IA Inorganic Chemistry
St Anne’s and Oriel Colleges
TT 2017
Periodic Trends and the Main Group
Suggested reading:
• Chemistry of the Elements, Greenwood & Earnshaw
• Advanced Inorganic Chemistry, Cotton & Wilkinson
Questions:
(i) Review the origin and consequences of relativistic effects in the chemistry of the main group
elements. Illustrate your answer with suitable examples.
(ii) What is the alternation effect? What is the inert pair effect? Give examples of both.
Homonuclear multiple bonds
(iii) Discuss the following data for homonuclear bond energies (kJ/mol):
Mean bond dissociation enthalpies (kJ/mol)
p
p
C-C
335
295
160
Si-Si
195
O-O
395
145
P-P
120
Ge-Ge
165
p
N-N
120
200
S-S
145
270
As-As
175
350
120
155
Se-Se
210
125
p-bonding component largest for 1st row; low -bond strength for N, O
(iv) For both groups 13 reflects
and 14,
the trends in (i) s/p energy gap and (ii) s/p promotion
lonesketch
pair repulsions
energies as a function of principal quantum number. Rationalise the differences between these
Elemental structures reflect balance between the two bonding types –
two functions.
for 1st row + p > 2 , but reverse true for 2nd row
(v) Consider the family of compounds R2 E=ER2 , where E is a group 14 element and R is an alkyl
group. Comment on the observation that the geometry of these molecules is planar when E =
C, but not when E = Ge or Sn. Describe the nature of the bonding in these various cases.
(vi) What is a second-order Jahn Teller (SOJT) distortion? Discuss the relevance of SOJT distortions to the emergence of stereoactive lone pairs in the (N − 2) oxidation state of main group
elements. Using the group 14 monochalcogenides as an example, explain the role of anion
orbitals in mediating SOJT distortions of main-group solids.
coupling constants of free ethene and ethene coordinated to a metal centre:
(a) The mean bond enthalpies (kJ mol–1) involving some elements E of Group 15:
Bond length/pm
N
P
As
KPtCl3(C2H4)
137
E-E
167
209
180
IA Inorganic Chemistry
Pt(PPh3)2(C2H4)
143
St Anne’s and Oriel
Colleges 945
TT 2017
E≡E
493
380
Fe(CO)4(C2H4)
146
E-H
391
322
297
(vii) Explain the observation that in the solid-state structures
of PX5 (X = Fl, Cl, Br), the
Os(CO)4(C2H4)
149
7.
AnswerE-O
either partspecies
A or
B.
phosphorus-containing
adopt
structures
with
the
following
point groups:
214
360
326
Os2(CO)8(C2H4)
152
A. For THREEE-F
of the following
series of compounds (i)487
– (vi) describe their structures and
278
PF5 has D3h490
symmetry;
indicate how
they
reflect
the chemistry of
the element in bold. Note that only an empirical
Free
C2H
134
4
PCl
both Oh and 309
Td symmetry;
5 shows
322
formula hasE-Cl
been given for313
some
compounds.
PBr5 1has
symmetry.
J(1H,T13dC)/Hz
Pt(Ph3P)2(C2H4)
146
What structures
observed for the corresponding
As-, 1Sb-,
and
Bi-containing compounds?
1
13
(b) The (i)
bondare
lengths
bond
MgO of the carbon-carbon
TiO
NbOand the J( H , C) NMR spin-spin
Free C
coupling
constants
of free ethene157
and ethene coordinated to a metal centre:
2H4
(viii) Discuss the following
data regarding
bond angles
in AH2 and X2 O molecules (given in degrees).
(ii)
TiS2
MoS2
FeS2
Comment, where appropriate, onBond
the length/pm
wider significance of any trends shown:
(c) The bond angles in AH2 and X2O molecules (in degrees):
(iii)
BaO
AgO
PbO
KPtCl3(C2H4)
137
AH2
H-A-H bond angle
XO
(iv)
CrCl2
MoCl2
PdCl2 2
Pt(PPh3)2(C2H4)
143
BeH2
180
Me2O
(v)
CO2
SiO2
PbO2
Fe(CO)4(C2H4)
1464
BH
131
(H3Ge)2O
GaCl2
CdCl2
SnCl2
DCHC 2792 (vi)2
Os(CO)4(C2H4)
149
NH2
103
[(Cl5Ru)2O]6–
Os2(CO)8(C2H4)
OH2
104.5
B.
X-O-X bond angle
110
148
180
152
Free C2H4
Answer both parts (i) and (ii)
134
Pt(Ph
3P)2(C
2H4)
following
metal
complexes:
146
[3 x 25/3]
1 1
(ix) Review the general
trends in structures
and allotropy of the main group elements (i.e. in their
J( H,13C)/Hz
(d) The 59Co NMR chemical shift (δ) and ligand-field splitting parameter (Δ) in the
(i)
Discuss
the
occurrence
of
isomerism
in inorganic chemistry with reference to the
elemental
forms).
following cobalt complexes:
-1
(x) Discuss the nature
of
bonding inδeach
the following
compounds.
/ppmof
Δ /cm
2+
Free C2Pd(NH
H4
157
[Ru(bipy)
[Co(en)2Br2]+
3)2Cl2
3]
K3[Co(CN)
0
3–
6]
POCl
[Ni(CN)
3 5] S4 N4
K3[Co(CO3)3]
2+33909
3+
2+
XeF
B42)]Cl
Bi
RhCl
[Co(NH
6 (s) 3)5(NO
4
3 4
5 3(py)Te
14070
17624
[20]
K3[Co(C
12930
2O4)3]
(ii) Describe
a plausible
method
for distinguishing the18153
isomers of one of the examples
given
in
part
(i).
[Co(NH3)6]Cl3
8175
22931
4
DCHC 2792
[5]
[Co(phen)3]Cl3
7080
26198
End of paper
6
DCHC 2792
5
DCHC 2792
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IA Inorganic Chemistry
St Anne’s and Oriel Colleges
TT 2017
Past paper questions:
6.
Non-metal chemistry
(2011)
Answer both parts (a) and (b).
(a)
Identify the compounds A-E in the Scheme below, accounting for
all the spectroscopic and chemical observations.
Note: The conditions specified do not necessarily indicate the
stoichiometries of the reactions, and not all side products are noted.
A Colourless gas containing only boron and hydrogen with RMM
27.6.
[2]
B Colourless volatile liquid with RMM = 63. The 1H decoupled 11B
NMR spectrum features resonances at –11.5 ppm and –55.2 ppm in
a 4:1 ratio.
[3]
C Volatile molecular solid with RMM 117.3.
[3]
D RMM = 163.6. Liquid at room temperature but crystallises below
180 K. In the solid state the infrared and Raman spectra both show
two bands in the B-Cl stretching region, none of which coincide. [5]
(b)
E Weak monobasic acid containing 17.5% boron by mass.
[3]
Rationalise the structure adopted by compound B.
[4]
Relative atomic masses: Cl = 35.5, O = 16.0, B = 10.8, H = 1.0.
XCHA 2714
7
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IA Inorganic Chemistry
St Anne’s and Oriel Colleges
TT 2017
(2015)
4.
Answer ALL parts (a) – (d).
Examine the following reaction scheme. Identify the products A−E and
write balanced equations for the reactions taking place. Account for all the
observations and spectroscopic data given below. Some of the reaction
steps may involve the formation of by-products. The scheme is not
intended to indicate the stoichiometries of the reactions.
(a)
(b)
(c)
(d)
A is a colourless liquid containing 51% Se by mass. If coupling to the
minority magnetic 77Se nucleus is neglected, the 19F NMR spectrum at
low temperatures consists of two 1:2:1 triplets of equal intensity. In the
gas phase the Se–F stretching region has four bands in both the infra-red
and Raman spectra.
[5]
B is a colourless gas with a 19F NMR spectrum (neglecting coupling to
magnetic Se nuclei) consisting of a single line. The infra-red and Raman
spectra show no common features.
[2]
Reaction of Se with elemental Cd produces a deep red solid C with the
wurtzite structure type, while reaction of Se with elemental iron produces
a black metallic solid D with the NiAs structure type.
[4]
Selenium burns in air to produce a white solid product E containing 71 %
Se by mass. In contrast sulfur burns in excess air to produce a compound
containing 40 % S by mass.
[4]
[Relative atomic masses: O = 16.0, F = 19.0, S = 32.0, Se = 79.0]
[Nuclear properties: 19F, I = 1/2, 100 %; The spins of other nuclei should
be ignored.]
End of question, turn over
A10396W1
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