大学化学课件CHAPTER11【荐】.pdf

Chapter 11 : Intermolecular Forces Text sections 11.1 – 11.8 Key Concepts States of matter and intermolecular forces Vaporization, vapour pressure Sublimation and melting Phase diagrams Intermolecular Forces : Surface Tension Intramolecular forces are interactions of atoms within a molecule. Intermolecular forces are interactions between molecules. Among other things, intermolecular forces are responsible for condensation of gases, and freezing of liquids into solids. Exs of intermolecular forces in liquids: 1) Surface tension 2) Viscosity 3) Vapour pressure Intermolecular Forces : Surface Tension Molecules in the Molecules at the interior of a liquid surface of a liquid are surrounded have fewer by neighbouring neighbouring molecules. molecules. Because of the increased number of interactions, molecules in the bulk of solution are at a lower energy state than those on the surface. Intermolecular Forces : Surface Tension So why does a steel pin float on water ? Steel is much denser than water, it should sink to the bottom. as pin sinks, forces water from interior of liquid to surface. energy required to do this is larger than work done by gravity on the needle. Van der Waals (VdW) Forces Intermolecular forces, although they are weak compared to covalent and ionic bonds, play an important role in determining physical parameters such as boiling points. We will consider VdW forces arising