Extra Problems Solutions

Extra Problems Solutions - CHEM 212 (DE) Solutions to...

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CHEM 212 (DE) Solutions to Homework Problems page 1 of 38 1. Explain (in your own words) the difference between isomeric and resonance structures. Then a) Draw two isomeric structures for HONO and use formal charges to identify which isomer is more stable. b) Draw two nonequivalent resonance structures 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 CO 2 and HOCN molecules. Isomeric structures are structures for which there is a different arrangement of the atoms and (e.g. H-O-N=O versus H-N=O-O). Isomers have the same molecular formula but are different chemical compounds. Resonance structures are structures for which the arrangement of atoms is the same but for which there is a different arrangement of electrons around those atoms. Now for CO 2 . OC O O O -1 +1 -1 0 0 0 0 0 +1 These are different resonace structures for CO2. The second structure is the most important. O 0 0 0 COO 0 +2 -2 These are different isomeric structures for CO 2 . HONO 0000 HNOO 0- 1 + 1 0 HOON 00+ 1 - 1 The structures above are different isomers, each having the molecular formula HNO 2 . On the basis of formal charges, the first isomeric structure is the most stable. 0+ 1 1 The structures above are different resonance structures for HONO. On the basis of formal charges, the first resonance structure is the most important.
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CHEM 212 (DE) Solutions to Homework Problems page 2 of 38 And finally, for HOCN. Note: Other isomeric structures are possible (e.g. H-N=C=O which, on the basis of formal charges, is just as stable as H-O-C N). a) OC N isomer 1 isomer 2 00 0 fc = H 0 CN O H 0+ 1 - 1 0 b) N resonance structure 1 0 fc = H -1 0 resonance structure 2 N H +1 0 -2 0 N H +2 resonance structure 3 Based on formal charges, isomer 1 is more stable than isomer 2. Based on formal charges, resonance structure 1 is the major contributor to the structure of HOCN.
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CHEM 212 (DE) Solutions to Homework Problems page 3 of 38 2. Draw the most important Lewis structure for H 2 SO 4 plus three additional non-equivalent Lewis structures. Show all non-zero formal charges. Clearly identify the most important structure. S O OO H O H S O H O H S O H O H (I) (II) (III) (IV) S O H O H S O H O H (V) There are still other resonance structures. Structure (I) is the most important. -1 +1 -1 -1 +2 -1 -1 +1 +1 +1 +1 -1 -1
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CHEM 212 (DE) Solutions to Homework Problems page 4 of 38 Xe F F F F F F F F C 4 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) Br F 3 b) Br F 2 c) Xe F 4 d) B Cl 3 e) P O 4 3 f) S F 6 g) O 3 h) Xe O 3 i) S O 3 2 j) S O 2 k) F 2 O l) S F 4 m) N O 2 n) N O 3 o) Br F 5 p) I F 4 q) NN O r) I F 2 + a) b) c) d) e) T-shaped 90 o bond angles The point group is C 2v .
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This note was uploaded on 07/31/2011 for the course CHEM 212 taught by Professor Not sure during the Spring '09 term at Waterloo.

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Extra Problems Solutions - CHEM 212 (DE) Solutions to...

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