CHM1045
Spring 1999
Dr. Michael Blaber

Exam #3 100 points total

Mon July 19th 1999

  1. Using Lewis dot structures, indicate the movement of electrons during the formation of the ionic compound Beryllium Bromide from Beryllium (Be) and Bromine (Br) atoms (5 points)

 

 

 

 

 

 

 

2. Ordinary table salt (NaCl) is an ionic compound of sodium and chlorine. Sodium ion has a radius of 0.97Å, and the chlorine ion has a radius of 1.81Å. What is the magnitude of the attractive potential energy between the two ions in NaCl? (k = 8.99 x 109 J m/C2) (5 points)

 

 

 

 

 

 

 

3. For each of the noble gases below give an example of a cation that is isoelectronic with the noble gas (5 points)

He Ne Ar Kr Xe

4. Of the following ions, which is the smallest? Cl-, Br-, K+, Ca2+ (5 points)

 

 

5. What are the five steps to follow when drawing a Lewis Structure for an ABn type of molecule? Note: the correct sequence is essential! (5 points)

 

 

 

 

 

6. Draw the Lewis Structure for the carbonate ion, CO32- (Note: carbonate is an ABn type of molecule, with C as the central atom) (5 points)

 

 

 

 

 

 

 

7. For the following bonds, indicate whether you would expect the bonds to be ionic, polar covalent, or nonpolar covalent (5 points)

O-O

H-Br

H-F

H-P

Na-F

8. For each of the following possible Lewis Structure(s) of the PSiO- ion, indicate the formal charges on the atoms and based on the formal charges indicate the most probable structure (8 points)

 

 

 

 

 

 

9. The combustion of ethane (see structure below) with oxygen produces water and carbon dioxide. Write the balanced equation for the combustion of ethane (5 points). Based upon bond enthalpies (see last page), calculate the reaction enthalpy for the combustion of 1mol of ethane (5 points)

 

 

 

 

10. Give the names for the following molecular geometries (5 points)

 

 

11. The GeF3- ion is an ABn type molecule (Ge is central atom). Draw the Lewis Structure (2 points). Give the electron pair geometry (2 points) and the molecular geometry (2 points) for this ion.

 

 

 

 

 

 

 

 

12. The SeCl4 molecule is an ABn type molecule (Se is central atom). Draw the Lewis Structure (2 points). Give the electron pair geometry (2 points) and the molecular geometry (2 points)

 

 

 

 

 

 

 

 

13. The molecule F2SiO is an ABn type molecule (with Si as the central atom). Draw the Lewis Structure (2 points). What is the expected angle between F, Si and O atoms (2 points)? What is the expected angle between F, Si and F atoms (2 points)?

 

 

 

 

 

 

 

 

 

14. Give three examples of molecular geometries for ABn type molecules that would not have an overall dipole even if the individual bonds were covalant polar bonds. Give three examples of molecular geometries for ABn type molecules that would have an overall dipole if the individual bonds were covalent polar bonds (6 points)

 

 

 

 

 

 

 

15. Give the electron pair geometry, expected hybrid orbitals and molecular geometry for the atoms in the following structure (6 points)

16. For the following resonance structure of the NO3- ion, draw a valence orbital diagram for each atom (12 points)

 

 

 

Exam III Appendix

Constants

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

C-C 348