1. Ch 10: Intermolecular Forces and Types of Solids AP Chemistry Sequoyah High School

2. 2 10.1: Intermolecular Forces (IMF)  IMF < intramolecular forces (covalent, metallic, ionic bonds)  IMF strength: solids > liquids > gases  Boiling points and melting points are good indicators of relative IMF strength.

3. 3 10.1: Types of IMF 1.Electrostatic forces: act over larger distances in accordance with Coulomb’s law http://dwb4.unl.edu/ChemAnime/attractive_forces.htm a.Ion-ion forces: strongest; found in ionic crystals (i.e. lattice energy) http://chemmovies.unl.edu/ChemAnime/LICLD/LICLD.html

4. 4 b.Ion-dipole: between an ion and a dipole (a neutral, polar molecule/has separated partial charges)  Increase with increasing polarity of molecule and increasing ion charge.          Cl -          S 2- < Ex: Compare IMF in Cl - (aq) and S 2- (aq). http://wps.prenhall.com/wps/media/objects/439/449969/Media_Portfolio/Chapter_14/Dissolution_NaCl_Water.MO

5. 5 c.Dipole-dipole: weakest electrostatic force; exist between neutral polar molecules  Increase with increasing polarity (dipole moment) of molecule Ex: What IMF exist in NaCl (aq)? http://antoine.frostburg.edu/chem/senese/101/liquids/faq/h-bonding-vs-london-forces.shtml http://usm.maine.edu/~newton/Chy251_253/Lectures/CarbonylReduction/AldehydesKetones.html

6. 6 d.Hydrogen bonds (or H-bonds):  H is unique among the elements because it has a single e - that is also a valence e -. –When this e - is “hogged” by a highly EN atom (a very polar covalent bond), the H nucleus is partially exposed and becomes attracted to an e - -rich atom nearby. http://www.visionlearning.com/library/module_viewer.php?mid=57http://www.visionlearning.com/library/module_viewer.php?mid=57 ( ice and water simulation) http://www.youtube.com/watch?v=LGwyBeuVjhUhttp://www.youtube.com/watch?v=LGwyBeuVjhU ( H bond movie) http://www.youtube.com/watch?v=lkl5cbfqFRM&feature=relatedhttp://www.youtube.com/watch?v=lkl5cbfqFRM&feature=related ( H bonding in water)

7. 7  H-bonds form with H-XX', where X and X' have high EN and X' possesses a lone pair of e-  X = F, O, N (since most EN elements) on two molecules: F-H O-H N-H :F:O:N:F:O:N

8. 8  * There is no strict cutoff for the ability to form H-bonds (S forms a biologically important hydrogen bond in proteins).  * Hold DNA strands together in double-helix Nucleotide pairs form H- bonds DNA double helix

9. 9  H-bonds explain why ice is less dense than water. http://www.youtube.com/watch?v=PcoiLAsUvqc&feature=related http://www.youtube.com/watch?v=gmjLXrMaFTg&feature=related http://en.wikipedia.org/wiki/Water_%28molecule%29#Density_of_water_and_ice

10. 10 Ex: Boiling points of nonmetal hydrides Boiling Points (ºC) Conclusions:  Polar molecules have higher BP than nonpolar molecules ∴ Polar molecules have stronger IMF  BP increases with increasing MW ∴ Heavier molecules have stronger IMF  NH 3, H 2 O, and HF have unusually high BP. ∴ H-bonds are stronger than dipole-dipole IMF

11. 11 2.Inductive forces:  Arise from distortion of the e - cloud induced by the electrical field produced by another particle or molecule nearby.  London dispersion: between polar or nonpolar molecules or atoms –* Proposed by Fritz London in 1930 –Must exist because nonpolar molecules form liquids Fritz London (1900-1954)

12. 12 How they form: 1.Motion of e- creates an instantaneous dipole moment, making it “temporarily polar”. 2.Instantaneous dipole moment induces a dipole in an adjacent atom * Persist for about 10 -14 or 10 -15 second http://dwb4.unl.edu/ChemAnime/LONDOND/LONDOND.html Ex: two He atoms

13. 13 * Geckos!  Geckos’ feet make use of London dispersion forces to climb almost anything.  A gecko can hang on a glass surface using only one toe.  Researchers at Stanford University recently developed a gecko-like robot which uses synthetic setae to climb walls http://en.wikipedia.org/wiki/Van_der_Waals%27_force

14. 14 London dispersion forces increase with:  Increasing MW, # of e -, and # of atoms (increasing # of e - orbitals to be distorted) Boiling points: Effect of MW:Effect of # atoms: pentane36ºCNe–246°C hexane69ºCCH 4 –162°C heptane98ºC ??? effect: H 2 O 100°C D 2 O 101.4°C  “Longer” shapes (more likely to interact with other molecules) C 5 H 12 isomers: 2,2-dimethylpropane10°C pentane36°C

15. Summary of IMF Van der Waals forces

16. 16 Ex: Identify all IMF present in a pure sample of each substance, then explain the boiling points. BP(⁰C ) IMFExplanation HF20 HCl-85 HBr-67 HI-35 Lowest MW/weakest London, but most polar/strongest dipole-dipole and has H-bonds Low MW/weak London, moderate polarity/dipole-dipole and no H-bonds Medium MW/medium London, moderate polarity/dipole-dipole and no H-bonds Highest MW/strongest London, but least polar bond/weakest dipole-dipole and no H-bonds London, dipole- dipole, H-bonds London, dipole- dipole

17. 17 10.2: Properties resulting from IMF 1.Viscosity: resistance of a liquid to flow 2.Surface tension: energy required to increase the surface area of a liquid

18. 18 3. Cohesion: attraction of molecules for other molecules of the same compound 4. Adhesion: attraction of molecules for a surface

19. 19 5.Meniscus: curved upper surface of a liquid in a container; a relative measure of adhesive and cohesive forces Ex: HgH2OH2O (cohesion rules)(adhesion rules)

20. 20 10.8: Phase Changes Processes:  Endothermic: melting, vaporization, sublimation  Exothermic: condensation, freezing, deposition I 2 (s) and (g)Microchip

21. 21 Water: Enthalpy diagram or heating curve

22. 22 10.8: Vapor pressure A liquid will boil when the vapor pressure equals the atmospheric pressure, at any T above the triple point. http://glencoe.com/sites/common_assets/advanced_placement/chemistry_chang9e/animations/chang_2e/vapor_pressure.s wf http://dwb4.unl.edu/ChemAnime/VPTEMPD/VPTEMPD.html http://dwb4.unl.edu/ChemAnime/VP3LIQD/VP3LIQD.html Pressure cooker ≈ 2 atm Normal BP = 1 atm 10,000’ elev ≈ 0.7 atm 29,029’ elev (Mt. Everest) ≈ 0.3 atm

23. 23 10.9: Phase diagrams: CO 2  Lines: 2 phases exist in equilibrium  Triple point: all 3 phases exist together in equilibrium (X on graph)  Critical point, or critical temperature & pressure: highest T and P at which a liquid can exist (Z on graph)  For most substances, inc P will cause a gas to condense (or deposit), a liquid to freeze, and a solid to become more dense (to a limit.) Temp (ºC)

24. 24 Phase diagrams: H 2 O For H 2 O, inc P will cause ice to melt.

25. 25 *

26. 26 *

27. 27 10.3-7: Structures of solids  Amorphous: without orderly structure Ex: rubber, glass  Crystalline: repeating structure; have many different stacking patterns based on chemical formula, atomic or ionic sizes, and bonding

28. Types of crystalline solids (Table 11.6) TypeParticlesForces Notable properties Examples AtomicAtoms London dispersion  Poor conductors  Very low MP Ar (s), Kr (s)

29. Molecular Molecules (polar or non-polar) London dispersion, dipole- dipole, H- bonds  Poor conductors  Low to moderate MP CO 2 (s), C 12 H 22 O 11, H 2 O (s) Sucrose Carbon dioxide (dry ice) Ice

30. Ionic Anions and cations Electrostatic attractions  Hard & brittle  High MP  Poor conductors  Some solubility in H 2 O NaCl, Ca(NO 3 ) 2

31. Covalent (a.k.a. covalent network) Atoms bonded in a covalent network Covalent bonds  Very hard  Very high MP  Generally insoluble  Variable conductivity C (diamond & graphite) SiO 2 (quartz) Ge, Si, SiC, BN DiamondGraphiteSiO 2

32. Metallic Metal cations in a diffuse, delocalized e - cloud Metallic bonds  Excellent conductors  Malleable  Ductile  High but wide range of MP Cu, Al, Fe