Chemistry 1B, Fall 2013 Lectures 24

Transcription

1 where we ve been and where the (almost) last 1B lectures take us Lecture 24 Intermolecular forces have studied intramolecular forces among atoms or ions within a molecule covalent forces ionic forces metallic bonding extended covalent bonding (graphite, diamond, graphene) coordinate covalent (transition metal complexes; Lewis acid-base) now what about intermolecular forces among differing molecules 1 2 examples of phenomena that depend on intermolecular forces physical states and intermolecular forces (Fig. 16.1; Silber table 12.1) physical states (phases) and phase changes ( solid liquid gas ) secondary and tertiary structure of biologically important molecules (how differing parts of a large molecule interact to form its full 3-D structure) Intermolecular forces (vs T) weak moderate strong 3 4 types of intramolecular (bonding) and intermolecular force energies of intramolecular (bonding) forces intramolecular ionic covalent metallic coordinate covalent (transition metal complexes; Lewis acid-base) intermolecular ion-dipole hydrogen bonding dipole-dipole ion-induced dipole dipole-induced dipole dispersion (London, van der Waals) see handout: Intermolecular Forces and slide #19 (Silberberg Table 12.2) 5 6 1

2 ion-dipole intermolecular forces: ion (polar) polar dipole-dipole intermolecular forces: polar polar Na + - O + + C O + Cl I + I Cl + I Cl 7 8 ordering by dipole-dipole forces (figure 16.2) ion-induced_dipole and dipole-induced_dipole (polar nonpolar) isolated e Lower T igher T 9 10 more dipole induced dipole dispersion forces (instantaneous dipoles): (non-polar non-polar) nonpolar dipole induced dipole

3 dispersion forces (instantaneous dipoles; figure 16.5) dispersion forces (animation) hydrogen bonds (very important!!) small electronegative atom with lone pair (N, O, F) 2 O B: A -bond small electronegative atoms: hydrogen bonded to electronegative atom N,O,F F..: O.. O=.. N or :N W8: 75. Zumdahl #16.24 greater bond polarity; greater -bond stability (exothermic) F - (g) + F(g) ö FF - Δ= (C 3 ) 2 C=O(g) +F(g) ö (C 3 ) 2 C=O º F Δ= O(g) + 2 O(g) ö 2 O º O (ice) Δ= - 21 weaker weakest where would ~N º ~O~ and ~N º ~N~ 15 fall in the above series? 16 hydrogen bonds in biological molecules (RNA and DNA) hydrogen bonds in biological molecules (protein secondary structure)

4 summary (Silberberg: table 12.2) FINAL EXAM WILL BE FROM EXAMPLES IN LECTURE Now some factoids and examples. Problems on final will be based on understanding of these specific examples!! strong moderate Take ome message on each slide!! weaker depends stay tuned molecular structure and intermolecular forces (problem 71 and 72) polarizability: strength of induced and spontaneous dipoles 71. What are the most important intermolecular forces between the following molecules and atoms: a. NaCl (aq) b. Fe 2+ and O 2 c. C 3 Cl and CCl4 d. examples from table in handout (slide #19) polarizability: how free the electrons in an atom or molecule are to slosh around induced and spontaneous dipoles are larger if atom or molecule is more polarizable 72. Zumdahl #16.15 Identify the most important types of interparticle forces present in the solids of each of the following substances examples: a. Ar; e. C 4 ; k. CCl 3 ; l. N 3 21 periodic trends in polarizability: increases down a group (outer electrons further away) decreases across a period (higher Z eff, more tightly held) anions are more polarizable than parent neutral atom (lower Z eff ) cations are less polarizable than parent atom (higher Z eff ) 22 boiling points, melting points, vapor pressure and intermolecular forces (nonpolar compounds, Table 16.2; table 16.8, Silberberg fig. 12.7) greater polarizability greater intermolecular forces higher melting (freezing) and boiling points, lower vapor pressure boiling points and intermolecular forces (nonpolar compounds; 16.19a) greater molecular surface greater dispersion forces higher boiling points melting point, strength of intermolecular forces ] ~ LE increased polarizability increased freezing point boiling point in Kº problem 73. #16.18 a,c a. highest boiling point Br, Kr, or Cl 2 Br > [Cl 2 >?Kr] c. lowest vapor pressure at 25ºC Cl 2, Br 2, or I 2 I 2 <Br 2 < Cl

5 nanofur from NANOSYS (Palo Alto) Subscriber Services Complete Forecast Posted on Sat, News Opinion Business Business Extra Financial Markets Technology Personal Technology Personal Finance Stock Options People & Events Drive Real Estate Sports Creating a sticky situation By Dean Takahashi Mercury News If humans ever gain the ability to crawl up walls like geckos, you can bet that it might have something to do with nanotechnology research. Creating an artificial version of the tiny fibers on geckos' toes is just one research project among many at Nanosys in Palo Alto. Even if the product, dubbed "nano fur,'' doesn't pan out in consumer products such van der Waals forces more gecko ( Getting a Grip, p 769) boiling points and intermolecular forces (Prob 16.19, Silb. fig. 12.8) molecules with equivalent molecular weight (ie size and polarizability and intermolecular dispersion forces) 27 polarity (dipole moment) and boiling point 28 surface tension (Zumdahl fig. 16.6, 16.7; Silb fig ) surface tension (Silberberg table 12.3; sample problem 16.29) intermolecular forces differ for molecules at surface and in bulk greater intermolecular forces greater surface tension IMF extra: molecules at surface have higher energy than those in bulk ; liquids for spherical droplets to minimize surface area

6 concave vs convex meniscus (Zumdahl fig 16.7; Silberberg fig ) why does ice float (see figure 16.12) 2 O is polar and can form hydrogen bonds (macho intermolecular forces) igh surface tension and capillarity ydrogen bonds form very open structure in solid 2 O (ice) giving ice a lower density than 2 O liquid. ICE FLOATS!! 2 O greater forces with glass than 2 O concave and high capillarity g greater forces with g than glass convex ice bomb!!!! solubility and intermolecular forces NaCl(s) Na + (aq) + Cl - (aq) C 2 5 O + 2 O C 2 5 O (aq) C O C O C 6 14 (aq) C CCl 4 solution solubility and intermolecular forces solubility and intermolecular forces (ionic solids + polar solvent) whether a substance dissolves in solvent (solubility), or two liquids mix (miscibility) is determined by two factors: NaCl(s) Na + (aq) + Cl - (aq) [ion-ion] [ion-dipole] things like to get mixed up, S[olutions] appen unless too endothermic (entropy, chem 1C) things like to give off heat (stability of products, interparticle forces in products vs those in reactants; chem 1B)

7 solubility and intermolecular forces (two polar liquids) solubility and intermolecular forces (nonpolar + polar) C 2 5 O + 2 O C 2 5 O (aq) ethyl alcohol.. C C O + 2 O C C O.. C O C 6 14 (aq) hexane C C C C C C only weak dispersion and dipole-induced dipole forces among hexane and water molecules immiscible nonploar molecules: hydrophobic solubility and intermolecular forces (nonpolar + nonpolar) C CCl 4 solution does dissolve solubility and intermolecular forces practical applications of immiscibility in general (likes dissolve in likes) polar molecules will form solutions with polar molecules nonpolar molecules will form solutions with nonpolar molecules polar and nonpolar substances will not form solutions lava lamps

8 hydrophilic vs hydrophobic hydrophilic: likes water; polar molecules or polar parts of molecules soap and detergents: hydrophilic + hydrophobic hydrophobic nonpolar hydrophilic polar hydrophobic: dislikes water; likes nonpolar environments; nonpolar molecules or parts of molecules soap detergent soap- takes the grime right down the drain micelles in biology (cell and other membranes) (phospholipids detergent-like molecules) micelles and membranes Graphene (2010 Nobel Prize) lecture 9 Graphene is a one-atom-thick planar sheet of sp 2 -bonded carbon atoms that are densely packed in a honeycomb crystal lattice. micelles bilayer membranes delocalized bonds interesting properties conjugated of graphene 47 p-system sp 2 carbons unhybridized p-orbitals 48 8

9 Chemistry 1B, Fall 2013 Week of December 2 nd -9 th Week of December 2-6- all regular sections and office hours Monday December 2 Sample Exam on ecommons Cumulative Review Outline on Chem1B WWW andouts Lecture: Review Kinetics and Spectroscopy Tuesday December 3 Extra Office ours: Switkes 2:15-3:15PM Wednesday December 4 Lecture: Intermolecular Forces W #9 (kinetics) WA due; solutions on ecommons Thursday December 5 Sample Exam Key on ecommons Friday December 6 Last lecture (get yourselves there!!) Extra Office ours: Switkes 9:00-10:00AM Saturday December 7 Class Review Session :30AM, Thimann 3 (Gene S.) Monday December 9 FINAL EXAM 8:00-11:00 AM M final exam: 8:00-11:00AM on Monday, 9 th December see you there!! 50 Finis!!! BUT one MORE TING 51 9