Origin of attractions

In the next section we consider the molecular origins of attractions between colloidal particles. 

See also Footnote 9 (Sect. 1.3) for an alternative discussion of the origin of attractive interactions between fluorinated and non-fluorinated aromatics. 

The reader will learn abont the origins of attractive forces between particles and how to overcome these forces, yielding a dispersed system. Furthermore, it is shown how these interparticle forces relate to the flow behavior of the slurry system, and finally, how this knowledge can be applied to current direct casting techniques. 

The origin of attractive intermolecular interactions and the factors determining the geometry of molecular complexes is still being sought after decades of numerous experimental and theoretical techniques. The interaction energy, AE, is the difference between the energy of the species AB and the two isolated molecules A and... 

Tsuzuki, S., Honda, K., Uchimaru, T, Mikami, M., and Tanabe, K. [2002]. Origin of attraction and directionality of the n-n interaction Model chemistry calculations of benzene dimer interaction,/ Am. Chem. Soc. 124,1, pp. 104-112. 

Origin of Attraction and Directionality of the n-n Interaction Model Chemistry Calculations of Benzene Dimer Interaction. 

Until surface contact, the force between molecules is always one of attraction, although this attraction has different origins in different systems. London forces, dipole-dipole attractions, acid-base interactions, and hydrogen bonds are some of the types of attraction we have in mind. In the foregoing list, London forces are universal and also the weakest of the attractions listed. The interactions increase in strength and also in specificity in the order listed. 

As argued above, this result is found to work best for substances in which both the 1,1 and 2,2 forces are either London or dipole-dipole. Even the case of one molecule with a permanent dipole moment interacting with a molecule which has only polarizability and no permanent dipole moment-such species interact by permanent dipole-induced dipole attraction-is not satisfactorily approximated by Eq. (8.46). In this context the like dissolves like rule means like with respect to the origin of intermolecular forces. 

Now let us examine the molecular origin of Molecular polarity may be the result of either a permanent dipole moment p or an induced dipole moment ind here the latter arises from the distortion of the charge distribution in a molecule due to an electric field. We saw in Chap. 8 that each of these types of polarity are sources of intermolecular attraction. In the present discussion we assume that no permanent dipoles are present and note that the induced dipole moment is proportional to the net field strength at the molecule ... 

The most common type of intermolecular force, found in all molecular substances, is referred to as a dispersion force. It is basically electrical in nature, involving an attraction between temporary or induced dipoles in adjacent molecules. To understand the origin of dispersion forces, consider Figure 9.8. 

The simplest state of matter is a gas. We can understand many of the bulk properties of a gas—its pressure, for instance—in terms of the kinetic model introduced in Chapter 4, in which the molecules do not interact with one another except during collisions. We have also seen that this model can be improved and used to explain the properties of real gases, by taking into account the fact that molecules do in fact attract and repel one another. But what is the origin of these attractive and... 

Before leaving the subject of distribution of electrons within molecules, and its attribution to the origin of molecular polarity, with consequent effect on intermolec-ular forces (with further consequent effects on solubilities and melting points), it is pertinent to remind ourselves of two significant challenges faced by chemistiy instractors (i) to graphically represent forces of attraction between molecules and (ii) to develop the imagery that in the liquid state, orientation of molecules toward each other because of polarities is transitory, even if more probable, as they move past each other. 

The free electron resides in a quantized energy well, defined by k (in wave-numbers). This result Ccm be derived from the Schroedinger wave-equation. However, in the presence of a periodic array of electromagnetic potentials arising from the atoms confined in a crystalline lattice, the energies of the electrons from all of the atoms are severely limited in orbit and are restricted to specific allowed energy bands. This potential originates from attraction and repulsion of the electron clouds from the periodic array of atoms in the structure. Solutions to this problem were... 

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