Chemical Bonding - Suggested Solutions
Topic 3 : Chemical Bonding
ACJC/P3/Q2a
1.
I
x x xx
x I
xx
I
Linear
AJC/P2/Q1b(i)
Al2O3 has a giant ionic lattice structure with strong electrostatic forces of attraction
2.
between oppositely charged Al3+ and O2- ions.
SO2 and SO3 have simple molecular structures with weak van der Waals forces between
the molecules.
ACJC/P2/Q2d(i)
3.
•
•
•
Br2 has a smaller electron cloud size than I2.
electron cloud of Br2 is less polarisable
weaker van der Waals’ forces between the molecules
less energy is required to overcome the interaction between Br2 molecules, leading to a
lower boiling point.
AJC/P3/Q5b,c
4(a) More energy is needed to overcome the strong hydrogen bonds between HF molecules,
as compared to the weaker permanent dipole permanent dipole interactions between
HCl molecules, hence HF has a higher boiling point than HCl.
HI has a higher boiling point compared to HCl, as it has a larger electron cloud, which is
more polarisable, leading to stronger and more extensive van der Waals forces that
require more energy to overcome.
(b)
BrF3 has 2 lone pairs and 3 bond pairs around the central Br atom, which leads to a Tshape geometry. In BrF2+, there are 2 lone pairs and 2 bond pairs around the central Br
atom which leads to a bent (V-shape) geometry.
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Chemical Bonding - Suggested Solutions
SbF5 has 5 bond pairs around the central Sb atom, which leads to a trigonal
bipyramidal geometry. In SbF6-, there are 6 bond pairs around the central Sb atom,
which leads to an octahedral geometry.
DHS/P2/Q2c
5.
DHS/P3/Q4b,c
6(a) SiO2 has a giant molecular structure with extensive covalent bonding in a giant
three-dimensional structure.
PbO2 has a giant ionic structure. In the solid state, the ions can only vibrate about
fixed positions.
(b) A large amount of energy is required to overcome the strong electrostatic forces of
attraction between the cations and sea of delocalised electrons.
HCI/P3/Q1a(ii)
7.
Shape with respect to each P: Trigonal pyramidal; Bond angle: 107o
HCI/P3/Q1d(i)
8. Both Cl2 and I2 have simple molecular structures, and exist as diatomic molecules with
weak van der Waals forces existing between molecules.
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Chemical Bonding - Suggested Solutions
I2 has a bigger electron cloud than Cl2 and hence, stronger and more extensive van der
Waals forces between the molecules. Therefore I2 is less volatile than Cl2.
HCI/P3/Q3a
9(a)
M.p. /oC
Melting
point /oC
Na
Mg
Al
Si
P
Si
S
Cl
Ar
High melting point from Na to Al as they exist as giant metallic structures with strong
metallic bonds of increasing strengths due to smaller cationic radius and increased
number of delocalized electrons.
Very high melting point for Si as it exists as a giant covalent structure with an
extensive network of strong covalent bonds. These strong bonds require a lot of
energy to break before melting can occur.
Low melting point from P to Ar as they exist as simple molecular structures,
consisting of discrete molecules with weak van der Waals forces between the
molecules. Melting point decreases from S8 > P4 > Cl2 > Ar because the size of the
electron clouds decreases from S8 > P4 > Cl2 > Ar, such that weak van der Waals
forces are weaker.
IJC/P2/Q1b
10. No. Although ionic bonds between K+ and Cl- ions are broken in the boiling of KCl, it is
weak van der Waals forces between tetrachloromethane molecules that are broken
during boiling, not covalent bonds within tetrachloromethane molecules.
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Chemical Bonding - Suggested Solutions
IJC/P2/Q2a(ii)
11. SiO2 exists as a giant covalent structure with an extensive network of strong covalent
bonds. These strong bonds require a lot of energy to break before melting can occur,
hence SiO2 has a very high melting point.
IJC/P2/Q2b(i)
12.
JJC/P2/Q1a(i)
13.
O
S
O
O
S
O
Bent/ angular/ v-shape
O
trigonal planar
MI/P3/Q4b
O
14.
H
H
O
Shape is bent, hence bond angle = 104.5o
MJC/P3/Q2c(I,ii)
15(i) Iodine has a large enough atomic size to accommodate the number of O atoms
surrounding it in IO53- and IO65- .
5-
(ii)
x
x
x
O
x
x
x
x
x
O
x
x
x
x
x
O
x
x
x
xx
x
x
I
x
O
x
O
x
O
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
x
xx
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Chemical Bonding - Suggested Solutions
NJC/P3/Q1a,b(i)
16 (a) Electronegativity is defined as the ability of an atom to attract bonding pair of
electrons to itself in a covalent bond.
The oxygen atom is more electronegative than the nitrogen atom.
•
•
•
Oxygen has a greater nuclear charge than Nitrogen atom.
They have similar shielding/screening effect.
Effective nuclear charge of O atom is greater than that of N atom; it will attract the
bonding electrons more strongly.
(b) (i) x
x
xx
xx
xx
N N xx
x
x
xx
x
N xx
xxN x O
Shape of N2O is linear. Bond angle is 180o.
NJC/P3/Q4a
17.
-
O
2+
Ca
2
xx
O Ix xx O
o
x
x
NYJC/P3/Q1c
18.
MgO > NaF > H2O > CH3NH2 > CO2
CO2 have simple molecular structure consisting of CO2 molecules held together by van der
Waals forces.
CH3NH2 and H2O have simple molecular structures consisting of CH3NH2 and H2O
molecules held together by stronger hydrogen bonds.
H2O has 2 lone pair hydrogen units while CH3NH2 has 1 thus H2O has higher boiling point.
NaF and MgO have ionic structures consisting of oppositely charged ions held together by
strong electrostatic forces. MgO has higher boiling point because it has higher ionic
charges than NaF.
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Chemical Bonding - Suggested Solutions
NYJC/P3/Q5a
19.
Cl x
x x
x
Cl
N
x x
Cl
3 bp 1 lp
Trigonal
pyramidal
Cl
B
x
Cl
x
Cl
3 bp 0 lp
Trigonal
plannar
NCl3 and BCl3 have simple molecular structure but NCl3 has a net overall dipole moment thus
the molecules are held together by van der Waals forces due to permanent dipoles.
BCl3 has no overall dipole moment thus the molecules are held together by van der Waals
forces due to induced dipoles and therefore require less energy to break the bonds.
PJC/P2/Q1b
20.
NaCl – giant ionic lattice structure with strong electrostatic forces of attraction between
oppositely charged Na+ and Cl- ions
AlCl3 – simple covalent/molecular structure
– weak temporary induced dipole-induce dipole attraction between molecules.
PCl5 – simple covalent/molecular structure
– permanent dipole - permanent dipole attractions between molecules.
AlCl3 exist as dimers, with stronger instantaneous dipole-induced dipole (due to greater no. of
electrons) than permanent dipole - permanent dipole attractions of PCl5.
Hence m.p. of AlCl3 is higher than PCl5.
PJC/P2/Q2b(ii)
21.
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Chemical Bonding - Suggested Solutions
PJC/P3/Q2b
22.
SAJC/P2/Q2b
Carbon
23(ii)
Shape
Bond angle
C1
Trigonal planar
120°
C2
tetrahedral
109°
SAJC/P2/Q3a
24(a) (i) In water, ethanoic acid molecules form intermolecular hydrogen bonds with water
molecules and exist as CH3CO2H. Hence its Mr is 60.
In a non-aqueous solvent, hexane, the id-id interactions between ethanoic acid and
hexane is weaker so ethanoic acid molecules dimerise by forming stronger
intermolecular hydrogen bonds with ethanoic acid molecules. Hence its Mr is twice that
of CH3CO2H and becomes 120.
∂+
∂-
H–O
O
CCH3
CH3C
∂+
O–H
Hydrogen bond
∂-
:O
SAJC/P3/Q1b
25.
Compound A is held by hydrogen bonding.
Compound B is held by weak induced dipole-induced dipole interactions (id-id)/weak
VDW. Less energy is needed to overcome the weaker id-id interactions in B.
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Chemical Bonding - Suggested Solutions
Although Compound C does not have H-bonding, having more electrons causes
stronger id-id (or VDW, but not pd-pd) which compensates for the absence of H-bonding.
Hence more energy is required to overcome the intermolecular forces of attraction in C.
SRJC/P3/Q2a(i)
26. MgO
has a giant ionic lattice structure
large amount of energy is needed to overcome the strong electrostatic forces
of attraction between oppositely charged ions.
has a high boiling point
P4O6
has a simple molecular structure
small amount of energy is needed to overcome the weak intermolecular van der
Waals’ forces of attraction
has a low boiling point
TJC/P2/Q1b
27(i)
O
Cl
Cl
P
Cl
Cl
Cl
POCl3
Tetrahedral
(ii)
●
P
Cl
Cl
Cl
PCl5
Trigonal bipyramidal
POCl3 and PCl5 both are simple discrete molecules with weak van der Waals’ forces of
attraction between the molecules (or POCl3 has permanent-dipole-permanent-dipole
interactions while PCl5 has induced-dipole-induced-dipole interactions between
molecules).
PCl5 has a much larger Mr than POCl3, and therefore a larger electron cloud that is more
easily distorted, giving rise to larger partial charges, resulting in stronger van der Waals’
forces.
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Chemical Bonding - Suggested Solutions
TJC/P2/Q1a
28. Phosphorus, sulphur and chlorine all have simple molecular structure with weak
instantaneous dipole-induced dipole forces between the molecules. Sulfur exists as S8
molecules, while phosphorus exists as P4 molecules and chlorine exists as Cl2 molecules.
Hence, sulphur has the strongest intermolecular instantaneous dipole-induced dipole
forces as its molecules have the biggest electron cloud which makes them more
polarisable.
TJC/P3/Q1a
29. AlF3 has a giant ionic lattice structure with strong electrostatic forces of attraction between
oppositely charged Al3+ and F- ions. AlCl3 has a simple molecular structure with weak van
der Waals forces between its molecules. More energy is needed to overcome the strong
ionic bonds in AlF3 than the weak intermolecular forces in AlCl3 hence AlF3 has a much
higher melting point.
TPJC/P2/Q1b(iii)
30.
TPJC/P3/Q2d
31.
VJC/P2/Q3a(i), c(i)
32(a)(i) NaCl is an ionic compound with giant ionic structure held by strong electrostatic
forces of attraction between the oppositely charged Na+ and Cl- ions.
Silicon tetrachloride has a simple molecular structure. The molecules are nonpolar and held by weak induced dipole-induced dipole attractions which can be
easily broken during melting.
Since ionic bonds are much stronger than id-id, NaCl melts at a much higher
temperature.
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Chemical Bonding - Suggested Solutions
(c)(i)
Cl
Cl
Al
Cl
Cl
Al
Cl
Cl
VJC/P2/Q3d
33.
Formulae of ions: [ClO2]+ and [ClO4]-
VJC/P3/Q3b
34(i) The molecular formulae suggest that the structure of chlorosulfonic acid is derived from
that of sulfuric acid, with 1 –OH group being replaced by –Cl.
Hence the extent of hydrogen bonding is less between chlorosulfonic acid molecules
which explains its lower boiling point.
(ii)
O
O
109O
O
S
H
O
O
O S O
O 105
O
H
VJC/P3/Q3e
35(i) As Mg is less electronegative than S, the electronegativity difference between Mg and F
is larger compared to that between S and F.
Hence MgF is ionic whereas SF2 is covalent.
(ii)
MgF2 has a much higher melting point that SF2.
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Chemical Bonding - Suggested Solutions
OR MgF2 conducts electricity in the molten state but SF2 does not conduct electricity in
any state.
(iii) To form MgF4, Mg2+ has to lose two more electrons from the penultimate shell which
results in a prohibitively high amount of energy required.
This cannot be compensated by the energy evolved from the formation of the ionic lattice
of MgF4.
YJC/P2/Q1b(ii)
36. Hydrogen bonding exists between HF molecules
YJC/P2/Q2a
37.
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Chemical Bonding - Suggested Solutions
YJC/P3/Q5a
38.
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