1. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 1 Intermolecular Forces Forces between (rather than within) molecules.  dipole-dipole attraction: molecules with dipoles orient themselves so that “+” and “  ” ends of the dipoles are close to each other. Ô hydrogen bonds: dipole-dipole attraction in which hydrogen is bound to a highly electronegative atom. (F, O, N)

2. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 2 London Dispersion Forces 4 relatively weak forces that exist among noble gas atoms and nonpolar molecules. (Ar, C 8 H 18 ) 4 caused by instantaneous dipole, in which electron distribution becomes asymmetrical. 4 the ease with which electron “cloud” of an atom can be distorted is called polarizability.

3. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 3 Some Properties of a Liquid Surface Tension: The resistance to an increase in its surface area (polar molecules). Capillary Action: Spontaneous rising of a liquid in a narrow tube. Viscosity: Resistance to flow (molecules with large intermolecular forces).

4. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 4 Types of Solids Crystalline Solids: highly regular arrangement of their components [table salt (NaCl), pyrite (FeS 2 )]. Amorphous solids: considerable disorder in their structures (glass).

5. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 5 Representation of Components in a Crystalline Solid Lattice: A 3-dimensional system of points designating the centers of components (atoms, ions, or molecules) that make up the substance.

6. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 6 Representation of Components in a Crystalline Solid Unit Cell: The smallest repeating unit of the lattice. 4 simple cubic 4 body-centered cubic 4 face-centered cubic

7. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 7 Bragg Equation Used for analysis of crystal structures. n = 2d sin  d = distance between atoms n = an integer = wavelength of the x-rays

8. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 8 Types of Crystalline Solids Ionic Solid: contains ions at the points of the lattice that describe the structure of the solid (NaCl). Molecular Solid: discrete covalently bonded molecules at each of its lattice points (sucrose, ice).

9. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 9 Packing in Metals Model: Packing uniform, hard spheres to best use available space. This is called closest packing. Each atom has 12 nearest neighbors. 4 hexagonal closest packed (“aba”) 4 cubic closest packed (“abc”)

10. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 10 Bonding Models for Metals Electron Sea Model: A regular array of metals in a “sea” of electrons. Band (Molecular Orbital) Model: Electrons assumed to travel around metal crystal in MOs formed from valence atomic orbitals of metal atoms.

11. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 11 Metal Alloys 1. Substitutional Alloy: some metal atoms replaced by others of similar size. brass = Cu/Zn Substances that have a mixture of elements and metallic properties.

12. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 12 Metal Alloys (continued) 2.Interstitial Alloy: Interstices (holes) in closest packed metal structure are occupied by small atoms. steel = iron + carbon 3.Both types: Alloy steels contain a mix of substitutional (carbon) and interstitial (Cr, Mo) alloys.

13. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 13 Network Solids Composed of strong directional covalent bonds that are best viewed as a “giant molecule”. 4 brittle 4 do not conduct heat or electricity 4 carbon, silicon-based graphite, diamond, ceramics, glass

14. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 14 Semiconductors 4 Conductivity is enhanced by doping with group 3a or group 5a elements. A substance in which some electrons can cross the band gap.

15. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 15 Vapor Pressure... is the pressure of the vapor present at equilibrium.... is determined principally by the size of the intermolecular forces in the liquid.... increases significantly with temperature. Volatile liquids have high vapor pressures.

16. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 16 Melting Point Molecules break loose from lattice points and solid changes to liquid. (Temperature is constant as melting occurs.) vapor pressure of solid = vapor pressure of liquid

17. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 17 Boiling Point Constant temperature when added energy is used to vaporize the liquid. vapor pressure of liquid = pressure of surrounding atmosphere

18. Copyright©2000 by Houghton Mifflin Company. All rights reserved. 18 Phase Diagram Represents phases as a function of temperature and pressure. critical temperature: temperature above which the vapor can not be liquefied. critical pressure: pressure required to liquefy AT the critical temperature. critical point: critical temperature and pressure (for water, T c = 374°C and 218 atm).