Chem 130 – Second Exam
Name_______________________________
On the following pages you will find seven questions covering varies topics ranging from the structure of molecules, ions, and solids to different models for explaining bonding. Read each question
carefully and consider how you will approach it before you put pen or pencil to paper. If you are
unsure how to answer a question, move to another; working on a new question may suggest an approach to the one that is more troublesome. If a question requires a written response, be sure that
you answer in complete sentences and that you directly and clearly address the question.
Partial credit is willingly given on all problems so be sure to answer all questions!
Question 1 _____/32
Question 5 _____/10
Question 2 _____/10
Question 6 _____/10
Question 3 _____/10
Question 7 _____/18
Question 4 _____/10
Total _____/100
Potentially useful equations and constants:
c = λν
E = hν = hc/λ
⎛ 1
1
1
= 1.09737 × 10 − 2 nm⎜⎜ 2 − 2
λ
⎝ n1 n2
KE = hν – W
FC a = Va − N a −
Ba
2
𝑉∝
⎞
⎟⎟
⎠
𝑄! 𝑄–
𝑑
OX a = Va − N a − Ba × (0 if least EN; 1 if most EN)
⎛
EN a
δ a = Va − N a − B a ⎜⎜
⎝ EN a + EN b
h = 6.626×10–34 Js
⎞
⎟⎟
⎠
c = 2.998×108 m/s
NA = 6.022×1023 mol–1
Also available on separate handouts are a table of electronegativity values based on average valance
electron energies, a table of packing possibilities based on relative sizes of cations and anions, and a
periodic table.
Problem 1. For each of the following molecules or ions, draw any one valid Lewis structure of your
choosing (it need not be the “best” structure). Annotate your structure by indicating the formal
charge on each atom. Finally, give the name for the bonding geometry around the underlined central
atom, predict whether the molecule or ion is polar (P) or non-polar (NP), and provide the idealized
bond angle for the stated bonds.
Molecule or
Ion
Lewis Structure
Bonding
Geometry
Polar or
Non-Polar?
Ideal Bond
Angle for …
…an F–C–Cl
bond is….
CCl2F2
…an O–I–O
bond is….
IO2F2–
…a Cl–I–Cl
bond is….
ICl4–
Bond angle for
an F-Xe-F
bond is…
XeOF4
Problem 2. The element Z forms the molecular compound ZBr3 with a trigonal pyramidal electron
domain geometry. Identify one example of an element that could be Z. In no more than three sentences, clearly explain your reason for picking this element.
Problem 3. Consider the molecules and ions listed below. The underlined central atoms in three of
these species use the same type of hybrid orbitals to form bonds with the remaining atoms; the
fourth species uses a different set of hybrid orbitals. Circle the species that is different and indicate
the type of hybrid orbitals it uses. In no more than three sentences, clearly explain your reason for
picking this species.
NO2–
CO32–
BF3
NH3
Problem 4. Shown to the right is the molecular orbital
diagram for the molecule BO. Complete the molecular
orbital diagram by filling in the electrons for each atom
and for the molecule. Based on your molecular orbital diagram, what is BO’s bond order? Is BO a paramagnetic or a
diamagnetic compound (circle your answer below)? In no
more than three sentences, clearly explain the reasons for
your answers.
The bond order for BO is __________.
BO is: paramagnetic
diamagnetic
Problem 5 The following compounds are generally considered covalent: HCl, ICl, and SCl2. As we
have seen, a pure covalent bond is rare. Rank these compounds from the one showing the least ionic
character to the one showing the greatest ionic character. Place your answers in the table and show
any relevant work and/or explanation in the space below the table.
least ionic character
←→
greatest ionic character
Problem 6. The following compounds have similar ionic characters, but differ in the degree of metallic and covalent character: MgH2, BaSi2 and ZnS. Rank these compounds from the one showing
the most metallic character to the one showing the most covalent character. Place your answers in
the table and show any relevant work and/or explanation in the space below the table.
most metallic character
←→
most covalent character
Problem 7. Shown below are three cross-sections through the unit cell of calcium titanate, also
known as the mineral perovskite.
What is the empirical formula for calcium titanate based on this unit cell? Be sure to clearly explain
how you arrived at this formula.
The titanium ion can be considered to sit in two types of holes – a hole in a lattice defined by calcium ions and a hole in a lattice defined by oxygen ions. For each, state the type of hole in which the
titanium ion sits and what percentage of these holes are filled.
For a lattice of calcium ions, titanium sits in a(n) ______________________ hole and
occupies __________ % of these holes.
For a lattice of oxygen ions, titanium sits in a(n) ______________________ hole and
occupies __________ % of these holes.
To how many oxygen ions is each calcium ion coordinated? Briefly explain how you arrived at your
answer in no more than three sentences and/or with an appropriate sketch.