2. Next to Last Lecture Last lecture is next Monday, Dec. 2. Review sessions 7 – 10 pm, 4xx Buehler Nov. 25, 26 and Dec. 2, 3, 4, 5, 6. Bring questions. Final exam on Monday, Dec. 9, 8 am. Today we discuss Chapter 11 with some review of hybridization and bond overlaps.

3. Phase Changes Matter exists primarily in three phases: solid liquid gas Both elements and compounds are found in these three phases, and are denoted by subscripts, e.g. N 2 (g), H 2 O (l), and Au (s).

4. Phase Changes The three phases interconvert with one another.

5. Phase Changes Interconversions of gases and liquids are called:

6. Phase Changes Interconversions of liquids and solids are called:

7. Phase Changes Interconversions of gases and solids are called:

8. Phase Changes AB – sublimation/depositionAD – melting/freezing AC – vaporization/condensation

9. Phase Changes Changing from a less dense phase to a more dense phase (e.g. condensation) is exothermic. Changing from a more dense phase to a less dense (e.g. vaporization) one is endothermic. For any two phases, the energy changes in both directions are equal in magnitude, but opposite in sign.  H vap = -  H con Recall that enthalpy is a state function.

10. Phase Changes H 2 O enthalpy of fusion (melting)

11. Phase Changes Liquids and their vapors are in equilibrium. Pressure of a vapors (gas phase) = vapor pressure of liquid Pressure and temperature are directly proportional. Recall PV = nRT

12. Phase Changes SCF = supercritical fluid

13. Phase Changes AB – sublimation/depositionAD – melting/freezing AC – vaporization/condensation

14. Phase Changes The temperature at which a liquid boils is called its boiling point (bp). Boiling point is a function atmospheric pressure, or the pressure above the solution. Normal boiling point is the boiling temperature of a liquid at 1 atmosphere (atm) pressure.

15. Phase Changes Critical temperature, T c, is the highest temperature at which liquid and vapor exist in equilibrium. Critical pressure, P c, is the vapor pressure at the critical temperature. Critical point is reached at T c and P c. Triple point is the temperature and pressure at which all three phases coexist.

16. Phase Changes H 2 O phase diagram C = T c, P c A = triple point

17. Phase Changes Phase diagram for HgI 2 (mercuric iodide) HgI 2 (  ) and HgI 2 (  ) are both solids but different phases.

18. The phase changes from solid to liquid to gas are governed by intermolecular forces. Intramolecular forces are the chemical bonding forces discussed previously. These intermolecular forces have both attractive and repulsive components. Collectively they are called van der Waals forces after the Dutch Nobel laureate (physics) who described them. Intermolecular Forces

19. Johannes Diderik van der Waals Van der Waals forces describe the behavior of a non-ideal gas, which includes both attractive and repulsive components. [P + a(n/V) 2 ](V-bn) = nRT

20. Intermolecular Forces All molecules exert weak attractions on one another due to the mutual attraction of nuclei and electrons. These attractive forces are only significant at very short distances. At such small distances the intermolecular repulsion of the electrons on different atoms is also significant.

21. Intermolecular Forces The electrons orbiting all atoms and molecules can be perturbed by an electric field, with greater or lesser ease. This property is called polarizability. The electron cloud around an atom or molecule can give an instantaneous dipole any time that the electrons are not distributed perfectly symmetrically. Such a dipole can induce dipoles in other species nearby.

22. Intermolecular Forces

23. The attractive forces between an instantaneous dipole and an induced dipole are called London dispersion forces after the physicist Fritz London. These forces are stronger for more polarizable species.

24. Intermolecular Forces Some molecules have a permanent dipole because of differences in electronegativities among the atoms. Such molecules experience dipole-dipole forces. All molecules experience dispersion forces and induced dipoles, and polar molecules also experience dipole-dipole forces.

25. Intermolecular Forces Dipole-dipole interactions.

26. Intermolecular Forces The intermolecular forces that we have seen London dispersion forces induced dipole interactions dipole-dipole interactions have a strong effect on the boiling points of liquids, along with the molecular weight of a compound, and hydrogen bonding.

27. Intermolecular Forces (a) CS 2 (b) CH 3 OH (c) CH 3 CH 2 OH (d) H 2 O (e) C 6 H 5 NH 2

28. Intermolecular Forces Hydrogen bonding is an additional type of bonding interaction that requires a hydrogen atom on one molecule and a source of electron density on another molecule, usually a lone pair. Hydrogen bonding can be intramolecular as well as intermolecular.

29. Intermolecular Forces

32. Boiling points of covalent hydrides

33. Intermolecular Forces Boiling points of covalent hydrides

34. Intermolecular Forces The second-row hydrides NH 3, H 2 O, and HF exhibit much higher boiling points that would be expected based on their molecular weights. Strong hydrogen bonding between the molecules is responsible for the large liquid phase range of these compounds. CH 4 has a low boiling point because it has no lone pairs to form strong hydrogen bonds.

35. Intermolecular Forces Hydrogen bonding is crucial for the double-helical structure of DNA. An understanding of hydrogen bonding between base pairs made the structural solution possible for James Watson and Francis Crick.

36. Intermolecular Forces DNA base pairs hydrogen bond between G-C and A-T

37. Structure and Bonding  bonds are in general stronger than  bonds and can be formed from either s or p orbitals:  bonds have no nodal planes along the line containing the two nuclei.

38. Structure and Bonding The  * antibonding orbital has one nodal plane between the two nuclei

39. Structure and Bonding  bonds have one nodal plane that contains both nuclei. The  * antibonding orbital also has one nodal plane between the nuclei.

40. Hybridization Review Recall: sp 3 hybridization4  bonds sp 2 hybridization3  bonds, 1  bond sp hybridization2  bonds, 2  bonds

41. Hybridization Review

49. Final Exam covers Chapters 1 –11 inclusively.