CHEM1001
2014-J-6
June 2014
Marks
• Complete the following table. The central atom is underlined.
Species
Lewis structure
22/01(a)
8
Molecular geometry
NH3
trigonal pyramidal
SO3
trigonal planar
ICl3
T-shaped
ICl4–
square planar
CHEM1001
2013-J-2
June 2013
• Complete the following table, including resonance structures where appropriate. The
central atom is underlined.
Species
Lewis structure
Molecular geometry
N
F
F
F
F
NF3
F
N
F
Is the species
polar?
Yes
Trigonal pyramidal
S
SO2
O
S
O
O
O
Yes
V-shaped
F
F
ClF5
F
F
F
Cl
F
F
Cl
F
F
Yes
F
Square-based pyramidal
H
H
B
BH3
B
H
No
H
H
H
Trigonal planar
THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY
22/01(a)
Marks
10
CHEM1001
2012-J-3
June 2012
• Complete the following table, including resonance structures where appropriate. The
central atom is underlined.
Species
Lewis structure(s)
22/01(a)
Marks
6
Is the molecule
polar?
COCl2
yes
CS2
no
NBr3
yes
SO2
yes
• What is resonance? Give at least one example.
When two or more Lewis structures can be drawn for a molecule, the true
structure is none of the structures that is drawn, but a type of average made up
of all the resonance contributors. Some structures may contribute more than
others.
For example, in NO3–, the ion does not contain 1 double and 2 single bonds, but
is an average of the three structures shown. All of the N-O bonds are exactly the
same length and the energy of the true structure is lower than the theoretical
energy for any one of the given structures. This energy difference is known as
resonance stabilisation energy.
2
CHEM1001
2012-J-5
June 2012
• The σ-bonding in two plausible structures of ozone, O3, is shown below. Complete
each structure by adding electrons and/or π-bonds as appropriate.
Which of these geometries does ozone adopt? Give reasons for your answer.
Ozone adopts the non-cyclic structure. The cyclic structure is very strained with
bond angles of 60° instead of 109.5°, making it very unstable. In contrast, the
second structure is stabilised by resonance.
Ozone does not contain 1 double and 1 single bond. Both the O-O bonds are
exactly the same length and true structure is a sort of average of the two Lewis
structures shown. The energy of the true structure is lower than the theoretical
energy for either of the given structures. This energy difference is known as
resonance stabilisation energy.
22/01(a)
3
CHEM1001
2010-J-3
June 2010
22/01(a)
Marks
• Complete the following table.
6
Molecule
NH3
SF4
CO2
Number of bonding
electron pairs
3
4
4
Number of nonbonding electron
pairs on central atom
1
1
0
Lewis structure
H N H
O C O
H
Molecular shape
trigonal pyramidal
“see saw”
linear
• What is resonance? Illustrate your answer by using the nitrate ion, NO3–, as an
example.
When two or more Lewis structures can be drawn for a molecule, the true
structure is none of the structures that is drawn, but a type of average made up
of all the resonance contributors. Some structures may contribute more than
others.
In NO3–, the ion does not contain 1 double and 2 single bonds, but is an average
of the three structures shown. All of the N-O bonds are exactly the same length
and the energy of the true structure is lower than the theoretical energy for any
one of the given structures. This energy difference is known as resonance
stabilisation energy.
3
CHEM1001
2010-J-3
June 2010
22/01(a)
CHEM1001
2009-J-3
June 2009
Marks
• Complete the following table.
10
Species
Lewis structure
NH3
H N H
Arrangement of the
electron pairs around
the underlined atom
Geometry of
species
tetrahedral
trigonal pyramidal
octahedral
octahedral
tetrahedral
tetrahedral
linear
linear
trigonal
bipyramidal
T-shaped
H
F
F
SF6
F
S
F
F
F
_
F
BF4
–
F
B
F
F
CO2
O C O
Cl
ICl3
Cl I
Cl
22/01(a)
CHEM1001
2008-J-3
June 2008
22/01(a)
Marks
• Complete the following table.
9
Molecular formula
NH3
PCl5
BrF3
Name
ammonia
phosphorus
pentachloride
bromine
trifluoride
Lewis structure
H N H
Cl
H
Cl
P
Cl
Cl
Cl
F
F Br
F
Number of bonding
electron pairs on
central atom
3
5
3
Number of nonbonding electron
pairs on central atom
1
0
2
Molecular shape
trigonal pyramidal
trigonal
bipyramdial
‘T-shaped’
THE REMAINDER OF THIS PAGE IS FOR ROUGH WORKING ONLY
CHEM1001
2007-J-3
June 2007
Marks
• Complete the following table.
Molecular formula
9
SF6
NH3
ClF3
Name
Lewis structure
chlorine trifluoride
F
F
22/01(a)
F
S
F
F
F
F
F
Cl
H N H
H
F
Number of bonding
electron pairs on
central atom
6
3
3
Number of nonbonding electron
pairs on central atom
0
2
1
Molecular shape
octahedral
T-shaped
trigonal pyramidal
CHEM1001
2004-J-3
June 2004
 Give the formula and name of a binary ionic compound formed from the following
elements.
Formula
Name
magnesium and oxygen
MgO
magnesium oxide
barium and bromine
BaBr2
barium bromide
sodium and nitrogen
Na3N
sodium nitride
potassium and oxygen
K2O
potassium oxide
 Explain why some ionic compounds are soluble in water and usually insoluble in
hydrocarbon solvents such as kerosene.
Marks
6
2
When an ionic solid dissolves, the strong ionic bonds between the constituent
ions need to be broken (lattice enthalpy). In water, strong bonds are formed
between the ions and the highly polar water molecules to give aquated ionic
species. The energy released in this process (enthalpy of solvation) is sufficient
to overcome the lattice enthalpy and the solid dissolves. In kerosene, there is
little attraction between the ions and the non-polar solvent. The solvation
enthalpy is very small in this case, certainly not large enough to overcome the
lattice enthalpy, and so dissolution does not occur.
 Draw Lewis diagrams for the following species. Show both bonding and nonbonding pairs of valence electrons. Give the geometry of the species.
NH4+
SO2
H
N
N
O
S
H
N
Geometry: tetrahedral
Geometry: bent (~120°)
O
4
CHEM1001/CHEM1101 combined
2003-N-5
November 2003
Marks
5
 The structure of morphine is given below.
#1
N
CH3
a
b
#2
O#4
HO
#3
OH
c
Name the functional groups in morphine that have been highlighted by the boxes.
a = amine (3°)
b = alkene
c = alcohol
What are the approximate bond angles at the labelled atoms?
Atom
Bond angles
#1
N
~109.5°
#2
C
~120°
#3
C
~109.5°
#4
O
~109.5°