As a liquid is heated, the kinetic energy of its particles increases. At the boiling point, the energy is sufficient to overcome the force of attraction between the liquid’s particles. The particles pull away from each other and enter the gas phase. Boiling point is therefore a good measure of the force of attraction between particles of a liquid. Using this information, along with Table 7 in your notes, put the four main bonding types in order from greatest to least force of attraction between particles.

The higher the boiling point, the more energy it takes to overcome the forces of attraction. Thus, the forces of attraction between particles are stronger.

There are 2 types of attraction in molecules: intramolecular bonds & intermolecular forces Intermolecular forces (IMF) have to do with the attraction between molecules, whereas intramolecular forces have to do with the attraction between atoms within a molecule. We have already looked at intramolecular bonds (ionic, polar and nonpolar covalent) We will focus on three types of IMF’s (dipole-dipole, hydrogen bonding, and London dispersion forces)

The strongest intermolecular forces exist between polar molecules. The negative region in a polar molecule attracts the positive region in an adjacent molecule. These forces are short range, acting only between nearby molecules.

The picture illustrates the dipole-dipole forces between molecules of IF. In each molecules, the highly electronegative chlorine atom has a partial negative charge, leaving each iodine atoms with a partial positive charge. Consequently, the negative and positive ends of neighboring molecules attract each other.

Some hydrogen-containing compounds have unusually high boiling points. In compounds containing H-F, H-O, or H-N bonds, the large electronegativity differences between the hydrogen and F, O, or N, make the bonds connecting them highly polar. This type of intermolecular force is called hydrogen bonding: When a H atom that is bonded to F, O, or N, and is attracted to an unshared pair of electrons in a nearby molecule Hydrogen bonds are usually represented by dotted lines.

Even noble-gas atoms and molecules that are nonpolar experience a weak intermolecular attraction. WHY? Electrons are in continuous motion and at any instant the electron distribution may be slightly uneven. The momentary, uneven charge creates a positive pole in on part of the atom or molecule and a negative pole in another. This temporary dipole can then induce a dipole in an adjacent atom or molecule. The two are held together for an instant by the weak attraction between the temporary dipoles: known as LONDON DISPERSION FORCES

London dispersion forces act between ALL atoms and molecules, but they are the ONLY intermolecular forces acting among noble-gas atoms and nonpolar molecules. The strength of London forces increases with increasing atomic or molar mass because the number of electrons are also increasing.