1. Ozone (O3) is found in the upper atmosphere where it absorbs UV radiation and acts as a protective
'sunscreen.' a. Add non-bonding and bonding electron pairs to the partial Lewis structure shown below and
assign any necessary formal charges to the atoms in this structure. Write another equivalent resonance
structure for ozone, using the arrow-pushing technique and resonance formalism we learned in class. 6 pts
2
O
O
O
c. Experiments suggest that O3 has a measurable dipole
moment and all of its electrons are paired. Draw the
relevant bond and molecular dipole moments on the
structures you drew above. 3 pts
d. Is the experimental structure consistent with what
you would expect from VSEPR theory? 3 pts
YES / NO
e. Assign the orbital hybridization, if necessary, to the atoms in the templated ozone structure in 1a. 3 pts.
f. In each of the boxes below, write the approximate orbital energies and electron occupancies for the core and valence
electrons of each oxygen atom in ozone, using your answer in part (1e) as your guide. 9 pts
left oxygen
center oxygen
right oxygen
sample answer f or Be in
BeCl 2
p
sp
1s
g. Draw a 3D representation of the ozone molecule, showing the interaction of bonding and non-bonding orbitals
superimposed on the molecular skeleton, like we did in class for methane, ethane, and ethylene. 6 pts
h. Given the data for BeCl2 in part (1f), would you expect this atom to be Lewis acidic or Lewis basic? 3 pts
3. There is an instrument called an electron spin resonance (ESR) spectrometer that can detect unpaired electrons.
In which of the following species would the instrument find unpaired spin? Explain your reasoning. 5 pts
O+
O
Ne+
O2
3
F
4. Add charges to atoms in the following molecules where necessary. 5 pts
O
H3C
O
H
H
a.
b.
H
H3C
c.
H
O
H
H3C
d.
O
S
H
H
e.
5. Circle the letters of any question 4 structures that can be stabilized via resonance. Below, draw these resonance
structures and comment on their relative contribution to the electronic character of system being analyzed. 4 pts.
6. Using the line provided below each box, write the name of the functional group for any two of the question 4
structures shown. 4 pts
7. Write the expected lone pair orbital hybridization(s) in the box for each structure in question 4. 5 pts
8. What are the two distinguishing characteristics of a polar protic solvent? Provide a chemical structure to make your
point. 4 pts.
9. (a) Compute the pH of a solution prepared by dissolving one gram of chloroacetic acid (MW = 94.5 g/mol) in 1.0
liter of distilled water. The pK a for chloroacetic acid is 2.86. (b) Compute the pH of a solution prepared by dissolving
0.05 mol chloroacetic acid and 0.20 mol sodium chloroacetate in water, adjusting the volume to 500 mL. (c) If you put
chloroacetic acid into a buffer held at pH = 3.86, what is the approximate ratio of charged (chloroacetate) to
uncharged (chloroacetic acid) molecules? 11 pts (a = 4 pts, b = 4 pts, c = 3 pts)
(a)
O
OH
Cl
chloroacetic
acid
(b)
(c)
4
10. Professor Roberta Hamme (PO '93) of the Scripps Oceanographic Institute, determined that neon and argon have
very different water solubilities: Ne is about three times less soluble in water (Deep Sea Research, 2004, 51, 15171528). Please provide an explanation for the solubility differences, using annotated drawings (no essays). 5 pts
11. Add electron pairs to the following molecules and use the curved arrow notation to show how each reaction occurs.
Designate the Lewis acid and Lewis base in each reaction. And don't forget to stick the landing. 10 pts
Cl
Cl
Cl
+
Cl
Al
O
Cl Al Cl
Cl
Cl
O
S
H
+
O
O
O
H
O
S
O
H
O
H
12. The computed C-O and C-S stretching frequencies are shown for the molecule below. How would you explain the
origin of the difference in these values? 5 pts
O
S
=1700 cm
=1118
cm
(C-S)
(C-O)
1
1
13. Write down the two most reasonable resonance structures for HONC (connectivity shown below). Circle the more
important contributing structure and draw its predicted 3D structure in the usual manner, with labelled orbitals
superimposed on a molecular skeleton. 9 pts
H
O
N
C