Download Symmetry

Exam #3 Topics and Sample Questions
Ionic Compound Bonding and Structure
Symmetry: Identifying symmetry elements and determining point groups
Coordination Chemistry: Structures and isomerism
Coordination Chemistry: Bonding and spectroscopy
Some Questions:
Ionic Compounds
1. The formula for lattice energy, Uo, is:
Compare each term for the two salts: MgBr2 and KBr
a) Circle for which each is larger:
Z+Z-
MgBr2
or
KBr
or
same
M
MgBr2
or
KBr
or
same
(1 – 1/n)
MgBr2
or
KBr
or
same
KBr
or
same
b) Which overall do you expect to have a stronger lattice energy?
MgBr2
or
c) Which term in the equation do you think is most important in any difference between them?
d. What is the purpose of the Madelung constant?
2. The solid spheres represent O; the hollow spheres represent Ti.
What is the formula of the compound? What is the oxidation state of the Ti?
3. A Bragg’s Law question:
Symmetry
8. List the ALL symmetry elements and
point group for each of these molecules.
Rotation axes
BrF5
Point group: _____
XeF4
Point group: _____
Mirror planes
Inversion center
9. All five molecules below are planar (flat). Which two molecules have
the same point groups as this transition metal compound? Circle them
and note what the point group is here: _____
Which structure above has the Cs symmetry point group? Draw an arrow to it.
Which molecule(s) have an inversion center? Write an “i” below any that do.
Transition Metal Chemistry
10a. Consider the EDTA (ethylenediaminetetraacetic acid) anion, and the schematic of a
coordination complex it forms.
What is the coordination number of the complex? ________________
What is the denticity of the EDTA ligand? Give a word or a number. The word should not
include the phrase “poly.”
__________________
If the CH2CH2 bridge between the two N atoms was to break in the metal-bonded EDTA, the
coordination number would be ______ and the denticity would be __________________.
10b. Co(trien)(NH3)22+
three views:
Coordination Number: _________
Denticities of each ligand:
__________________________
11.
All ions exist in aqueous solution as octahedral compounds, where the six ligands are water
molecules. Consider the Cu2+ ion in water.
Considering this complex, answer the following questions:
What species is the Lewis acid?
_____________
What species is the Lewis base?
_____________
What is the donor?
_____________
What is the acceptor?
_____________
What is the charge on Cu?
_____________
What is the d-electron configuration?
_____________
12. Consider the compound, Ni(NH3)4Cl(SCN). The SCN ligand can potentially bond via the S-end or the
N-end.
a. Draw a constitutional isomer (connectivity based) of this compound.
What specific kind of isomer have you drawn?
b. Draw a stereoisomer (spatial based) of this compound.
13. Another popular ligand in transition metal chemistry is terpyridine, abbreviated “trpy.” Its organic
line structure is given below.
a. What is the maximum denticity of
this ligand?
________________
b. One compound containing trpy is shown
below: Ni(trpy)Cl3-.
How many other isomers of this compound are possible? Explain.
c. Would a similar compound that used three pyridine ligands instead of tery be more stable or less
stable?
Pyridine:
d. Here is an isomer of trpy. Is it expected to behave similarly or differently than trpy?
Explain in what ways it would be similar and in what ways it would differ.
14a. Below is a molecular orbital diagram for a transition metal compound. Label it and explain
everything you can about it. Fill in electrons if the compound were Cr(NH3)63+.
14b. How many unpaired electrons will FeCl63- have? Fill in the d-orbital portion of the MO diagram to
show how you get the answer.
15a. The metal orbital portion of MO diagrams for two complexes of Ni2+ are shown below.
a. Which has stronger metal-ligand bonding? _________
b. Which will absorb light at longer wavelengths? __________
15b. If Zn2+(aq) could be oxidized to Zn3+(aq) (it can’t, really, but if it could…) would it likely
result in a colored aqueous solution?
Recall that (aq) means the metal ion is bonded to six water ligands.
Use the molecular orbital diagram to support your answer.
15c. We discussed in class that the Mn2+ ion in aqueous solution is colorless, unlike almost all the other
transition metal ions. If Mn2+(aq) is reacted with an oxidizing agent, the solution rapidly becomes deeply
colored. Use the molecular orbital diagrams below to explain why.
15d. Explain why Re2+(aq) might be a colored solution, even though it, like Mn2+, is a d5 metal ion.
16. Determine the oxidation state and d-electron configuration on metals in coordination compounds.
Fe is Fe(CN)63Mn in Mn2(CO)9
17. Predict relative stability using the chelate effect, and explain it.
Which is more stable: Ni(NH3)62+ or Ni(en)32+?