Arkansas State University 
Department of Chemistry
and Physics
CHEM4204
Exam 2

1. Predict the structure for PF3ClI and give the point group for this molecule.   (5 points)

2. Show how an S2 is the same as an inversion center   (5 points)

3. List all possible symmetry elements for the following: (10 points)

 a)   HCN
 b)   AsF3Cl2
 c)   your left shoe
 d)   ethane (eclipsed configuration)

4. Give the point group and tell which would be optically active and which have dipole moments.             (20 points)

 a)   CClFHI

 b)   H2S

 c)   SO42-

 d)   MoOCl4-  (square pyramidal)

 e)   cyclohexane (boat configuration)

5. The square pyramidal and trigonal bipyramidal structures are both five coordinate.  Which orbitals are used for the hybridization for each of these geometries?  Be specific.  Why is tbp preferred over sq. py. geometry for most 5 coordinate species?  (10 points)

6. Draw the Born-Haber cycle for KCl and label all parts.  Show how you would calculate the lattice energy for this cycle.  (10 points)

7. Calculate the lattice energy for CaO using the CsCl structure. Calculate the lattice energy for CaO using the NaCl structure.  Which would be more favorable? Explain your answer. (12 points) Madelung  Constants:  Rock Salt, 1.74756; CsCl, 1.76267. Ca-O  distance, 239 pm.

8. List the type of chemical forces and give the relationship between energy and distance.  Define polarizability. (10 points)

9. Determine the lattice types from the information given below for Na2O and CaO.  Ionic radii:  Na+ = 95 pm, Ca2+ = 99 pm,  O2-  = 140 pm   (8 points)

10. Calculate the Heat of Formation for CsBr from the Born-Haber cycle: DHI.E. = 375.7, DHE.A. = 324.6, DHdis = 190.2, DHvap = 278  kJ/mol.  Cs-Br distance, 364 pm.  CsCl structure. (10 points)