CHM1045
Fall 2000
Dr. Michael Blaber

Name_______________________________SS#_________________________

Exam #4 100 points total

Tuesday December 12 2000

1. Use Lewis Symbols to show the reaction of Potassium and Sulfur atoms to produce the ionic compound Potassium Sulfide. Use arrows to indicate the appropriate movement of the valence electron(s) (5 points)

2. Draw Lewis Structures for the following molecules (6 points)

a) Ammonium Ion, NH4+

b) Carbon monoxide, CO

 

 

 

3. Draw the Lewis Structure for Selenium Trioxide, SeO3 (9 points)

NOTE: -4 points for no resonance structures

4. For the following pairs of Lewis Structures indicate the value for the formal charge on each atom, and indicate which structure of the pair is most likely correct (11 points)

a)

b)

NOTE: 0.5 POINTS EACH FOR CORRECT FORMAL CHARGE, 2 POINTS FOR CORRECT IDENTIFICATION OF STRUCTURE

5. Draw the Lewis Structure for the following compounds (10 points)

a) IF4-

b) SI5-

NOTE: -2 points per structure if bracket or charge sign is omitted

6. Using the following bond dissociation energies calculate DH for the combustion of 2.0 moles of ethane. Be sure to write the balanced equation, and show all your work. (12 points)

D(C-H) = 414 kJ/mol

D(C-C) = 347 kJ/mol

D(O=O) = 498 kJ/mol

D(C=O) = 799 kJ/mol

D(O-H) = 464 kJ/mol

2C2H6 + 7O2 ® 4CO2 + 6H2O (2 points)

Bonds Broken: (4 points)

12 mol (C-H) = (12 mol * 414kJ/mol) = 4,968 kJ

2 mol (C-C) = (2 mol * 347 kJ/mol) = 694 kJ

7 mol (O=O) = (7 mol * 498 kJ/mol) = 3,486 kJ

Bonds Formed: (4 points)

8 mol (C=O) = (8 mol * 799 kJ/mol) = 6,392 kJ

12 mol (O-H) = (12 mol * 464 kJ/mol) = 5,568 kJ

DH = (4,968+694+3,486) - (6,392+5,568) = -2,812 kJ (2 points)

7. Draw the Lewis Structure for the molecule SI4. What is the valence electron geometry of the central S atom? What is the molecular geometry of the SI4 molecule? (9 points)

(3 points)

Valence electron pair geometry: TRIGONAL BIPYRAMID (3 points)

Molecular geometry: (SEE-SAW) (3 points)

8. Which of the following molecular geometries would result in an overall molecular dipole for ABn type molecules (where A and B are different types of atoms with different electronegativities) (8 points)

a) Linear NO

b) T-shaped YES

c) Trigonal Planar NO

d) Bent YES

9. Name the type of hybrid valence orbitals and draw an orbital diagram for the hydbrid orbitals for all the atoms in the following Lewis Structure of the NO3- ion. (12 points)

a) O

sp3 (2 points)

 (2 points)

b) O

sp2 (2 points)

(2 points)

c) N

sp2 (2 points)

(2 points)

10. Draw the Lewis Structure of water. What is the valence electron geometry for the central Oxygen atom? What is the molecular geometry? What approximate angle(s) do you expect for the molecular geometry? (10 points)

(2points)

Oxygen valence electron geometry: TETRAHEDRAL (2 points)

Molecular Geometry: BENT (2 points)

H-O-H bond angle is approximately 109.5° (or slightly less due to repulsion by lone pair electrons) (4 points)

11. Using the electronegativity values provided on the table at the end of the exam, predict whether the following bonds will be ionic, polar covalent or non-polar covalent (8 points)

a) C-H

Polar covalent

b) C-S

Non-polar covalent

c) S-Na

Ionic

d) Si-O

Polar covalent

 

12. EXTRA-EXTRA CREDIT (5 POINTS)

WHAT DID DR. BLABER EAT FOR THANKSGIVING?

BOSTON MARKET CHICKEN (5 points)

 

13. EXTRA CREDIT (10 POINTS)

Using the following information draw a Born-Haber Cycle enthalpy diagram and determine the DH for the lattice energy of NaI(s):

Na+(g) + I-(g) ® NaI(s)

Na(s) + 1/2I2(s) ® NaI(s) DH = -288 kJ/mol

I2(s) ® I2(g) DH = +62 kJ/mol

Na(g) ® Na+(g) + e- DH = +496 kJ/mol

I(g) + e- ® I-(g) DH = -295 kJ/mol

Na(s) ® Na(g) DH = +107 kJ/mol

1/2I2(s) ® 1/2I2(g) DH = +31 kJ/mol

1/2I2(g) ® I(g) DH = +23 kJ/mol