Chemistry Exam 3 (100 points) December 5, b. solid HF

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1 hemistry Name Exam 3 (100 points) December 5, 2017 On my honor, I have neither given nor received unauthorized aid on this exam. Signed Date 1. (2 points) In which of the following will delocalized molecular orbitals be unlikely to be used to describe bonding? FNO 2 6 H 6 O 2-3 O 2 O 3 2. (3 points) The values listed below are the atomic radii (in picometers) for the following atoms: S, Na, P, Mg, Al, O, K. Match each radius with the corresponding element (2 points) Which element in question 2 above has the highest electron affinity? 4. (2 points). A "conduction band" extends over the entire lattice structure of a solid and is made up of a set of highly delocalized, partially filled. 5. (8 points) What is the strongest type of intermolecular force in each of the following? a. liquid XeF 2 b. solid HF c. liquid BrF 3 d. Agl dissolved in liquid Pl 3 6. (2 points) Tungsten (VI) fluoride, WF 6, is a gas at room temperature. At lower temperatures, it forms colorless crystals that melt at 2.3 to give a liquid that does not conduct electricity. The most likely crystal type (i.e., ionic, metallic, etc.) for solid WF 6 is 7. (6 points) Among aqueous solutions of HlO 4, NH 3, Al 2 O 3, HF, 2 H 5, Rb, P 2 O 5, and ao, which is(are) basic amphoteric acidic 8. (5 points) alculate the amount of heat that must be absorbed by 25.0 g of ice at 15.0 to convert it to liquid water at 60.0 given that the specific heat (ice) = 2.10 J/g, specific heat (water) = J/g, specific heat (steam) = 1.84 J/g., H vap = 40.7 kj/mol, and H fus = 6.02 kj/mol.. Show all work and all UNITS clearly.

2 2 9. The following compounds are used in the questions below. ethylene glycol S S carbon disulfide H 3 ethanol H 3 O acetic acid carbon tetrabromide, Br 4 dichloromethane l 2 H 3 O H 3 dimethyl ether H glycerol a. (3 points) Predict the order of viscosity of the pure substances: ethylene glycol, ethanol, and glycerol. least viscous < < most viscous b. (3 points) Which of the pure compounds in the table above has(have) ONLY dispersion forces? c. (3 points) Which of the molecules in the table above can form hydrogen bonds with water? d. (3 points) Predict the order of boiling point of the pure substances: water, dimethyl ether (H 3 OH 3 ), carbon dioxide (O 2 ), and KBr. lowest < < < highest 10. The following questions refer to the phase diagram of elemental iodine (I 2 ) as shown below (not drawn to scale). a. (3 points) What phase will exist after the following sequential transformations? the substance is cooled from 125 to 100 at a P (atm) D pressure of 1 atmosphere F the pressure is then lowered to 0.12 atmosphere 1.00 E the pressure is further decreased to 0.01 atm 0.12 B b. (1 point) Which letter on the diagram indicates the critical point of I 2? 0.02 A T ( o )

3 3 11. The molecular orbital diagram for the diatomic molecule BN is shown below. a. (2 points) omplete the labels (σ 2s, σ * 2s, etc.) of the energy levels on the diagram. B BN N b. (2 points) Fill in the diagram with the correct number of valence electrons for the individual atoms and for the BN molecule. c. (3 points) What is the bond order in each of the following species? BN 2p 2p BN 2s BN 2- σ 2s 2s d. (2 points) Which of the above has the shortest B-N bond distance? 12. (12 points) Apply VSEPR concepts to the following two compounds. a. sketch the Lewis dot structures, including resonance forms, taking care to minimize formal charges. b. draw a clear 3-dimensional structure, c. give a description (word) of the molecular shape (e.g., linear, square planar, etc.), d. indicate whether the molecule is polar or non-polar (write the word). If polar, indicate polarity with an arrow on your sketch. e. give the hybridization at each central atom FNO 2 HIO 3 (I as in iodine) 13. (6 points) The element silicon (Si) crystallizes in a "diamond cubic" unit cell in which there are eight Si atoms per unit cell. What is the edge length (l) of the unit cell in pm (picometers) if the density of Si is g/cm 3. Show all work and all UNITS clearly.

4 4 14. onsider the simple organic compound 2 H 3 NO, whose basic framework is indicated by dotted lines in the figure below. The numbers on the structure are merely labels to distinguish the carbon atoms in the questions below. O H H 1 2 N H a. (1 point) The total number of valence electrons in this molecule is. b. (2 points) In the space above, complete the Lewis electron dot formula for 2 H 3 NO. c. (3 points) What is the hybridization at each of the following atoms? O 2 N d. (1 point) The O 1 2 bond angle is about degrees. e. (1 point) The 2 N H bond angle is about degrees. f. (7 points) Describe the bonding in 2 H 3 NO using Valence Bond concepts (i.e., hybrid atomic orbitals, etc.). Draw and clearly label one or more pictures to show the types of orbitals that you are using to form the various σ and/or π bonds. Also clearly show the 3-D structure of the molecule, including the relative orientation of the geometric arrangements around O, 1, 2, and N. [Note: You need not write out a list because you should clearly label the sketches.] 15. (12 points) Apply VSEPR concepts to the following ions. In each case, draw a clear 3-D structure and give a description of the shape (i.e., tetrahedral, trigonal planar, etc.). Also, state the hybridization of the central atom in each case. (Do NOT draw orbital pictures!) - - BrF 4 Br 3 Brl + 2

5 hemistry Name Exam 3 (100 points) December 5, 2017 On my honor, I have neither given nor received unauthorized aid on this exam. Signed Date 1. (2 points) In which of the following will delocalized molecular orbitals be unlikely to be used to describe bonding? FNO 2 6 H 6 O 3 2- O 2 O 3 2. (3 points) The values listed below are the atomic radii (in picometers) for the following atoms: S, Na, P, Mg, Al, O, K. Match each radius with the corresponding element (2 points) Which element in question 2 above has the highest electron affinity? 4. (2 points). A "conduction band" extends over the entire lattice structure of a solid and is made up of a set of highly delocalized, partially filled. 5. (8 points) What is the strongest type of intermolecular force in each of the following? a. liquid XeF 2 b. solid HF c. liquid BrF 3 d. Agl dissolved in liquid Pl 3 6. (2 points) Tungsten (VI) fluoride, WF 6, is a gas at room temperature. At lower temperatures, it forms colorless crystals that melt at 2.3 to give a liquid that does not conduct electricity. The most likely crystal type (i.e., ionic, metallic, etc.) for solid WF 6 is 7. (6 points) Among aqueous solutions of HlO 4, NH 3, Al 2 O 3, HF, 2 H 5, Rb, P 2 O 5, and ao, which is(are) basic amphoteric acidic 8. (5 points) alculate the amount of heat that must be absorbed by 25.0 g of ice at 15.0 to convert it to liquid water at 60.0 given that the specific heat (ice) = 2.10 J/g, specific heat (water) = J/g, specific heat (steam) = 1.84 J/g., H vap = 40.7 kj/mol, and H fus = 6.02 kj/mol.. Show all work and all UNITS clearly.

6 2 9. The following compounds are used in the questions below. S S carbon disulfide H 3 ethanol H 3 O ethylene glycol acetic acid carbon tetrabromide, Br 4 dichloromethane l 2 H 3 O H 3 dimethyl ether H glycerol a. (3 points) Predict the order of viscosity of the pure substances: ethylene glycol, ethanol, and glycerol. least viscous < < most viscous b. (3 points) Which of the pure compounds in the table above has(have) ONLY dispersion forces? c. (3 points) Which of the molecules in the table above can form hydrogen bonds with water? d. (3 points) Predict the order of boiling point of the pure substances: water, dimethyl ether (H 3 OH 3 ), carbon dioxide (O 2 ), and KBr. lowest < < < highest 10. The following questions refer to the phase diagram of elemental iodine (I 2 ) as shown below (not drawn to scale). a. (3 points) What phase will exist after the following sequential transformations? the substance is cooled from 125 to 100 at a P (atm) D pressure of 1 atmosphere F the pressure is then lowered to 0.12 atmosphere 1.00 E the pressure is further decreased to 0.01 atm 0.12 B b. (1 point) Which letter on the diagram indicates the critical point of I 2? 0.02 A T ( o )

7 3 11. The molecular orbital diagram for the diatomic molecule BN is shown below. a. (2 points) omplete the labels ( 2s, * 2s, etc.) of the energy levels on the diagram. B BN N b. (2 points) Fill in the diagram with the correct number of valence electrons for the individual atoms and for the BN molecule. c. (3 points) What is the bond order in each of the following species? BN 2p 2p BN BN 2-2s 2s 2s d. (2 points) Which of the above has the shortest B-N bond distance? 12. (12 points) Apply VSEPR concepts to the following two compounds. a. sketch the Lewis dot structures, including resonance fomrs, taking care to minimize formal charges. b. draw a clear 3-dimensional structure, c. give a description (word) of the molecular shape (e.g., linear, square planar, etc.), d. indicate whether the molecule is polar or non-polar (write the word). If polar, indicate polarity with an arrow on your sketch. e. give the hybridization at each central atom FNO 2 HIO 3 (I as in iodine) 13. (6 points) The element silicon (Si) crystallizes in a "diamond cubic" unit cell in which there are eight Si atoms per unit cell. What is the edge length (l) of the unit cell in pm (picometers) if the density of Si is g/cm 3. Show all work and all UNITS clearly.

8 4 14. onsider the simple organic compound 2 H 3 NO, whose basic framework is indicated by dotted lines in the figure below. The numbers on the structure are merely labels to distinguish the carbon atoms in the questions below. H O H 1 2 N H a. (1 point) The total number of valence electrons in this molecule is. b. (2 points) In the space above, complete the Lewis electron dot formula for 2 H 3 NO. c. (3 points) What is the hybridization at each of the following atoms? O 2 N d. (1 point) The O 1 2 bond angle is about degrees. e. (1 point) The 2 N H bond angle is about degrees. f. (7 points) Describe the bonding in 2 H 3 NO using Valence Bond concepts (i.e., hybrid atomic orbitals, etc.). Draw and clearly label one or more pictures to show the types of orbitals that you are using to form the various and/or bonds. Also clearly show the 3-D structure of the molecule, including the relative orientation of the geometric arrangements around O, 1, 2, and N. [Note: You need not write out a list because you should clearly label the sketches.] 15. (12 points) Apply VSEPR concepts to the following anions. In each case, draw a clear 3-D structure and give a description of the shape (i.e., tetrahedral, trigonal planar, etc.). Also, state the hybridization of the central atom in each case. (Do NOT draw orbital pictures!) - - BrF 4 Br 3 Brl + 2

Bonding and IMF practice test MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question.

Exam Name Bonding and IMF practice test MULTIPLE CHOICE. Choose the one alternative that best completes the statement or answers the question. 1) There are paired and unpaired electrons in the Lewis symbol