Intermolecular forces induced dipoles

Attractive or repulsive forces between molecular entities or groups within the same molecular entity (i.e., both intermolecular and intramolecular) not due to bond formation or to electrostatic interactions of ions or ionic groups with one another or with neutral molecules. The origin of van der Waals forces is in electric polarization of uncharged atoms, groups, or molecules and includes dipole-dipole interactions, dipole-induced dipole interactions, and London forces (induced dipole-induced dipole interactions). 

Give an example for each type of intermolecular forces, (a) dipole-dipole interaction, (b) dipole-induced dipole interaction, (c) ion-dipole interaction, (d) dispersion forces, (e) van der Waals forces... 

There are several types of intermolecular forces ion-dipole, dipole-dipole, hydrogen bonding, dipole-induced dipole, and dispersion forces. As we discuss these intermolecular forces (also called van der Waals forces), look at Table 12.2, which compares them with the stronger intramolecular (bonding) forces. 

Three kinds of intermolecular forces can be traced to electrostatic attractions dipole forces, induced dipole forces, and hydrogen bonds. 

Other things being equal, which produces stronger intermolecular attractions, induced dipole forces or dipole forces ... 

Dipole forces, induced dipole forces, and hydrogen bonds are all intermolecular attractions—forces that act between molecules. Induced dipole forces are also known as dispersion forces, London forces, and London dispersion forces. Covalent bonds are the forces that hold atoms together within a molecule. Ionic bonds are the forces that hold ions together within a crystal. Covalent and ionic bonds are much stronger than any of the intermolecular 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... 

Van der Waals forces (Section 2 17) Intermolecular forces that do not involve ions (dipole-dipole dipole/mduced dipole and induced dipole/induced dipole forces)... 

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. 

A polar molecule can also induce a dipole on a neighbouring molecule that possesses no permanent dipole. The resultant intermolecular attraction between the permanent and the induced dipole is spoken of as the induction force. Its magnitude is small and independent of temperature. 

Induced-dipole/induced-dipole attractions are ver-y weak forces individually, but a typical organic substance can par ticipate in so many of them that they are collectively the most impor tant of all the contributor s to intermolecular- attraction in the liquid state. They are the only forces of attraction possible between nonpolar- molecules such as alkanes. 

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. 

In Chapter 6, the polarizability of molecules was considered as one factor related to both London and dipole-induced dipole intermolecular forces. The data shown in Table 9.6 confirm many of the observations that can be made about physical properties. For example, in the case of F2, Cl2, and Br2, the London forces that arise from the increase in polarizability result in a general increase in boiling point. 

These are the weakest of all intermolecular bonds. They result from the random movement of electrons within an atom or molecule. This movement can result in a separation of charge across the atom or molecule (an instantaneous dipole Fig. 11.7). This small separation of charge (indicated by <5+ and 8 ) will then influence neighboring atoms or molecules, and cause an induced dipole. These van der Waals bonds (sometimes known as London forces) occur between nonpolar molecules or atoms such as I2, 02, H2, N2, Xe, Ne, and between the aliphatic chains of lipids (see below). 

Ion-Induced Dipole and Dipole-Induced Dipole Intermolecular Forces... 

In this chapter, you have learned about intermolecular forces, the forces between atoms, molecules, and/or ions. The types of intermolecular forces include ion-dipole forces, hydrogen bonding, ion-induced and dipole-induced forces, and London (dispersion) forces. 

These types of attraction occur when the charge on an ion or a dipole distorts the electron cloud of a nonpolar molecule and induces a temporary dipole in the nonpolar molecule. Like ion-dipole intermolecular forces, these also require two different species. They are fairly weak interactions. 

This intermolecular attraction occurs in all substances, but is significant only when the other types of intermolecular forces are absent. It arises from a momentary distortion of the electron cloud, with the creation of a very weak dipole. The weak dipole induces a dipole in another nonpolar molecule. This is an extremely weak interaction, but it is strong enough to allow us to liquefy nonpolar gases such as hydrogen, H2, and nitrogen, N2. If there were no intermolecular forces attracting these molecules, it would be impossible to liquefy them. 

Ion-induced dipole intermolecular forces occur between an ion and a nonpolar molecule. 

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