3.2answers - HOMEWORK #3,Part2 ANSWERS 1. Predict the...

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Unformatted text preview: HOMEWORK #3,Part2 ANSWERS 1. Predict the carbon-oxygen bond lengths in the formate ion given the below information and the structures shown for the ion. Carbon-to-Oxygen Bond Bond Length, pm triple 109 double 123 single 143 H C O O H C O O a. Both carbon-to-oxygen bond lengths are the same and intermediate between 143 pm and 123 pm. b. Both carbon-to-oxygen bond lengths are the same and intermediate between 123 pm and 109 pm. c. Both carbon-to-oxygen bond lengths are 123 pm. d. Both carbon-to-oxygen bond lengths are 143 pm. e. Both carbon-to-oxygen bond lengths are 109 pm Answer: a Resonance theory states that if two equivalent Lewis structures contribute to a resonance hybrid, the bonds are intermediate between those given in the separate Lewis structures. Since each structure consists of a C=O double (143 pm) and a C-O single (123 pm) bond, the actual bond length is intermediate between the two. 2. Which molecule is polar? a. SF 6 b. CF 4 c. NF 3 d. PF 5 e. BF 3 Answer: c All of the molecules except for NF 3 are symmetrical in such a way that their polar bonds cancel the dipole moment of each bond. NF 3 is a pyramidal molecule whose polar bonds are not cancelled by symmetry. 2 3. What is the best description of predicted shape of the OF 2 molecule? a. bent b. linear c. tetrahedral d. triangular e. planar Answer: a From the Lewis structure the steric number of OF 2 is 4 (two bonded atoms and two lone pairs). Thus the molecule is predicted to be bent, like water, OH 2 . 4.The central atom in which of the following molecules and molecular ions has a steric number of 4? a. SF 4 b. CCl 4 c. ICl 4- d. XeF 4 e. all of these Answer: b Only answer (b) has a steric number of 4. Answer (a) has a steric number of 5 (4 bonds, a lone pair on S); answer (c) has a steric number of 6 (4 bonds, two lone pairs on I) and answer (d) has a steric number of 6 (4 bonds, two lone pairs on Xe) 3 5 . According to the VSEPR theory, which of the following should possess a dipole moment? a. C 2 H 2 b. SO 2 c. CS 2 d. CO 2 e. None of the above Answer: b All of the molecules except for SO 2 are symmetrical in such a way that their polar bonds cancel the dipole moment of each bond. Linear molecules are symmetrical about their center if the central atom is surrounded by two identical atoms, since the dipoles cancel exactly. (a), (c) and (d) are linear molecules (steric number = 2). SO 2 , which has a lone pair on S, has a steric number of 3, is bent and possesses two polar bonds which do not cancel their dipoles. 6. According to the VSEPR theory the geometry of the bonding about the central sulfur atom in H 2 SO 4 (in which the H atoms are bonded to the O atoms) should be a. tetrahedral b. distorted pyramid c. seesaw d. square planar e. trigonal bipyramid Answer: a From the Lewis structure of H 2 SO 4 the S atom has a steric number of 4. Therefore, the atoms bonded to S are disposed in a tetrahedral shape about the S atom....
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3.2answers - HOMEWORK #3,Part2 ANSWERS 1. Predict the...

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