1. Chapter 9: Molecular orbitals: O 2 ; Cl 2 ; benzene 2. OWL 3. Preview of final exam: American Chemical Society First Semester General Chemistry

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Debra Kelly
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1 Makeup Exam 3 should be taken at Testing Services 211 Gruening Bldg (you need to have checked with JK to do this) If you simply must have your laptop turned on in class (for scientific purposes of course), sit at the back of the auditorium. If you do not wish to see laptop displays, sit at the front of the auditorium. Chem 105 Friday Chapter 9: Molecular orbitals: O 2 ; Cl 2 ; benzene 2. OWL 3. Preview of final exam: American Chemical Society First Semester General Chemistry 11/18/2011 1

2 O 2 contains 12 valence electrons (16 e- total). O O BUT O 2 is paramagnetic.. liquid O 2 (bp -182 C)? N S This fact (and the whole resonance situation) suggests that Lewis formulas don t always tell the whole story, and we need a more sophisticated theory for molecular structure which is Molecular orbital theory 11/18/2011 2

3 General scheme for diatomic molecules For given molecule or molecular ion, calculate total # electrons, then FILL UP from lowest. Pauli Principle and Hund s Rule apply. 11/18/2011 3

4 What is the bond order of the N 2 + ion? /18/2011 4

5 Answer: Bond order = 2.5 Bond order = 2.5 N 2 + contains 13 electrons 11/18/2011 5

6 What is the bond order of the N 2 - ion? /18/2011 6

7 Misconception: Adding electrons increases the bond order. Answer: Bond order = 2.5! N 2 - contains 15 electrons The net effect is no additional bonding. (the 14 th electron goes into 2p and the 15 th electron goes into * 2p Bond order = /18/2011 7

8 O 2 contains 16 electrons. O 2 is paramagnetic due to unpaired electrons. liquid O 2 (bp -182 C) Bond order = 2.0 N S Paramagnetism is NOT PREDICTED by Lewis formula 11/18/2011 8

9 Cl 2 Benzene Buckminsterfullerene Carbon nanotubes Molecules (or ions) with resonance portions contain several π-bonds that extend over several atoms. 11/18/2011 9

10 Benzene -MO 11/18/ Buckminsterfullerene (C 60 ) -MO

11 Final exam preview American Chemical Society First Semester General Chemistry Exam. Weighted 100 points (out of total of 650 for semester total) 120 min (standard final time block at UA) 70 multiple choice questions, including Ch /18/

12 Chem 105X covers Chapters 1-11 of Chemistry & Chemical Reactivity, 8 th Ed. (This is coverage is required by the UAF Chemistry faculty and the American Chemical Society, our accrediting body.) Four major themes: Stoichiometry, which is the application of conservation of atoms in chemical reactions and properties of gases. Electronic structure of atoms, which determines the placement of elements in the Periodic Table. Electronic structure of molecules, which determines their shape, polarity, and physical/chemical/biological properties Scientific math, including significant figures derived from measurements, and the use of measurement units. 11/18/

13 Important topics 1. Sig. figs (mult/div; add/sub); unit conversions; metric prefixes; d = m/v 2. Protons/neutrons/electrons; isotopes; mole->mass; periodic table sections. Ion formulas/names/charges; ionic compound formulas; binary compound names and formulas; determining empirical and molecular formulas. 3. Balancing chemical equations; limiting reactant; % yield; Solubility of ionic compounds; precipitation rxns; 4. Stoichiometry acid names and formulas; acid-base rxns; oxidation #s; identifying oxidation-reduction rxns; gasforming reactions (SO 2, CO 2, H 2 S, NH 3 ); molarity (M). chemical analysis. 5. Heating curves; using ΔH rxn ; Hess s Law; calorimetry; using ΔH f ; ΔH rxn =ΣΔH f (prod)-σδh f (react). 6. c=λn; E=hn; Rydberg given if necessary; excitation and emission; quantum #s and orbitals of H atom. 11/18/

14 7. Quantum #s, configurations of larger atoms (incl first row Transition Metals); confign of ions (e - w/ highest n lost first); trends in atom size, electronegativity, ionization potential. 8. Valence e - ; Lewis structures; Octet Rule; large atoms expanded octet; Be&B sub-octet; resonance; electron pair geometry (names); molecular geometry (names and angles); formal charges on atoms; estimating molecular polarity (Is it =0.0? Which is greater?). 9. Hybridization and geometry; diatomic molecular orbital theory, including bond order, para- and diamagnetism; π- and σ-bonds. 10. Structural isomers of alkanes, alkenes, alkynes. Recognize aromatic, alcohol, ether, ketone, aldehyde, carboxylic acid, ester functional groups; geometric isomers of alkenes. 11. Use of PV=nRT. Precepts of kinetic-molecular theory. Comparison of ideal vs. real gas, including two factors that appear in van der Waals equation. Temperature and molar mass dependence of molecular speeds. Know and use Kelvin (absolute) temperature scale. 11/18/

15 Sections we skipped that will NOT be covered on the final exam: Ch 5, Sect on First Law of Thermodynamics (P-V work and all that) Fuels interchapter Ch 6, f-orbitals Ch 7, Electron affinity Ch 10, any chemical reactions of organic compounds except hydrogenation (C=C + H 2 CH-CH using a metal catalyst) Ch 10, Most of common organic names (except acetic acid). Systematic names of alcohols, ketones, aldehydes, acids, esters, amides. Ch 10, Polymers Biochemistry interchapter 11/18/

16 Preparing for ACS Exam in General Chemistry This book was originally designed for the two-semester general chemistry exam. Therefore it contains Chem 106 material that you must work around. 1. Atomic structure all. Remember E = hn = hc/l No nuclear reactions 2. Molecular structure. May be something about ionic compounds and crystals. 3. Stoichiometry. Heavy emphasis. Study analysis section 4.4 in Kotz. % yield, limiting reactant 4. States of matter. PV=nRT No phase diagrams or multiple-phase problems. 5. Energetics = thermochemistry. No DG or entropy 6. Dynamics = kinetics (Chem 106 only) 7. Equilibrium = K eq and all that. (Chem 106 only) 8. Electrochemistry. Oxidation numbers and identifying redox reactions, oxidizing agent, reducing agent. No quantitative 9.Periodic Trends. Size/electronegativity/everyday chemicals. 11/18/

17 Information Provided 11/18/

18 Ch. 11 Next week Which equations do we need to remember? E h n c ln q mc D T D H D H PV u rxn rxn H BE nrt o f 2 u rms mc ( T ( prod ) H broken f 3 RT M T ) i BE o f made ( react ) (Qualitative only) 11/18/

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20 g Al 1 mol Al g Al x10 atoms 1 mol Al 3.3 x10 22 atoms 10. Balance equation : How many moles of 4 M 3 O M were oxidized? 2 2 M O mol M mol M 2O mol M mol M 2O3 g M g M Molar mass M 45.0 g/mol mol M mol M (at wt of Scandium (Sc)) 11/18/

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22 µ = 0.00 D µ > 0 D µ = 0.00 D µ = 0.00 D (C) N has 3 electron clouds (lone pair, = bond, - bond), which is trigonal planar electron pair geometry with a 120 bond angle. Also, N is sp 2 hybridized. So, you would say that the local molecular geometry at N is bent. 11/18/

23 The End 11/18/

CHEM 121 Lecture Planner

CHEM 121 Lecture Planner Lecture Lecture 1 Lecture 2 Lecture 3 Lecture 4 Lecture 5 Topics The Scientific Method Theories & Laws Quantitative Measurements vs Qualitative Measurements Accuracy & Precision