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Exam 3 (70 pts) This Wednesday (2 May) Only a week to go !!!

Exam 3 (70 pts) This Wednesday (2 May) Only a week to go !!!. Exam 3 topics (70 pts) Using PV= nRT to determine MW, reaction ID Kinetic Theory of Gases and Ideal Gas Concepts Atomic Modeling (know relative dimensions of atom and its sub-nuclear parts)

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Exam 3 (70 pts) This Wednesday (2 May) Only a week to go !!!

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  1. Exam 3 (70 pts) This Wednesday (2 May) Only a week to go !!!

  2. Exam 3 topics (70 pts) • Using PV=nRT to determine MW, reaction ID • Kinetic Theory of Gases and Ideal Gas Concepts • Atomic Modeling (know relative dimensions of atom and its sub-nuclear parts) • Atomic models (Thomson, Rutherford, Bohr) • Electronic configuration assignments • Ionic compound formulas • Lewis modeling (octet/non-octet) • Bond orders and resonance (?) • True/False Ick

  3. Ionic compound prediction redux: crossing rule I haz my `ion’ you

  4. In-Class practice: Deducing formulas for ionic compounds Ca + Cl CaCl2 Al2O3 Al + O B + N BN K + S K2S Mg+ As Mg3As2

  5. What do we do when the compound can’t be ionic ??? O2, N2….? Use: Lewis’s valence bond (octet) model

  6. Lewis `octet’ model (see also pp. 378) The Entire Lewis model In a nutshell: • All bonds contain two electrons. • All elements except H and He1 seek an outer (valence) shell of 8 electrons. • If you can –minimize formal charge. • For elements from P onwards, you can break the octet rule and use rule 3. 1H and He are satisfied with 2 electrons= `duet’ rule

  7. IN-CLASS BOARD OCTET RULE PRACTICE WITH:: Diatomics O2N2CO

  8. What is the most likely Lewis structure for Cl2 ? • Double bonded so • Single bonded so: • Single bonded so: • Triple bonded so:

  9. IN-CLASS BOARD OCTET RULE PRACTICE (continued):: • Multi-atom, neutral compounds1 Tri, tetratomics CO2 H2O OF2 COCl2 1How do we know what bonds to what ? • Some rules of thumb: • Atoms closer to center of Periodic Table are in center of molecule • Molecules tend to be symmetric.

  10. IN-CLASS BOARD OCTET RULE PRACTICE WITH:: Diatomics O2N2CO tri, tetra-atomics CO2 H2O OF2 COCl2

  11. Which structure below satisfies the Lewis octet rule for SOBr2 ? • all single bond • S=O double • S=Br double • None of the above

  12. IN-CLASS BOARD OCTET RULE PRACTICE WITH:: Diatomics O2N2CO  tri,tetra-atomics CO2 H2O  OF2 COCl2  oxyanions NO3- CO3- SO42-

  13. Which is the best structure for SO32- that satisfies the Lewis octet rule • All single S-O • 1 S=O,2 S-O • 2 =O, 1 S-O • All S=O

  14. IN-CLASS BOARD OCTET RULE PRACTICE WITH:: Diatomics O2N2CO  tri,tetra-atomics CO2 H2O  OF2 COCl2  oxyanions NO3-  CO32- SO42- Are we safe with the octet rule ??? Chemistry sucks… The problem with octet rule: H2SO4 (and SO2 SO3 SO42- ….. and many other examples) stink up Lewis’s world

  15. BEYOND THE OCTET RULE: FORMAL CHARGE UGLY CHEMICAL FACT OF LIFE #1: For elements starting with Si in the 3rd row, the octet rule is often broken. EXAMPLE #1: BATTERY ACID (H2SO4) Lewis octet prediction for H2SO4 structure From Experiment (Kuczkowski et. al. 1983)

  16. We-work-it Examples where formal charge is minimized even if we break the octet rule. a) SO2 SO3 SO42- What is the octet rule prediction for SO2? 0   VS. 0 0 + and – formal charges Lewis rule 3 says not good No formal charges anywhere. Lewis rule 3 says good !

  17. Which is the best structure for PO42- that satisfies the minimize formal charge rule ?

  18. U-Do-it Examples where we minimize formal charge or simply break octet rule (continued) c) HClO4 ClO41- What will be the Cl-O bond order in ClO4-? (2+2+2+1)/4 =7/4= 1.75

  19. IN-CLASS BOARD OCTET RULE PRACTICE WITH:: Diatomics O2N2CO  tri,tetra-atomics CO2 H2O  OF2 COCl2  oxyanions NO3-  CO32- SO42- Non-Lewis formal charge rule H2SO4SO2  SO3 SO42-  Any other problems ? Yes ! Non-Lewis ”got no choice” and radicals PF5 SF6NO2

  20. Examples where we minimize formal charge or simply break octet rule because of the atom count on central atom. PF5 SF6

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