CHEM 212 (DE) EXTRA PRACTICE PROBLEMS page 1 of 61. Explain (in your own words) the difference between isomeric and resonance structures. Then a) Draw two isomericstructures for HONO and use formal charges to identify which isomer is more stable. b) Draw two nonequivalent resonancestructures for the most stable isomer from part a). Use formal charges to decide which of your resonance structures is most important. Repeat parts a) and b) for the CO2and HOCN molecules. 2. Draw the most important Lewis structure for H2SO4plus three additional non-equivalent Lewis structures. Show all non-zero formal charges. Clearly identify the most important structure. 3. Draw the most important Lewis structure for each of the molecules or ions. (The underlined atom is the central atom. All of the other atoms are bonded directly to the underlined atom.) Then use VSEPR theory to predict the ideal bond angles. Finally, name the molecular geometry. a) BrF3b) BrF2−c) XeF4d) BCl3e) PO43−f) SF6g) O3h) XeO3i) SO32−j) SO2k) F2Ol) SF4m) NO2−n) NO3−o) BrF5p) IF4−q) NNO r) IF2+4. For the molecules or ions in question #3, identify the principal axis. Use a sketch to illustrate where the principal axis is. 5. For each of the molecules or ions in question #3, state whether the molecule possesses (i) a σhmirror plane, (ii) one or more σvmirror planes, and (iii) a centre of inversion, i. 6. Determine the molecular point group for each molecule or ion in question #3. 7. For each of the following molecules, determine the molecular point group. Briefly justify your answer. (The underlined atom is the central atom.) a) cis-N2F2b) trans-ClCH=CHCl c) C2H4d) HCN e) BrF5f) NOCl g) H2O2(in its “skew” form – see below) h) thiophene, C4H4S (see below) i) 1,3,5-tribromobenzene (see below) j) ferrocene, Fe(C5H5)2(in its staggered form – see below) k) B2H6(see below) l) XeF4m) HOCl n) cis-ClCH=CHCl o) SO3CCCCSHHHH(planar)BrBrHBrHHFeOOHHBHHBHHHH
CHEM 212 (DE) EXTRA PRACTICE PROBLEMS page 2 of 68. Determine the point group of spiropentane, C5H8. Use the figures below. 9. The BF3molecule belongs to the D3hpoint group. Use the character table for the D3hpoint group to classify the symmetries of the B(2s) and B(2pz) orbitals. Assume that the zaxis is perpendicular to the molecular plane and that the xaxis passes through one of the B-F bonds. (Note: You can assign the symmetry type by considering only the C3, C2, hσ, and vσsymmetry elements.) Use the character tables given on the next page. 10. In CHEM 120, you learned that the πbond in C2H4arises from the sideways overlap of the 2porbitals on the two carbon atoms. Later in this course, we will introduce an alternative description: the sideways interaction of two 2porbitals gives rise to a bonding orbital for the two πelectrons, labeled as π(2p) and we refer to that orbital as a bonding molecular orbital, as shown in the figures below. Use the character tables given on the previous page.
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