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04CHM114_0310

04CHM114_0310 - CHEM 114 $2004 Wed Mar 10 Lecture No 20 I...

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Unformatted text preview: CHEM 114 $2004 Wed. Mar 10 Lecture No 20 I and (advance)21 CHAPTER 9. Molecular shapes from simple e-pair repulsion theory. Back to electron pairs for simple interpretation of molecular geometry. VSEPR theory (valence shell electron pair repulsion) The shapes of molecules play an important role in their behavior especially 1n biology where‘ ‘lock and key” relations that are critical 1n “molecular recognition: depend 011 compatible shapes While most bio- molecules are huge and are not under consideration 1n this section, it is helpful to realize how simply the shapes of small molecules can be deduced from a very simple idea. The key idea is that electron pairs, whether bonding or non—bonding, want to stay away from one another as far as possible. ' We need: 1. Words for shapes of molecules 2. Words for different geometrical distributions of things like electron pairs (“electron domains”) 3. The ability to distinguish between the shapes describing the distribution of e-pairs and the shapes of the molecules (if all e-pairs were bonding, there would be no distinction, but mostly there are non-bondin g pairs playing an important role) For 1, see Fig. 9.2 “linear” “bent” “trigonal planar” “trigonal pyramid” “T—shaped” “tetrahedral” “trigonal bypyramid” “octahedra ” For 2', see Fig. 9.5 and Table 9.1 Electron pair repulsions imitated by common balloons. Balloons adopt the configurations they do because this way they minimize their repulsions (due to compression when they are forced into contact). This is a mechanical repulsion, but its effect is exactly the same as the electrostatic repulsion that electron pairs exert on each other. For 3. See Table 9.2. Consider the series CH4, NH3, H20 H Ill-J's,»- Pa. (rs. am: 1.- 'l‘Irt‘f‘d—Lc-isn-L ’. Hzagfiv "F “‘+r:hfih°h —. Fl LI-dn. phi? 1; bus-J- tn‘ (“ h H) 5‘ Ska-p... .5; hot off. hr" harm. «l.- d~$+r~|5u+jtan :t 3H.“ 11-“. bh‘ MI‘ {Ln-fl. :3 fi‘JQh-I-L Penn-34.“ , Non bonding pairs actually act as if they are bigger than bonding pairs. See Fig. 9.7. This makes non—bonding pairs congregate on the axis of the molecule (see SF4 below) Then consider PF5, PF6' ‘ ‘E” F: J6 T..- C 3‘ pain) —) 'h‘gow-l- lb; Pvt-amid . I “I file (t LII-lull +\ c M. “ 0 ‘ “3114*. s: nu +9 'S'h“. . PF" L 4,- Page: -—3 .oul-uLc—dcfi—t Shop. 9. Msme- use :5 «I: And SE; " ovu- Mt 1-0;. p :1}: F IV; F 3 C Sau- . And 15(ng (TBP), and XeF4 (oct) +0.“- P“) {4" If: 1-“'5°""“ What would you expect for effects of electrons in multiple bonds? E.g in COClz? Extra re ulsion from electrons in multi le bonds. (c p p o a. LI L I. ~ “ a. . Q30 “*9" --;.¢-:_" Mat-*1 (C: a, ‘ In CL POLARITY AND SHAPE. 1...;3. ,4 pt...“- Shape of molecules and distribution of bonding and non bonding electrons determines whether or not the molecule has an electric moment, and in particéular if it is dipolar. Large dipole moments make for good solvents of salts. Electronegativity plays an important role. Water is supreme, as a solvent, but others are also good. (see Fig.__,9. 12 also Fig. 9.13 lit-Wu... M‘s, h:- Calm 0 ,0: fisgoh " ‘ 0 ’ 5"” 1' In Jaw-m. ¢quhcfil CNN MW CM”? A; w‘J—n’fw "lw‘l‘i—KQL 10-: Human. read-«raw, L‘s-flung... July—hau- muf- lu, thaG-Lfiwn-rd.’ ".43- Ogl‘hlb “Cd'l-H g ’\ ’Lthm . Consie er water? acetonitrile, acetone, dimethyl sulfone, sulfolane "‘1" “‘13:... — M: :c - o’ I pic 6 9‘ law-sq, Japan N-le-a-J' ch l a. GHBUI-mfi‘c. ® 1 ‘ ‘ caulk 1M9]. CHAPTER 10. GASES AND GAS LAWS Simple laws and understandable theories (the best case for distinguishig between the concepts ”law” and ”theory”) (Qu. Which two of the following are best classified as the results of theory as opposed to laws of nature? The concepts of pressure (force per unit area) and of gas pressure. What does one atmosphere pressure mean? Why IS pressure LOWER when the atmosphere contains a lot of moisture? Devices for measuring pressure. Barometer see Fig. 10.2 Simp e way of measuring the mass of the earths’ atmosphere in kg. 4an mzx 0.76m x density of mercury (in kg/m3) r = radius of the earth Manometer see Fig. 10.3 ...
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