CHEM1901/3
2014-J-6
June 2014
• Complete the table below showing the Lewis structures and the predicted shapes of
the following species.
Species
Approximate F-X-F
bond angle(s)
Name of
molecular shape
F
109.5o
tetrahedral
F
90o, 120o and 180o
‘see-saw’
F
90o and 180o
‘T-shaped’
F
90o and 180o
T-shaped
Lewis Structure
F
SiF4
F
Si
F
F
SF4
F
S
F
F
XeF3+
F
Xe
F
XeF3–
F
Xe
Marks
8
CHEM1901/3
2014-J-7
June 2014
• (R)-Carvone is a typical terpene, a class of compounds widely distributed in nature.
On the structure of (R)-carvone below, circle all of the carbon atoms with trigonal
planar geometry.
(R)-carvone
Marks
2
CHEM1901/3
2013-J-7
June 2013
• Complete the following table on the given oxides of nitrogen. Indicate the charge on
all atoms with non-zero formal charge.
Molecule
Lewis Structure
Shape of molecule
NO2
bent
N2 O
linear
NO3
trigonal planar
THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY
Marks
9
CHEM1901
2012-J-6
June 2012
• Complete the table below showing the Lewis structures and the predicted shapes of
the following species.
Approximate
F-X-F
bond angle(s)
Name of molecular shape
NF3
109°
trigonal pyramidal
XeF3+
90°, 180°
T-shaped
XeF4
90°, 180°
square planar
XeOF4
90°, 180°
square pyramid
Formula
Lewis Structure
THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY
Marks
6
CHEM1901/3
2010-J-6
June 2010
• Toosendanin (pictured) is an ingredient from traditional Chinese medicine and is
effective as an antibotulismic agent both in vitro and in vivo. The compound can
prevent death in animals suffering from botulism and help restore normal activity.
It may also help to treat Botox overdoses in humans.
a
CH3
b
O C
O
O
O
OH
O
H3C
O
O
C O
HO
d
OH
H
c
Complete the table concerning the atoms a, b and c indicated by the arrows.
Selected
atom
Number of σ-bonds associated
with the selected atom
Geometry of σ-bonds about
the selected atom
a
3
trigonal planar
b
2
bent (V shaped)
c
4
tetrahedral
Comment on the actual bond angle exhibited by atom d as compared to electronically
similar atoms elsewhere in the molecule. Is this epoxide group likely more or less
reactive than an ether? Explain.
As the oxygen atom d makes 2 bonds and has 2 lone pairs, its electron pairs
would naturally adopt a tetrahedral arrangement to minimize repulsion. The
bond angle would then be expected to be close to 109°, as would the bond angles
for the ether groups in the molecule.
The geometrical constraint of the 3-membered epoxide ring means that the angle
is forced to be close to 60°. The electron pairs in the two C-O bonds are thus
forced to be close to one another, introducing considerable repulsion or strain.
The epoxide group is thus likely to be considerably more reactive than the ether
groups and the reactivity is likely to be such that opening of the ring is achieved.
Marks
6
CHEM1901/3
2009-J-6
June 2009
• Consider the molecule whose structure is shown below. Complete the table
concerning the atoms A, B and C indicated by the arrows.
B
A
C
CH3OCHCHCN
Selected
atom
Number of σ-bonds associated
with the selected atom
Geometry of σ-bonds about
the selected atom
A
4 (C-H × 3 + C-O)
tetrahedral
B
3 (C=C + C-H + C-C)
trigonal planar
C
2 (C-C + C≡N)
linear
Marks
3
CHEM1901/3
2008-J-5
June 2008
• Consider the molecule whose structure is shown below. Complete the table
concerning the atoms A, B and C indicated by the arrows.
C
CN
O
B
A
Selected
atom
Number of lone
pairs about the
selected atom
Number of σ-bonds
associated with the
selected atom
Geometry of σ-bonds about
the selected atom
A
2
2
bent ( ~ 109°)
B
0
4
tetrahedral
C
0
2
linear
THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY.
Marks
3
CHEM1901/3
2007-J-5
June 2007
• Consider the molecule whose structure is shown below. Complete the table
concerning the atoms A, B and C indicated by the arrows.
CH2
A
C
C
O NH2
H
B
Selected
atom
Number of lone
pairs about the
selected atom
Number of σ-bonds
associated with the
selected atom
Geometry of σ-bonds about
the selected atom
A
0
3
trigonal planar
B
2
2
bent
C
1
3
trigonal pyramid
Marks
3
CHEM1901/3
2006-J-6
June 2006
• Consider the molecule whose structure is shown below. Complete the table
concerning the atoms A, B and C indicated by the arrows.
C
A
H
H
O
C C
H C
C N C
C C
H
C NH2
H
H
B
Selected
atom
Number of lone
pairs about the
selected atom
Number of σ-bonds
associated with the
selected atom
Geometry of σ-bonds about
the selected atom
A
1
2
bent
B
0
3
trigonal planar
C
1
3
trigonal pyramidal
Marks
3
CHEM1901/3
2005-J-6
June 2005
 The structure of N-methylbenzamide is shown below. Complete the table concerning
the atoms A, B and C indicated by the arrows.
C
A
H
H
H
C
C
C
C
O
C
C
C
H
N
CH3
H
B
H
Selected
atom
Number of electron
lone pairs about the
selected atom
Number of σ-bonds
associated with the
selected atom
Geometry of bonds about
the selected atom
A
0
3
trigonal planar
B
1
3
trigonal pyramidal
C
0
4
tetrahedral
Marks
3
CHEM1901/3
2004-J-2
June 2004
 In the spaces provided, explain the meaning of the following terms. You may use an
example, equation or diagram where appropriate.
(a) anti-bonding orbital
A molecular orbital formed from 2 atomic orbitals with a nodal plane
perpendicular to the interatomic axis and between the nuclei. It is higher in
energy than the original atomic orbitals and occupation of it weakens the bond.
(b) electron affinity
The energy change that occurs when a mole of gaseous atoms or ions gains a
mole of electrons. For example, the first electron affinity of an atom is the
energy change accompanying the reaction M(g) + e–  M–(g). Electron affinities
are positive if this process is favourable and negative if this process is
unfavourable.
(c) nuclear fission
The splitting of an unstable, neutron rich nucleus into smaller nuclides and
neutrons and releasing energy in the process.
(d) electronegativity
A measure of the relative ability of elements to attract electrons towards
themselves in molecules.
(e) VSEPR model
Valence Shell Electron Pair Repulsion Theory predicts molecular shapes by
considering minimisation of the electrostatic repulsion of the electron pairs
around an atom.
Marks
10
CHEM1901/3
2004-J-4
June 2004
Marks
6
 Complete the following table.
Formula
e.g. H2O
Lewis structure
Molecular shape
Is the molecule
polar or non-polar?
O
H
bent (angular)
polar
O
sp2 hybridized C:
trigonal planar
polar
sp3 hybridized C:
tetrahedral
polar
sp hybridized C:
linear
non-polar
H
H
CH2O
C
H
Cl
H
CH2Cl2
C
H
C2Cl2
Cl
Cl
C
C
Cl
CHEM1901/3
2003-J-4
June 2003
Marks
 Complete the following table.
Molecule
Number of nonbonding valence
electron pairs about
the underlined atom
Number of valence
electron pairs about the
underlined atom
involved in -bonding.
Shape of molecule
3
SO2
PF3
XeF2
1 pair
1 pair
3 pairs
2 pairs
3 pairs
2 pairs
bent
trigonal
pyramidal
linear
Lewis structures:
F
O
S
O
F
F
P
F
Xe
F