Intermolecular attraction, forces

Induced dipole/induced dipole forces are the only intermolecular attractive forces available to nonpolar molecules such as alkanes In addition to these forces polar molecules engage m dipole-dipole and dipole/mduced dipole attractions The dipole-dipole attractive force is easiest to visualize and is illustrated m Figure 4 3 Two molecules of a polar substance experience a mutual attraction between the positively polarized region of one molecule and the negatively polarized region of the other As its name implies the dipole/induced dipole force combines features of both the induced dipole/mduced dipole and dipole-dipole attractive forces A polar region of one mole cule alters the electron distribution m a nonpolar region of another m a direction that produces an attractive force between them... 

Because so many factors contribute to the net intermolecular attractive force it is not always possible to predict which of two compounds will have the higher boiling point We can however use the boiling point behavior of selected molecules to inform us of the relative importance of various intermolecular forces and the structural features that influence them... 

A substance exists as a liquid rather than a gas because attractive forces between molecules (intermolecular attractive forces) are greater in the liquid than in the gas phase. Attractive forces between neutral species (atoms or molecules, but not ions) are referred to as van der Waals forces and may be of three types ... 

The melting points and boiling points of car boxylic acids are higher than those of hydro-carbons and oxygen-containing organic compounds of comparable size and shape and indicate strong intermolecular- attractive forces. 

The magnitude of this effect depends on the strength of the attractive forces and hence on the nature of the gas. Intermolecular attractive forces are stronger in C02 than they are in 02, which explains why the deviation from ideality of Vmis greater with carbon dioxide and why carbon dioxide is more readily condensed to a liquid than is oxygen. 

Boiling point and melting point would be expected to be comparable because they both are functions of the strength of intermolecular attractive forces. 

The term polarity refers to the ability of a sample or solvent molecule to interact by combination of dispersion, dipole, hydrogen bonding, and dielectric interactions (see Chapter 2 in reference 5). The combination of these four intermolecular attractive forces constitutes the solvent polarity, which is a measure of the strength of the solvent. Solvent strength increases with polarity in normal phase, and adsorption HPLC decreases with polarity in reversed-phase HPLC. Thus, polar solvents preferentially attract and dissolve polar solute molecules. 

Due to the neighbourhood of secondary alcohol groups and remaining hydro-phobic acetyl groups in a not fully hydrolysed polymer, a balanced situation results that dictates the overall water solubility. Temperature plays an important role in that interplay between the intermolecular attracting forces and the polymer water interaction. An optimum in cold water solubility can be observed with a DH of 87-89 mol% for molecular weights between 25,000 and 100,000 Da (degree of polymerisation, DP, 600-2,400). 

Cohesion intermolecular attractive force between particles within a substance Colligative Property a property dependent on the number of particles in solution and not on the type of particles, for example, boiling point elevation and freezing point depression... 

The first thermodynamic expression above states that the intermolecular attraction forces we must overcome to sublime the molecules of a substance are equal to the sum of the forces required to first melt it and then vaporize it. Likewise, the increased randomness obtained as molecules sublime is the same as the sum of entropies associated with the sequence of melting and vaporizing. Consequently, if we can predict such thermodynamic terms for vaporization or melting, we already know the corresponding parameters for sublimation. 

Extended assemblies of induced-dipole/induced-dipole attractions can accumulate to give substantial intermolecular attractive forces. An alkane with a higher molecular... 

The intermolecular attractive force due to hydrogen bonding is greater between alcohols than it is between amines because of the greater polarity of an O-H bond compared with an N-H bond. 

In linear polymers, cohesion results from weak (compared with covalent bonds) intermolecular attractive forces (Van der Waals) of various types London, Debye, Keesom, and hydrogen bonding. In a first approach, they can be considered undistinguishable, and one can define cohesive energy as the whole energy of intermolecular interactions. For small molecules, cohesive energy is easy to determine from calorimetric measurements since... 

Because unbranched alkanes are neutral, nonpolar molecules, it is difficult to explain the existing intermolecular force between such alkanes that increases as the alkane molecules become larger. We will see that this attractive force is weak and tenuous. These molecules do not become overly friendly with each other. In theory, as atoms within one alkane molecule approach the atoms of another alkane molecule, the electrons around these atoms, for an instant, arrange themselves asymmetrically around the atoms so that instant dipoles are formed—the positive side of one atom attracts the negative side of another atom. This weak intermolecular attractive force is called a London Force. When there is a weak intermolecular attractive force between polar molecules, the force is called a dipole-dipole force. Together, London forces and dipole-dipole forces are called Van der Waals forces. 

This results in large impact parameters and cross sections where A is still at large distances when BC splits. The intermolecular attractive forces between A and B must be strong. 

As the science of adhesion has developed, various theories of adhesion have been advocated for one material or another. With wood as a substrate, mechanical interlocking, interdiffusion of polymers, intermolecular attractive forces, and covalent chemical bonding all have been proposed, either individually or collectively, to explain adhesion. In reality, no experiments reported to date have been able to disprove the existence of any one of these mechanisms, or to quantify their relative importance. A most exasperating feature of research on adhesion to wood is that factors presumed to be independent in experiments are never totally independent. 

Molecules have kinetic energy (they move around), and they also have intermolecular attractive forces (they stick to each other). The relationship between these two determines whether a collection of molecules will be a gas, liquid, or solid. 

In a solid, the energy of intermolecular attractive forces is much stronger than the kinetic energy of the molecules, so kinetic energy and kinetic molecular theory are not very important. As temperature increases in a solid, the vibrations of individual molecules grow more intense and the molecules spread slightly further apart, decreasing the density of the solid. 

In a liquid, the energy of intermolecular attractive forces is about as strong as the kinetic energy of the molecules and both play a role in the properties of liquids. 

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