Intermolecular Forces - the forces of interaction between molecules.

Ion-Dipole Forces - solubility of ionic compounds in water

Van der Waals Forces - a general term for all the different forces which cause intermolecular attraction to occur.

Dipole-Dipole Forces - attractive force resulting from the alignment of polar molecules such that the positive end of one molecule is near the negative end of another.

London Forces - weak attractive forces between molecules resulting from small, instantaneous dipoles that occur because of the varying positions of the electrons during their motion about the nuclei. London Forces tend to increase with increasing molecular weight and with polarizability.

Polarizability - ease of distortion of the electron cloud about the molecule or atom.

Hydrogen Bonding - weak to moderate attractive force that exists between a hydrogen atom covalently bonded to a very electronegative atom, X, and a lone pair of electrons on another small, electronegative atom, Y. Represented as:

-X-H Y- Hydrogen bonding generally only occurs when X and Y are F,O, and N.

The Liquid State - Physical properties can be explained on the basis of the intermolecular forces.

Surface Tension - the energy required to increase the surface area of a liquid by a unit amount.

Surface area tends to be reduced as much as possible. This is why drops of water are spherical. This is because molecules at the surface experience a net attraction by the molecules in the interior of the liquid.

Capillary Rise - when a small diameter tube of glass is placed into water the water crawls up the sides of the glass tube due to the attractive force between the water molecules and the glass wall. As this occurs the surface area of the water increases, to decrease the surface area the water level rises. The level to which it rises it related to the attractive forces between the water molecules and the glass and the surface tension of water.

In the case of Mercury (Hg) note the level of mercury in the tube falls. This is due to the fact that the mercury atoms are more attracted to each other than to the glass surface. Note also the difference in the shapes of the meniscuses for the two liquids.

Viscosity - the resistance to flow. Typically measured by the time required for a specific mass and size steel ball to fall a given distance in the liquid.

Solids - characterized by relatively high density, low compressibility, and definite shape.

Molecular Solids - solid consisting of atoms or molecules held together by intermolecular forces.

Metallic Solid - solid consisting of positive cores of atoms held together by a surrounding "sea" of electrons.

Ionic Solid - solid consisting of anions and cations held together by electrostatic forces.

Covalent Network Solid - solid consisting of atoms held together in large networks or chains by covalent bonds.

Relationship Between Physical Properties and Structure