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Workpatch 6.1 Redraw each structure to get the electron groups as far apart as possible. What angles did you use? Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For all these problems, describe the geometry of the electron groups and name the molecular shape resulting from that geometry. Also, draw the molecule, and label the size of all bond angles in your drawing. 6.1 CO2. Answer: First draw a dot diagram, then examine it via VSEPR: Note: Don’t worry about the arrangement of the electron pairs about the peripheral (outer) atoms of a molecule. Only the electrons on the inner atoms affect the shape. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For all these problems, describe the geometry of the electron groups and name the molecular shape resulting from that geometry. Also, draw the molecule, and label the size of all bond angles in your drawing. 6.2 NH4+ (cation). Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For all these problems, describe the geometry of the electron groups and name the molecular shape resulting from that geometry. Also, draw the molecule, and label the size of all bond angles in your drawing. 6.3 C2Cl2, which is connected Cl—C—C—Cl. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For all these problems, describe the geometry of the electron groups and name the molecular shape resulting from that geometry. Also, draw the molecule, and label the size of all bond angles in your drawing. 6.4 COCl2, in which all atoms are connected to C, and there is a carbon–oxygen double bond. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 6.2 How would you describe the shape of the water and ozone molecules? Follow the convention! Ignore the lone pairs on each central atom. Cover them up and use a word or phrase that best describes the shape created by the atoms. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 6.3 The drawings preceding WorkPatch 6.2 give the ideal values for the bond angles in the molecules. Recalling that there is roughly a 2° compression from the ideal VSEPR angle for every lone pair on the central atom, give a more accurate bond angle for each molecule. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 6.4 We left three possible situations out of Table 6.2: 1. Four electron groups (SN = 4): one bonding group and three lone pairs. 2. Three electron groups (SN = 3): one bonding group and two lone pairs. 3. Two electron groups (SN = 2): one bonding group and one lone pair. These are considered trivial cases. Why? What shape(s) do these bonding situations give rise to? Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For each molecule or polyatomic ion in the following five problems, (a) draw the electron-group geometry, (b) name the shape of the molecule, and (c) estimate the size of all the bond angles in the molecule or ion. (Some of the molecules and ions have lone pairs on the central atom.) 6.5 PBr3. Answer: First draw a dot diagram (which must show 26 electrons): Next, count electron groups about the central atom. There are four (three single bonds and one lone pair), indicating a tetrahedral geometry of these groups about the P atom. However, because you must ignore the lone pair on P, the molecule is pyramidal in shape, with a predicted Br—P—B angle of less than 109.5°. (You might predict 107°, but P is not a period 2 element. The actual bond angle is 102 °.) Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For each molecule or polyatomic ion in the following five problems, (a) draw the electron-group geometry, (b) name the shape of the molecule, and (c) estimate the size of all the bond angles in the molecule or ion. (Some of the molecules and ions have lone pairs on the central atom.) 6.6 SO42– (anion). Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For each molecule or polyatomic ion in the following five problems, (a) draw the electron-group geometry, (b) name the shape of the molecule, and (c) estimate the size of all the bond angles in the molecule or ion. (Some of the molecules and ions have lone pairs on the central atom.) 6.7 HCN, in which hydrogen and nitrogen are attached to carbon. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For each molecule or polyatomic ion in the following five problems, (a) draw the electron-group geometry, (b) name the shape of the molecule, and (c) estimate the size of all the bond angles in the molecule or ion. (Some of the molecules and ions have lone pairs on the central atom.) 6.8 Sulfur dioxide, SO2, a pollutant that comes from burning coal contaminated with sulfur. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems For each molecule or polyatomic ion in the following five problems, (a) draw the electron-group geometry, (b) name the shape of the molecule, and (c) estimate the size of all the bond angles in the molecule or ion. (Some of the molecules and ions have lone pairs on the central atom.) 6.9 HNO3, in which hydrogen is attached to one of the oxygens and all oxygens are attached to nitrogen. To simplify, ignore the hydrogen when you name the molecule’s shape. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 6.5 When does a bond have a dipole moment of zero? Here is a hint for the Workpatch. The dipole moment will be zero only when the two atoms have no partial charges. When does this happen? What does a dipole moment of zero mean for the bond? Check your answer against ours at the end of the chapter. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 6.6 Which molecule is more polar? [Be careful!] Which molecule is more polar? Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 6.7 Why is the upward tug in COCl2 slightly stronger than either of the downward tugs? Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 6.10 Is phosphorus trichloride, PCl3, a polar molecule? If it is, draw the dipole moment vector for the entire molecule and show where the + and – regions of the molecule are. Answer: Yes, it is a polar molecule. PCl3 should have 26 electrons. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 6.11 Is chloroform, CHCl3, a polar molecule? If it is, draw the dipole moment vector for the entire molecule and show where the + and – regions of the molecule are. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 6.12 Show how the molecules of Problems 6.10 and 6.11 would arrange themselves if they were placed between two plates, one carrying a positive electrical charge and the other carrying a negative electrical charge. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 7.3 Draw a picture showing how NH3 molecules attract one another. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 7.7 (a) (b) (c) (d) Draw a dot diagram for NH3 and one for PH3. Is either molecule polar? (The electronegativities of N, P, and H are 3.0, 2.1, and 2.1, respectively.) In which substance are the London forces stronger? Explain. Basing your answer solely on the London forces in the two substances, which substance would you expect to have the higher boiling point? Explain. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Workpatch 7.3 The boiling point of one of these compounds is 35 ºC, and the boiling point of the other is 78 ºC: Which boils at which temperature? Why? If hydrogen bonds are involved in either case, make a drawing using dotted lines to show the hydrogen-bonding. Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 7.10 For the hydrogen halides, the order of boiling points is HF > HI > HBr > HCl. (a) Why does HF have the highest boiling point? (b) Why is the boiling point of HI greater than those of HBr and HCl? Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc. Practice Problems 7.12 How is a piece of iron similar to a piece of sodium chloride in terms of the forces that must be overcome to melt it? Introductory Chemistry, 4th Edition Steve Russo © 2011 Pearson Education, Inc.