1_all_ - 1.1 Write Lewis Structures for each of the...

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1.1 Write Lewis Structures for each of the following: (a) HF (c) CH 3 F (e) H 2 SO 3 (g) H 3 PO 4 ( i) HCN (b) F 2 (d) HNO 2 (f) BH 4 - (h) H 2 CO 3 HF H C H H F ON O H O S O H O H FF H B H H H O P O H O H O H O C O H O H HC N 1.2 Write a Lewis structure for each of the following negative ions, and assign the formal negative charge to the correct atom. (a) NO 2 - (b) NH 2 - (c) CN - (d) HSO 4 - (e) HCO 3 - (f) HC 2 - Answer: (a) N O O (b) N H H (c) C N (d) S O O O O H (e)
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C O O O H (f) CC H 1.3 Assign the proper formal charge to the colored atom in each of the following structures: (a) HC H H C H H +1 (b) H O H H +1 (c) H C O O -1 (d) H C H H O (e) H C H N H H H H (f) H O H C H H H
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1.4 Write two resonance structures for the formula ion HCO 2 - . (b) Explain what these structures predict for the carbon-oxygen bond lengths of the formate ion and (c) for the electrical charge on the oxygen atoms. C H OO - C H - The structure predicts that the carbon-oxygen bond lengths will be between the carbon-oxygen single bond and carbon-oxygen double bond. And each oxygen atom should bear -1/2 negative charge. 1.5 (a) Consider a carbon atom in its ground state. Would such an atom offer a satisfactory model for the carbon of methane? If not, why not? (b) What about a carbon atom in the exited state: C 1s 2s 2px 2py 2pz Excited state of a carbon atom Would such a atom offer a satisfactory model for the carbon of methane? If not, why not? Answer: (a) The ground state of a carbon atom is: C 1s 2s 2px 2py 2pz It has only two unpaired electrons. So it only can form two covalent bonds with hydrogens. But in methane, there are four carbon-hydrogen bonds. C H H H H If it is combined with hydrogen atoms, the bond angle is 90 0 . Because the angle between 2P x and 2P y is 90 0 . So a carbon atom in its ground state can not offer a satisfactory model for the carbon of methane. (b) A carbon atom in the exited state can offer a satisfactory model for the carbon of methane. It has four unpaired electrons. So it can form four covalent bonds with hydrogens. 1.6 which of the following alkenes can exit as cis-trans isomers? Write their structures.
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a c d b Cl ANSWER only c and d exit as cis-trans isomers to c to d CC CH 3 H H 3 C H CH 3 H H 3 C H Cl H H H 3 CH 2 C Cl H H 3 CH 2 C H 1.7 Part of reasoning that led van't Hoff and Le Bel to propose a tetrahedral shape for molecules of methane was based on the number of isomers possible for substituted methanes. For example, only one compound with the formula CH 2 Cl 2 has ever been observed (i.e., there is no isomeric form). Consider both a square planar structure and a tetrahedral structure for CH 2 Cl 2 and explain how this observation supports a tetrahedral structure. If CH2Cl2' structure is square planar shape, it must has two isomers as follow: Cl H Cl H Cl H H Cl If CH2CL2' structure is tetrahedral structure, as we know it just has one structure. Only one compound with the formula CH 2 Cl 2 has been observed, so that we propose CH 2 Cl 2 'structure is a tetrahedal shape.
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This note was uploaded on 02/23/2010 for the course CHEM 101 taught by Professor Smith during the Spring '10 term at Duke.

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1_all_ - 1.1 Write Lewis Structures for each of the...

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