Attractive forces between molecules

The capillary effect is apparent whenever two non-miscible fluids are in contact, and is a result of the interaction of attractive forces between molecules in the two liquids (surface tension effects), and between the fluids and the solid surface (wettability effects). 

A substance exists as a liquid rather than a gas because attractive forces between molecules (mtermolecular attractive forces) are greater m the liquid than m 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... 

In general aldehydes and ketones have higher boiling points than alkenes because they are more polar and the dipole-dipole attractive forces between molecules are stronger But they have lower boiling points than alcohols because unlike alcohols two carbonyl groups can t form hydrogen bonds to each other... 

The molecules of liquids are separated by relatively small distances so the attractive forces between molecules tend to hold firm within a definite volume at fixed temperature. Molecular forces also result in tlie phenomenon of interfacial tension. The repulsive forces between molecules exert a sufficiently powerful influence that volume changes caused by pressure changes can be neglected i.e. liquids are incompressible. 

Hydrogen bond An attractive force between molecules found when a hydrogen atom is bonded to N, O, or F, 238-240, 616... 

For liquids, as the temperature increases, the degree of molecular motion increases, reducing the short-range attractive forces between molecules and lowering the viscosity. The viscosity of various liquids is shown as a function of temperature in Appendix A. For many liquids, this temperature dependence can be represented reasonably well by the Arrhenius equation ... 

Therefore, attractive forces between molecules decrease as one moves up the group, resulting in lower melting points... 

Drawing a Conclusion Based on your data, in which liquid(s) are the attractive forces between molecules most likely to be dispersion forces ... 

Van der Waals equation is (p + a/F2) (F — 6) = RT, where p is the pressure, F the molar volume, T the absolute temperature, a the Van der Waals constant to account for attractive forces between molecules, and b the Van der Waals constant to account for the finite volume of molecules. 

The heat energy required to convert 1,0 g of a liquid at its boiling point, at atmospheric pressure, into its gaseous state at the same temperature. It is a direct measure of the energy required to overcome attractive forces between molecules in the liquid phase. 

Cohesive force An attractive force between molecules of the same substance. 

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... 

Just as shape is a common and essential element in the construction of a sculpture, the shape of a molecule is extremely important in determining the physical and chemical properties of a substance. For the alkanes, as the number of carbon atoms in the molecule increases, thereby increasing the molecular weight, the boiling point and the melting point of the substances increase. This would indicate that intermolecular forces, the attractive forces between molecules, increase as the number of carbon atoms and the molecular weight of the alkane molecules increase. 

Figure 4.1 Attractive forces between molecules at the surface and in the interior of a liquid...

Prediction 2, that such big molecules ought to be supercritical gases under ambient conditions, is supported by a more contentious argument based on their equation of state. The liquid state, and condensed phases in general, exist because of the short-range attractive forces between molecules. The simplest of all equations of state, Boyle s Law, PV = RT, makes no provision for attractive forces and does not predict condensed phases. The next approximation is Van der Waals equation ... 

Solubility Parameter. Increased attractive forces between molecules, as measured by a larger solubility parameter, requires more thermal energy to produce molecular motion. This results in an increase in the Tg with increasing cp. Eisenberg (1993) provides an equation that relates the molar cohesive energy density,o2p, to the glass transition by... 

As seen in Fig. 4, the attractive forces between molecules are weaker, but much longer range than the repulsive forces.8 To find the form of the contribution from the attractive forces to the pressure, van der Waals noted that pressure results from collisions between molecules and the walls of the container. For a molecule colliding with a wall, attractive forces between molecules would result in a force directed toward other molecules in the container and away from the wall. The attractive forces thus result in a reduction in pressure. For any one molecule colliding with the wall, the pressure reduction should be proportional to the density of molecules pulling it back into the gas during collision (N/ V). However, the rate at which molecules collide with the walls is also proportional... 

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