CHE 11, Fall 1998
Test 3
December 2, 1998

Multiple choice (2 points each)
1. Which of the following statements about hydrogen is false?

(a) H has a lower ionization energy than He.
(b) H^- is smaller than H.
(c) H bonds with the halogens to form polar covalent compounds.
(d) H does not have a second ionization energy.
(e) All of these statements are true.

2. Which of the following atoms or ions has 3 unpaired electrons?

3. List the following atoms in order of increasing ionization energy: C, F, Li, Na, O

(a) Li < Na < C < O < F
(b) Na < Li < C < O < F
(c) F < O < C < Li < Na
(d) Na < Li < F < O < C
(e) Na < Li < C < F < O

4. Select the best Lewis structure for acetone, CH₃COCH₃.

5. Which of the following atoms would be expected to have the largest electron affinity, releasing the greatest amount of energy when an electron is added?

Short Answer
6. What is the octet rule? Are there any exceptions to this rule? Explain, giving at least two examples. (8 points)

7. For each of the following molecules or ions: write a Lewis dot structure, predict the molecular geometry (including bond angles), describe the hybridization of the central atom, and show the direction of the dipole moment of the molecule (if it is polar). (7 points per molecule) (a) SO₃^2-
(b) IF₄^-
(c) XeF₆
(d) BF₃

8. (9 points)
(a) Draw a Lewis dot structure for the carbonate ion, CO₃^2-.

(b) Draw the other resonance structures for this ion, indicating formal charges on the atoms in one of the resonance structures.

(c) Draw the resonance hybrid for this ion. Explain briefly what the resonance hybrid means about the bonding in this ion.

9. Write the electron configurations for the following atoms or ions. (6 points)
(a) Cu
(b) P³⁺

10. Place the following ions in order of decreasing size. Explain your answer briefly. (5 points)

Ba²⁺, Cs⁺, I^-, La³⁺, Te^2-

Problems
11. Draw an energy level diagram for the molecular orbitals in O₂ and N₂. Explain why the removal of one electron in O₂ strengthens the bond, while the removal of one electron from N₂ weakens the bond. (8 points)

12. Given the following bond energies, estimate DH for the reaction shown. (6 points)

13. Draw an energy level diagram showing how electrons fill the atomic orbitals in silicon, Si. (5 points)

Essay. Write your answer in complete sentences, using proper grammar.
14. What are molecular orbitals? How do they compare with atomic orbitals? Your answer should discuss s and p orbitals as well as bonding and antibonding orbitals. (15 points)