Chemistry 65.100 A, V
Midterm Test #2
November 6, 1998

Part A. Answer each question with a few sentences or equations where necessary. (5 Marks each)

1. What kind of hybrid orbitals does boron use in forming BF₃?
2.    What is meant by the term "standard state"?
3.    What are the oxidation numbers of each element in the following compounds?
        (a) PCl₅
      (b) H₃AsO₃
4. Draw a molecule of PCl₃ and clearly show the direction of the dipole in each bond, and the overall dipole moment of the molecule.
5. Reaction A is much faster than Reaction B, and has fewer steps. From this information alone, what can we say about the DH values of these two reactions?
6. How can arsenic form compounds such as AsCl₅, which clearly has more than 8 valence electrons around the As atom?

1.    Using VSEPR theory, predict the shapes of the following species. Wrong name of shape = zero marks.
        (a) GeCl₄ (b) ICl₃ (c) SeO₂

2. Balance the following REDOX reaction in basic solution:

S₂O₆^-2_(aq) + ClO₂^- _(aq) à SO₄^-2_(aq) + Cl_2(g)

3. Use a Born-Haber cycle to calculate the lattice energy (in kJ/mol) of BaH₂ given the following data:
Energy of vaporization of Ba_(s): 175.4 kJ mol^-1
First ionization energy of Ba: 502 kJ mol^-1
Second ionization energy of Ba: 963 kJ mol^-1
Bond dissociation energy of H₂: 436 kJ mol^-1
Electron affinity of H: -73 kJ mol^-1
Energy of formation of BaH_2(s) from the elements: -40.9 kJ mol^-1 

 4. A molecular orbital diagram for the C₂ molecule is shown below.
(a) What is the bond order of C₂?
(b)Would the bond length of C₂⁺ be greater or less than that of C₂? Explain why.
(c)Would the bond energy of C₂^- be greater or less than that of C₂? Explain why.
(d)Which, if any, of C₂, C₂⁺ and C₂^- are paramagnetic? Explain why.