Term test #2 (50 points)
Tuesday March 8, 2010
You have 50 minutes to complete this test and 7 questions.
A calculator and periodic table may be used as required.
Name:____________________________________
Student ID________________________________
Plank’s constant
h= 6.626 × 10−34 Js
Speed of light in vacuum
c= 3.0×108m/s
Avrogadros number
A= 6.022×1023 mol-1
Charge of an electron
e=1.602×10-19 C
2
Chem 222 Intro to Inorganic Chemistry
Question
Total Mark
1+2
12
3
5
4
13
5
4
6
9
7
6
Total
Grade
Chem 222 Intro to Inorganic Chemistry
3
1. (9 points) 8 points Fill in the blank with the appropriate word, phrase or reaction.
a) The formula for a superoxide is ____O2-___ and the formula for an oxide is___O2-____.
b) The first compound synthesized that contained a noble gas is ___ Xe+[PtF6]−____________.
c) The reaction associated with the energy of the second electron affinity of S is ___S- + e --->_S2d) The allotrope of phosphorus that glows green in air and is highly reactive and poisonous is known as
_________white phosphorus or P4___________.
e) The order of the bonding and antibonding MO’s arising from the p AO’s in F2 is _______ σ π π* σ* .
f) Sulfur has over 30 solid state allotropes, of these the chemical formula for the most common is__S8______.
_______plastic or amorphous or Sn_____ can be produced by melting sulphur and then quickly cooling it.
g) Place the following in order of their radii (smallest to largest) Na, S2- Mg2+, Na+ Cl-, _____ Ca2+, Na+, Na,
Cl-, S2- _____
2. (4 points) Chose the element or compound that has the higher melting point, state the type of bonding
responsible and draw a clearly labeled picture to illustrate the bonding involved.
KCl
vs MgO
MgO ionic bonding
-images discussed in class-
Ca vs Mg
Mg metallic bonding
[The answer I was actually looking for: For metallic bonding one would expect Mg to have the higher melting
point as it is smaller, but due to its slightly semimetal character the metallic bonding is not as strong for Mg as
one would expect, therefore Ca has the higher melting point (as can be seen on the periodic table). Sadlynoone wrote this, so I had to give full marks for a reasonable explanation for either.]
-images discussed in class-
Chem 222 Intro to Inorganic Chemistry
4
3. (5 points) CN- is a common pseudo halogen ligand. The order of filling of the 2p MO’s of CN- is π2p, σ2p,
π*2p, σ*2p.
a) Construct a filled energy level diagram that includes all the bonding and antibonding orbitals of the
molecule and the atomic orbitals. Be clear on their relative energies and label all orbitals with the specific
AO’s from which they were derived.
b) How would this compound react if placed in a magnetic field?
Chem 222 Intro to Inorganic Chemistry
5
a)notes
-diagram was worth 4 points with subtractions for the following
- N atomic orbital must be lower in energy than C atomic orbitals (-1 if same height).
-orbital must be labeled with specific AO from which they were derived (-1 if not labeled, -1/2
if pz , px etc not specified)
- π2p has two orbitals, σ2p has one orbital (-1 if backwards)
-CN- donates one extra electron (-1 if electron missed)
-N and C electron counts must be correct (-1 if incorrect, but it was fine if the extra electron
from the molecule was in one of the AO’s)
b) As all electrons are spin paired, this material is diamagnetic and would be slightly repelled by a magnetic
field.
-a diagmagnetic material will be slightly repelled by a magnetic force, a paramagnetic material
would be attracted. The points awarded based on correct magnetism for MO drawn by student, so an
incorrect MO could still get full marks. (1 point total, ½ point awarded if magnetism named but its
behavior was not described)
Chem 222 Intro to Inorganic Chemistry
6
4. (13 points) For the following crystal structures
a)
Identify the NaCl crystal structure and calculate the number of Na ions in the unit cell (show all
working and label all types of Na ions in the unit cell).
b)
i) Identify the CaF2 crystal structure. Identify the anion and cation and give the coordination number of
each.
ii) Give the general Born-Lande equation for the calculation of lattice energy.
ii) Calculate the lattice energy of CaF2 in kJ/mol. The Madelung constant is 2.519. The Born exponent
is 8. The radius of Ca2+ is 114 pm, the radius of F- 117 pm is and 4πε0 = 1.112 × 10−10 C²/(J·m).
a) Na is the smaller spheres
12 edge sites × 1/4 = 3
1 center site × 1 = 1
Total = 4 ions
b) i) coordination number of F is 4, coordination number of Ca is 8
ii)
iii) 2652 kJ/mol
Chem 222 Intro to Inorganic Chemistry
7
5. (4 points) Draw the bonding and antibonding orbitals that you would expect to arise from a 2pz-3pz
interaction. Discuss the bond strength in comparison to a 2pz-2pz interaction.
-a difference in size between the 3p and 2p AO should be obvious
-the orbitals must be aligned on the z axis (for bonding, this is as shown)
-a lopsideness in the resulting MOs was correct, but no marks were taken off if not present.
The bond strength would be weaker than a 2p-2p interaction (or a 3p-3p interaction) as the overlap (both
energetically and physically) is not as good.
8
Chem 222 Intro to Inorganic Chemistry
6 (9 points) Answer THREE of the following FOUR questions and clearly indicate which ones were chosen.
This question continues onto the next page.
a) Fill in the following table for ionic compounds with a 1:1 stoichiometry
cation:anion
coordination number of coordination geometry of crystal structure
radius
cation
cation
0.732-0.999
8
cubic
CsCl
0.414-0.732
6
octahedral
NaCl
0.225-0.414
4
tetrahedral
Zn blende
b) In the Born-Haber cycle, identify and define the processes that are always endothermic (require energy to
be put into the system).
ΔaH° (M,s) : enthalpy of atomization for the solid metal, the energy associated with removing an atom from
the solid metal and bringing into the gas phase, analogous but not identical to the energy for boiling a
substance
nΔaH°(X,s) : enthalpy of atomization for the halogen: energy associated with breaking the X-X bond,
endothermic as energy must be applied to break a bond
∑ IE (M,g) : ionization energy: energy to remove an electron (or series of electrons depending on the final
oxidation state required) from the metal.
For your interest
- ΔlatticeH° (MXn,s) is always a large exothermic value, the separated ions in the gas phase are in an unstable
state (actually impossible to form in significant concentrations) and will join together with a large release of
energy.
9
Chem 222 Intro to Inorganic Chemistry
- nΔEAH (X,g) the first electron affinity enthalpy is always exothermic (except possibly for the noble gases
which have a near zero value that may be slightly endothermic) while the second and subsequent electron
affinities are exothermic.
- ΔfH° (MXn,s) the overall enthalpy of the reaction can be exothermic or endothermic, depending on the other
values.
c) Using chemical equations, describe the industrial production of sulphuric acid from elemental sulphur.
S8 + 8O2  8SO2 (elevated temperatures)
2SO2 + O2 (V2O5 catalyst and heat)  2SO3
SO3 + H2SO4  H2S2O7
H2S2O7 + H2O  2H2SO4
d) Fill in the following diagram with the gas flow, electron flow, proton flow and relevant chemical reactions
and where they occur for a H2/O2 fuel cell.
80° C
2(H2
2H+ + 2e-)
O2 + 4H+ + 4e-
2H2O +
Chem 222 Intro to Inorganic Chemistry
10
7. (6 points) 5 points Match the correct chemicals from the following list with the descriptions. Please choose
only one chemical for each description. HI, H2SO4, red P, KCl, Br2, HF, white P, black P, Po,Te, O2, O3
Strong acid HI [H2SO4 was also accepted, HF is a weak acid]
Biprotic acid H2SO4
Ingredient in modern matches red P
Crystallizes in the NaCl structure KCl
Semimetal Te
Crystallizes in a simple cubic crystal structure Po (only element to do so)