CHM 1045
Dr. Michael Blaber

Name_________________________

SS #__________________________

Exam #3 100 points total

  1. Using Lewis dot structures, indicate the movement of electrons during the formation of the ionic compound Calcium Oxide (CaO) from Calcium (Ca) and Oxygen (O) (5 points)

  2. If the atomic radius of the Calcium ion in question #1 is 0.99 x 10-10 m and the atomic radius of the Oxygen ion is 1.40 x 10-10 m what will be the magnitude of the attractive potential energy between the two charged ions in CaO ? (k = 8.99 x 109 J m /C2) (5 points)

    3. = 8.99 x 109 J m/C2 * (2*1.602 x 10-19 C)2/(0.99 x 10-10 m + 1.40 x 10-10 m)

    =3.86 x 10-18 J

     

     

  3. Provide an example of four ions in an isoelectronic series with 36 electrons (8 points)

    4. Se2-, Br-, Rb+, Sr2+

     

  4. Which of the following ions is the largest? Ca2+, K+, Cl-, S2- (5 points)

    5. S2-

  5. Draw the Lewis structure of the Sulfate (SO42-) ion (5 points)

  6. What is the formal charge on the Sulfur atom in the sulfate ion? What is the formal charge on an Oxygen atom in the sulfate ion? (5 points)

    7. S = +2

    O = -1

     

  7. Draw the Lewis structure for SeO3 (5 points)

    8.  

  8. Based on formal charge analysis, which of the following Lewis structures of phosphate ion (PO43-) is the most likely? (5 points)

    9. (the second one)

  9. Given the bond energies on the last page of the exam, estimate the enthalpy associated with the combustion of methane (CH4). (8 points)

    10. CH4 + 2O2 -> CO2 + 2H2O

    Bonds broken:

    4 x C-H = 4 x 413 = 1652

    2 x O=O = 2 x 495 = 990

    Bonds formed:

    2 x C=O = 2 x -799 = -1598

    4 x O-H = 4 x -463 = -1852

    total: 1652+990-1598-1852 = -808 kJ

  10. What is the oxidation number for the Carbon and Oxygen atoms in the carbonate ion (CO32-)? (4 points)

    11. Oxygen is more electronegative than C, so the oxidation number for O would be –2

    This would leave an oxidation number of +4 for the Carbon

     

  11. Name the following shapes for typical ABn type molecules: (8 points)

    12. Trigonal pyramidal Tetrahedral Trigonal bipyramid Octahedral

     

  12. Draw a Lewis structure for iodine pentafluoride (IF5). What is the valence electron pair geometry and molecular geometry of the molecule? (5 points)

    13. Valence = octahedral

    Molecular = square pyramidal

  13. Give the approximate values for the bond angles indicated in the following molecule: (6 points)

    14.  

    1. Slightly greater than 120°

    2. Slightly less than 109.5°

    3. 109.5°

  14. Give the valence electron geometry, expected hybrid orbitals, and molecular geometry for the indicated atoms in the following structure: (9 points)

    15.  

    1. Trigonal planar, sp2, trigonal planar

    2. Tetrahedral, sp3, bent

    3. Tetrahedral, sp3, tetrahedral

  15. For each the atoms indicated in the following structure, draw a valence electron orbital diagram (8 points)

    16.   

  16. For an ABn type of molecule, indicate which of the following molecular geometries would be result in a polar molecule and which would be non-polar: (9 points)

Trigonal planar Nonpolar

Tetrahedral Nonpolar

Trigonal pyramidal Polar

Bent Polar

T-shape Polar

Linear Nonpolar

Square planar Nonpolar

Octahedral Nonpolar

Trigonal bipyramidal Nonpolar

Exam III Appendix

Electron charge = 1.602 x 10-19 C

Bond energies (kJ/mol)

C-H 413

O=O 495

C=O 799

O-O 146

C-O 358

O-H 463