Chapter 9. Molecular Geometry and Bonding Theories

Transcription

1 Sample Exercise 9.1 (p. 347) Use the VSEPR model to predict the molecular geometries of a) O 3 b) SnCl 3 - Practice Exercise 1 (9.1) Consider the AB 3 molecules and ions: PCl 3, SO 3, AlCl 3, SO 3 2-, and CH 3 +. How many of these molecules and ions do you predict to have a trigonal-planar geometry? a) 1 b) 2 c) 3 d) 4 e) 5 Practice Exercise 9.1 Predict the electron-domain geometry and the molecular geometry for a) SeCl 2 b) CO

2 Sample Exercise 9.2 (p. 354) Use the VSEPR model to predict the molecular geometry of a) SF 4 b) IF 5 Practice Exercise 1 (9.2) A certain AB 4 molecule has a square-planar molecular geometry. Which of the following statements about the molecule is or are true? (i) The molecule has four electron domains about the central atom (ii) The B-A-B angles between neighboring B atoms is 90 o. (iii) The molecule has two nonbonding pairs of electrons on atom A. a) Only one of the statements is true. b) Statements (i) and (ii) are true. c) Statements (i) and (iii) are true. d) Statements (ii) and (iii) are true. e) All three statements are true. Practice Exercise 2 (9.2) Predict the electron-domain geometry and molecular geometry of a) BrF 5 + b) SF

3 Sample Exercise 9.3 (p. 355) Eyedrops for dry eyes usually contain a water-soluble polymer called polyvinylalcohol, which is based on the unstable organic molecule called vinyl alcohol. Predict the approximate values for the H-O-C and O-C-C bond angles in vinyl alcohol. Practice Exercise 1 (9.3) The atoms of the compound methylhydrazine, CH 6 N 2, which is used as a rocket propellant, are connected as follows (note that lone pairs are not shown): See p. 356 in your textbook. What do you predict for the ideal values of the C-N-N and H-N-H angles, respectively? a) o and o b) o and 120 o c) 120 o and o d) 120 o and 120 o e) None of the above Practice Exercise 2 (9.3) Predict the H C H and C C C bond angles in the molecule shown, called propyne

4 Sample Exercise 9.4 (p. 357) Predict whether the following molecules are polar or nonpolar: a) BrCl b) SO 2 c) SF 6 Practice Exercise 1 (9.4) Consider an AB 3 molecule in which A and B differ in electronegativity. You are told that the molecule has an overall dipole moment of zero. Which of the following could be the molecular geometry of the molecule? a) Trigonal pyramidal b) Trigonal planar c) T-shaped d) Tetrahedral e) More than one of the above Practice Exercise 2 (9.4) Determine whether the following molecules are polar or nonpolar: a) SF 4 b) SiCl 4-4 -

5 Sample Exercise 9.5 (p. 365) Describe the orbital hybridization around the central atom in NH 2 -. Practice Exercise 1 (9.5) For which of the following molecules or ions does the following description apply? The bonding can be explained using a set of sp 2 hybrid orbitals on the central atom, with one of the hybrid orbitals holding a nonbonding pair of electrons. 2- a) CO 2 b) H 2 S c) O 3 d) CO 3 e) more than one of the above Practice Exercise 2 (9.5) Predict the electron-domain geometry and the hybridization of the central atom in SO

6 Sample Exercise 9.6 (p. 368) Formaldehyde has the Lewis structure Describe how the bonds in formaldehyde are formed in terms of overlaps of hybridized and unhybridized orbitals. Practice Exercise 1 (9.6) We have just arrived at a bonding description for the formaldehyde molecule. Which of the following statements about the molecule is or are true? (i) Two of the electrons in the molecule are used to make the π bond in the molecule. (ii) Six of the electrons in the molecule are used to make the σ bonds in the molecule. (iii) The C-O bond length in formaldehyde should be shorter than that in methanol, H 3 COH. a) Only one of the statements is true. b) Statements (i) and (ii) are true. c) Statements (i) and (iii) are true. d) Statements (ii) and (iii) are true. e) All three statements are true. Practice Exercise 2 (9.6) Consider the acetonitrile molecule: a) Predict the bond angles around each carbon atom b) Describe the hybridization at each of the carbon atoms c) Determine the total number σ and π bonds in the molecule

7 Sample Exercise 9.7 (p. 371) Describe the localized π bonding in the nitrate ion, NO 3 -. Practice Exercise 1 (9.7) How many electrons are in the π system of the ozone molecule, O 3? a) 2 b) 4 c) 6 d) 14 e) 18 Practice Exercise 2 (9.7) Which of the following molecules or ions will exhibit delocalized bonding? SO 2, SO 3, SO 3 2-, H 2 CO, NH 4 +? Sample Integrative Exercise (p. 386) Elemental sulfur is a yellow solid that consists of S 8 molecules. The structure of the S 8 molecule is a puckered, eight-membered ring. Heating elemental sulfur to high temperatures produces gaseous S 2 molecules.: S 8(s) 4 S 2(g) a) With respect to electronic structure, which element in the second row of the periodic table is most similar to sulfur? b) Use the VSEPR model to predict the S-S-S bond angles in S 8 and the hybridization at S in S 8. d) Use bond enthalpies (Table 8.4) to estimate the enthalpy change for the reaction just described. Is the reaction exothermic or endothermic? - 7 -