1. [35 pts] For each of the following molecules or ions:
 draw a correct Lewis structure, indicating any nonzero formal charges. Include
equivalent resonance structures when applicable.
 Apply VSEPR theory to predict the molecular geometry around the central atom. Be sure
to state the geometrical arrangement of the atoms (as opposed to that of the bonds + lone
pairs). A 3-D sketch is not required, but you may include one to be eligible for partial credit
in the case of a wrong answer.
a.
NCl3
b.
NO3─
c.
BF4 ─
This problem continues on the next page. 
d.
NNN─
e.
IF4
f.
ONF
+
2. [35 pts] (a-e) Circle the correct answer from the choices given in the group. Explanations
are not required for this part of the problem.
a. The element with the highest ionization energy
Li
Be
Na
b. The ion with smallest radius
Cl–
Br–
I–
c. The element with the smallest second ionization energy
Ar
K
Ca
d. The element with the largest electron affinity
I
Br
Cl
e. The element most likely to form a covalent bond
Mg
B
Al
f. Rank these four ions in order of increasing size:
Mg2+ S2– Na+ Cl–
In the space below, provide explanations for any two (no more!) of the above items that you
choose. Your explanation must include the underlying physical concept(s) that lead to the
correct answer. You will not receive credit for this section if you simply write down a trend
without the underlying explanation of the trend. You will not receive credit for this section if
you simply state that a trend is due to a noble gas or full shell being stable.
3. [18 pts] The CH3+ molecular ion is a reactive species that participates in many
organic processes. The carbon atom in this ion does not obey the octet rule.
a. Draw a Lewis structure for CH3+, indicating appropriate formal charge.
b. Use VSEPR theory to determine the name of the molecular geometry of CH3+,
and draw the molecular geometry accurately.
c. Specify the type of hybridization for the C atom in CH3+. Draw an energy
level diagram showing this hybridization, along with appropriate electron
occupancy for the C atom in CH3+. Include all core and valence electrons.
d. Show the orbital overlaps (with electron occupancy) resulting from the
hybridization in part c.
e. Consider one of the three hydrogen atoms approaching the carbon atom when
the bonding occurs. Calculate the approximate Zeff experienced by the
hydrogen electron due to the carbon.
You may use the reverse of this page if needed for any part(s) of this question.
4. [12 pts] The He atom has the highest ionization energy of any element.
a. State the value of Zeff for H and then for He (a whole number in each case)
and explain how Zeff influences the relative ionization energies of H and He.
b. Careful calculations show that Zeff for He is not a whole number, but it differs
from a whole number by 0.3. Would you expect the actual Zeff for He to be 0.3
greater than the value you wrote in part (a) or 0.3 less than the value you
wrote in part (a)? Explain your reasoning.
c. Does He or Ne have the higher Zeff? Does this comparison show why He has
the higher ionization energy? Explain why or why not.