Force molecular attraction

The data for at, collected in Tables 5-8, show that at appears to decrease exponentially with n. This is consistent with the point of view that a reflects the dynamic packing density of the sorbed molecules with respect to the adsorption site, namely the styrene units in poIy(Sty-co-DVB), i.e. it reflects the net result of two opposing forces molecular attraction and the reactionary force of steric hindrance [from the standpoint of space limitation at the available adsorption site]. The difference in these opposing forces affect the rates of adsorption and desorption exponentially, which should decrease incrementally with n, and therefore Log acn should be a linear function of n as given by ... 

The extremely nonpolar character of PFCs and very low forces of attraction between PFC molecules account for their special properties. Perfluorocarbons bod only slightly higher than noble gases of similar molecular weight, and their solvent properties are much more like those of argon and krypton than hydrocarbons (2). The physical properties of some PFCs are Hsted in Table 1. 

Acetate fibers are dyed usually with disperse dyes specially synthesized for these fibers. They tend to have lower molecular size (low and medium energy dyes) and contain polar groups presumably to enhance the forces of attraction by hydrogen bonding with the numerous potential sites in the cellulose acetate polymer (see Fibers cellulose esters). Other dyes can be appHed to acetates such as acid dyes with selected solvents, and azoic or ingrain dyes can be apphed especially for black colorants. However thek use is very limited. 

It must be pointed out that deviations from such a simple relationship do occur. For example, since random copolymerisation tends to promote disorder, reduce molecular packing and also reduce the interchain forces of attraction, the Tg of copolymers is often lower than would be predicted by the linear relationship. Examples are also known where the Tg of the copolymer is higher than predicted. This could occur where hydrogen bonding or dipole attraction is possible between dissimilar comonomer residues in the chain but not between similar residues, i.e. special interchain forces exist with the copolymers. 

A chemical will be a solvent for another material if the molecules of the two materials are compatible, i.e. they can co-exist on the molecular scale and there is no tendency to separate. This statement does not indicate the speed at which solution may take place since this will depend on additional considerations such as the molecular size of the potential solvent and the temperature. Molecules of two different species will be able to co-exist if the force of attraction between different molecules is not less than the forces of attraction between two like molecules of either species. If the average force of attraction between dissimilar molecules A and B is and that between similar molecules of type B Fbb and between similar molecules of type A F a then for compatibility Fab - bb and AB - P/KA- This is shown schematically in Figure 5.5 (a). 

Adsorption on solids is a process in which molecules in a fluid phase are concentrated by molecular attraction at the interface with a solid. The attraction arises from van der Waals forces, which are physical interactions between the electronic fields of molecules, and which also lead to such behavior as condensation. Attraction to the surface is etihanced because the foreign molecules tend to satisfy an imbalance of forces on the atoms in the surface of a solid compared to atoms within the solid where they are surrounded by atoms of the... 

If we had any means of reducing the electrostatic repulsion without, at the same time, affecting the quantum-mechanical attraction, we should have the possibility of forming such doubly charged molecular ions. Now a polar solvent has just the required properties the alignment of the solvent dipoles greatly reduces the electrostatic repulsion, but the quantum-mechanical forces of attraction arise from the rapid motion of... 

Properties of Different Solvents. In discussing molecular dipoles in Sec. 25, we estimated the force of attraction between an atomic ion and a dipole having the most favorable orientation and found this attraction to be very strong. In any ionic co-sphere those molecular dipoles which have a favorable orientation will bo attracted, while those that have the opposite orientation will be repelled. Since the former are more numerous the solvent in the co-sphere is, on the whole, attracted toward the ion. Since the liquid is not incompressible, we must expect that this will lead to a contraction in each co-sphere. In any ionic solution the sum of the contractions that have taken place in the co-spheres of the positive and negative ions will be apparent if we measure accurately the volume of the solution. 

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. 

A gas condenses to a liquid if it is cooled sufficiently. Condensation occurs when the average kinetic energy of motion of molecules falls below the value needed for the molecules to move about independently. Thus, the molecules in a liquid are confined to a specific volume by intermolecular forces of attraction. Although they cannot readily escape, liquid molecules remain free to move about within the liquid phase, hi this behavior, liquid molecules behave like the molecules of a gas. The large-scale consequences of the molecular-level properties are apparent. Like gases, liquids are fluid, so they flow easily from place to place. Unlike gases, however, liquids are compact, so they cannot expand or contract significantly. 

Molecular attraction (surface tension, adsorptive, diffusive, and osmotic forces)... 

This expression applies to the transport of any conserved quantity Q, e.g., mass, energy, momentum, or charge. The rate of transport of Q per unit area normal to the direction of transport is called the flux of Q. This transport equation can be applied on a microscopic or molecular scale to a stationary medium or a fluid in laminar flow, in which the mechanism for the transport of Q is the intermolecular forces of attraction between molecules or groups of molecules. It also applies to fluids in turbulent flow, on a turbulent convective scale, in which the mechanism for transport is the result of the motion of turbulent eddies in the fluid that move in three directions and carry Q with them. 

Dispersion forces are the only important intermolecular forces of attraction operating between the nonpolar molecules of (a) molecular AlBr3 and (b) PC15. 

There are similarities between the intermolecular attractions used to describe on a molecular level (1) viscosity, (2) surface tension, (3) the rate of evaporation and resulting vapor pressure of a liquid. For compounds in the liquid phase that have strong intermolecular forces of attraction operating between its molecules ... 

In nature, the halogens exist as nonpolar diatomic molecules. London dispersion forces are the only forces of attraction acting between the molecules. These forces increase with increasing molecular size. 

Ionic compounds are made up of positively charged ions (usually metal ions) and negatively charged ions (usually non-metal ions or polyatomic anions) held together by electrostatic forces of attraction. Molecular compounds are made up of discrete units called molecules. Generally they consist of a small number of nonmetal atoms held together by covalent bonds (sharing of electrons). 

To connect the internal latent heat with the intrinsic pressure let us consider the forces to which a molecule of the liquid is subject. As long as it is in the interior of the liquid these are obviously equal in all directions, but the case is different when the molecule approaches the surface nearer than the radius of molecular attraction. Let O (Fig. 4) be such a molecule and describe round it a sphere with the radius C of molecular attraction then only the liquid within that sphere will have any effect on O. In the position shown the molecule is attracted downwards by the liquid contained in the segment ab (equal to AB), as the downward... 

LlFSHITZ, E. M. Soviet Physics. J.E.T.P. 2 (1956) 73. Theory of molecular attractive forces between solids. 

At distances greater than a few molecular diameters, the energy of attraction is negligible. As the molecules approach, the force of attraction increases (the potential energy decreases) as natural or induced dipoles begin to interact. As... 

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