, a molecular shape—linear—that permits side-by-side alignment, and strong intermolecular forces to maintain this alignment. In addition, the intermolecular forces prevent slipping of one molecule past another. Now, what are these intermolecular forces ... 

In addition to intermolecular forces, yet another consideration determines whether a given solute dissolves in a particular SCF solvent—the free volume difference between the mixture components. By free volume we essentially mean the expansivity of a substance, or inversely, its compressibility. The key question is whether the molecules in solution are within close enough proximity to interact. Statistical thermodynamics provides us with the equations that... 

Since cw-dichloroethylene is a polar molecule but fran -dichloroethylene is not, they can readily be distinguished by a dipole moment measurement. Additionally, as we will see in the next chapter, the strength of intermolecular forces is partially determined by whether molecules possess a dipole moment. Table 10.3 lists the dipole moments of several polar molecules. 

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