Forces between molecules electrostatic

Many of the other important attractive forces between molecules can be explained in terms of electrostatics. The simplest such force leads to an attractive energy of interaction between spherically symmetrical monovalent ions of unlike sign given by the familiar expression... 

In addition to this universal repulsive force, there are also important attractive forces between molecules if they are charged. Cations (+) and anions (-) attract each other electrostatically and this may be enough for reaction to occur. When an alkyl chloride, RCl, reacts with sodium iodide, NaT, in acetone (propanone, Me2C=0) solution a precipitate of sodium chloride forms. Sodium ions, Na+, and chloride ions, Cl-, ions in solution are attracted by their charges and combine to form a crystalline lattice of alternating cations and anions—the precipitate of crystalline sodium chloride. 

All the important contributions to the forces between molecules arise ultimately from the electrostatic interactions between the particles that make up the two molecules. Thus our main theoretical insight into the nature of intermolecular forces comes from perturbation theory, using these interactions as the perturbation operator H = Z e, /(4jtSor/y), where is the charge on particle i in one molecule, is the distance between particles i and / in different molecules, and 8q is permittivity of a vacuum. The definitions of the contributions, such as the repulsion, dispersion, and electrostatic terms, which are normally included in model potentials, correspond to different terms in the perturbation series expansion. 

Interpreting bulk properties qualitatively on the basis of microscopic properties requires only consideration of the long-range attractive forces and short-range repulsive forces between molecules it is not necessary to take into account the details of molecular shapes. We have already shown one kind of potential that describes these intermolecular forces, the Lennard-Jones 6-12 potential used in Section 9.7 to obtain corrections to the ideal gas law. In Section 10.2, we discuss a variety of intermolecular forces, most of which are derived from electrostatic (Coulomb) interactions, but which are expressed as a hierarchy of approximations to exact electrostatic calculations for these complex systems. 

Parallel to these studies, the study of real gases had led to the introduction of interaction forces between molecules, responsible for the differences between real fluids and perfect gases. These forces could be attributed to an electrostatic origin dipole force, polarization and orientation effects 2 >. 

Most organic species form molecular crystals in which discrete molecules are arranged in fixed positions relative to the lattice points. This of course means that the individual atoms making up the molecules are each arranged at fixed positions relative to each other, the lattice point, and the other molecules. The forces between molecules in molecular crystals are generally weak when compared with the forces within a molecule. The structure of molecular crystals is affected by both the intermolecular forces and the intramolecular forces since the shapes of the individual molecules will affect the way the molecules pack together. In addition, the properties of the individual molecule, such as the polarity, will affect the intermolecular forces. The forces between the molecules in molecular crystals include electrostatic interactions between dipoles, dispersion forces, and hydrogen bond... 

Because of the large number of configurations sampled the authors restricted themselves to empirical force fields for computing the intermolecular energies. This is not only faster than a quantum-based approach but it is better because empirical force fields reproduce more accurately the dispersion forces between molecules than do quantum methods at a Hartree-Fock level of theory. Because empirical force fields are not particularly accurate or precise, the authors decided to treat the R and S analytes in an identical manner as explained above. This way, if the force field underestimates, say, hydrogen bonding and overestimates electrostatics, the errors should be nearly the same for both R and S analytes. This cancellation of errors... 

A molecule has many charges in it, and they are distributed in a complex way, as governed by the quantum-mechanical state of the molecule. In general there is much more information about the electrostatic properties of the molecule than is contained in its dipole moment. However, at distances far from the molecule (as compared to the molecule s size), these details do not matter. The forces that one molecule exerts on another in this limit are strongly dominated by the dipole moments of the two molecules. In this limit, too, the details of the dipole moment s origin are irrelevant, and we consider the molecule to be a point dipole, with a dipole moment characterized by a magnitude p, and a direction i. We consider in this chapter only electrically neutral molecules, so that the Coulomb force between molecules is absent. 

Produced by the above means, probabiy in a confidential scheme, the activated carbon must have the following characteristics (1) adequate mesopores (cavities) which constitute pathways for iarge and small molecules to access the inner porous structure, (2) a surfeit of micropores (less than 2 nm in major diameter) which contain the primary adsorption sites, and (3) nearly complete modification of the internal surface structure to make it capable of attracting and bonding to chemicals via van der Waals forces (weak electrostatic forces between molecules), not the covalent or ionic forces bonding the atoms of molecules together. 

For crystallographically non-equivalent atoms the corresponding components of the electric field gradient (EFG) at the respective sites differ from each other in magnitude and direction due to the crystal field effect. This generally includes a contribution to the EFG of electrostatic forces between molecules, dispersion forces, intermolecular bonding and short-range repulsion forces. Physically non-equivalent sites differ from each other only in the direction of... 

In physical chemistry, the van der Waals force (or van der Waals interaction), named after Dutch scientist Johannes Diderik van der Waals, is the sum of the attractive or repulsive forces between molecules (or between parts of the same molecule) other than those due to covalent bonds or to the electrostatic interaction of ions with one another or with neutral molecules. The term includes the force between two permanent dipoles (Keesom force), the force between a permanent dipole and a corresponding induced dipole (Debye force) and the force between two instantaneously induced dipoles (London dispersion force) It is also sometimes used loosely as a s5monym for the totality of intermo-... 

Unlike the forces between ions which are electrostatic and without direction, covalent bonds are directed in space. For a simple molecule or covalently bonded ion made up of typical elements the shape is nearly always decided by the number of bonding electron pairs and the number of lone pairs (pairs of electrons not involved in bonding) around the central metal atom, which arrange themselves so as to be as far apart as possible because of electrostatic repulsion between the electron pairs. Table 2.8 shows the essential shape assumed by simple molecules or ions with one central atom X. Carbon is able to form a great many covalently bonded compounds in which there are chains of carbon atoms linked by single covalent bonds. In each case where the carbon atoms are joined to four other atoms the essential orientation around each carbon atom is tetrahedral. 

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