1. Chapter 11 Intermolecular Forces, Liquids, and Solids Jeremy Wolf

2. 3 Common States of Matter

3. Intermolecular Forces Forces that hold together molecules and atoms (both electrically neutral species) are referred to collectively as van der Waals forces –Dipole-dipole attraction Hydrogen bonding with O-H, N-H, and H-F –London dispersion force

4. Dipole-Dipole Results from permanent dipoles OH, NH, and HF are particularly strong

5. London Dispersion Force Caused by chance instant where more electrons are located on one side of the atom Leads to an induced dipole in neighboring atom Instantaneous dipole

6. Liquids Viscosity is a fluid's resistance to flow –Strong attraction = high viscosity –Low temperature = high viscosity Surface tension is a cohesive intermolecular attraction that causes a liquid to minimize its surface area –intermolecular forces that bind similar molecules together are called cohesive forces –Intermolecular forces that bind a substance to a surface are called adhesive forces –Adhesive forces are responsible for liquids rising up very narrow tubes (and water rising up the stems of plants) through capillary action

7. Phase Changes Energy changes vs. state of matterHeating curve for water The energy associated with melting a solid is called the heat of fusion; the energy associated with vaporizing a liquid is called the heat of vaporization; and the energy associated with the sublimation of a solid is called the heat of sublimation. For a given substance, the heat of vaporization will always be greater than the heat of fusion. Imparting enough energy to molecules to allow them to move past one another takes less heat than separating the molecules completely

8. Vapor Pressure A substance with relatively weak intermolecular forces will have a greater tendency to escape into the vapor phase and will exhibit a higher vapor pressure then a substance with stronger intermolecular forces. A substance with a high vapor pressure is said to be volatile

9. Structures in Solids Amorphous solids do not have any order and are heterogeneous in their intermolecular forces Crystalline solids are highly ordered –highly ordered network of a repeating unit called a unit cell –A crystal lattice is a three-dimensional array of points called lattice points, each of which is identical –Primitive, Body-centered, Face-centered

11. Comparison of Packing Efficiency Packing SchemeCoordination Number Percent of Space Filled Hexagonal close packing1274 Cubic close packing1274 Body-centered cubic868 Primitive cubic652

12. Bonding in Solids Molecular solids compounds held together by dipole-dipole interactions and dispersion forces Covalent-network solids - giant molecules held together by covalent bonds Ionic solids consist of ions held together by electrostatic attractions Metallic solids consist of metal atoms held together by a "sea" of delocalized (same energy level) valence electrons