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CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
Chapter 1
Science in context
01
71
81
Coursebook answers
Si
r:
This section touches upon the development of
the atomic theory through the ages. But until the
latter part of the last century most people thought
that the idea of tiny machines made up of a few
atoms was science fiction. With the advent of
nanotechnology, these ideas are becoming a step
closer.
Ma
he
bu
l
Tiny clusters of atoms are useful for catalysts
because they have a much larger surface area
and so the catalysis can be much quicker (link
with reaction rate at IGCSE level). In recent
years, chemists have been designing ‘tailor made’
catalysts, especially zeolites (a type of silicate with
AlO4 units replacing some of the SiO4 units), of
precise dimensions with tiny pores in which the
surface area is increased dramatically. These can
also be modified to bond other catalyst particles
such as platinum and allow a vast increase in the
catalytic surface area.
Nanoclusters of atoms can be made on a cold
surface simply by evaporating a metal for example
and then letting it condense onto the cold surface.
Students may realise that the substance which is
being condensed needs to be spread out so that
the particles can separate. This can be done by
evaporating a metal for example, in a stream of
inert gas such as helium. The gas dilutes the metal
and so makes it more likely that small groups of
atoms can cluster together when they condense on
the cold surface.
Encourage students to think about things in
everyday life that have already been scaled down,
e.g. hint about mobile phones. Scientists already
have the means to move clusters of atoms around
on specially prepared surfaces. Tiny switches and
wires can be made from groups of atoms. Tiny
magnets and electronic devices could be made.
Microscopic molecular cages could be used to
deliver cancer drugs to specific places in the body.
Clusters of atoms or small molecules could be
used to ‘cage’ radioactive atoms such as radon.
A lower dose of radioactivity is therefore used
rather than a (directed) beam of more intense
radioactivity which may damage surrounding
cells. The caged molecules could be conveyed to
the cancer cells by attaching an antibody to the
outside of the molecule. This would result in a
more targeted treatment. Disadvantages may be
that the body reacts to the unusual molecule in
the bloodstream and unwelcome side-effects may
be felt. If antibodies are not attached or become
detached or become denatured then the caged
molecules have no target in the body. So the
radioactivity may harm healthy cells.
Students are asked to suggest more ideas for
nanomachines. These could include nanomagnets,
nanoswitches, nanorobots and nanomotors.
Self-assessment questions
1
a
b
2
i
Protons are deflected towards
the plate / move towards the
plate; because unlike charges are
attracted to each other.
ii
Neutrons are not deflected;
because neutrons have no charge /
zero charge / are uncharged.
Electrons; because of the charged
particles it has the least mass / has a
lower mass than the proton.
vanadium-51: electrons = 23,
neutrons = 28
Strontium-88: electrons = 38,
neutrons = 54
phosphorus-31: electrons = 15,
neutrons = 16
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b
44
20
Ca
c
58
26
Fe
d
110
46
a
18
b
10
c
10
d
28
a
Pd
electrons 36; protons 35; neutrons 46
b
electrons 55; protons 58; neutrons 78
b
Exam-style questions
i
protons = 5
[1]
ii
neutrons = 6
[1]
iii
electrons = 5
[1]
bu
l
Isotopes are atoms of the same
element with different nucleon
numbers / mass numbers / different
numbers of neutrons.
Ma
he
2
a
i
ii
iii
c
[1]
[1]
charge = −1
[1]
mass = 1
[1]
charge = zero
[1]
mass = 1
[1]
charge = +1
[1]
i
ii
51
70
c
i
ii
Zr
6
[1]
atomic number = number of protons
(in the nucleus);
[1]
Mg = 12 protons, 12 electrons,
12 neutrons
[1]
Al = 13 protons, 13 electrons,
14 neutrons
[1]
e
it would not be oxygen / it would be
another element / oxygen can only
have 8 protons
[1]
The mass of an electron is negligible.
[1]
[Total: 13]
4
a
b
[1]
[1]
Proton has positive charge, and
like charges repel / opposite
charges attract.
or negligible]
[allow
number of positively charged protons
= number of negatively charged
electrons
[1]
f
[1]
It is deflected / bends away from
the anode (or positive plate), or
towards the cathode (or negative
plate), or downwards.
1
2000
1
1836
d
[Total: 10]
91
40
b
d
mass =
1
1836
electrons are negative with relative
charge of −1 and relative mass of
nucleon number = number of protons +
number of neutrons
[1]
Si
r:
a
c
[1]
neutrons are neutral with relative
charge of zero and relative mass of 1; [1]
6
b
containing protons and neutrons;
protons are positively charged with relative
charge of +1 and relative mass of 1;
[1]
C (number of electrons in each atom)
a
[1]
electrons outside the nucleus in energy
levels;
[1]
5
1
positively charged nucleus;
65
Br
81
81
35
71
4
3
a
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CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
c
d
Isotopes are atoms of the same
element with different nucleon
numbers / mass numbers / different
numbers of neutrons.
[1]
both have 92 protons;
[1]
both have 92 electrons
[1]
uranium-235 has 143 neutrons;
[1]
uranium-238 has 146 neutrons
[1]
90
[1]
[1]
[Total: 6]
5
a
[1]
no deflection / go straight through;
[1]
neutrons have no charge
[1]
[Total: 7]
b
number of protons = 17 and 17
[1]
number of electrons = 17 and 17
[1]
number of neutrons in chlorine-35
= 18; in chlorine-37 = 20
[1]
the chlorine-35 isotope is more
abundant;
[1]
the weighted average is nearer 35
than 37
[1]
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6
Coursebook answers
i
it has more protons than electrons [1]
ii
it has 17 protons and 18 electrons /
it has 1 more electron than protons [2]
65
c
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CAMBRIDGE INTERNATIONAL AS & A LEVEL CHEMISTRY: COURSEBOOK
[Total: 8]
Ma
he
bu
l
Si
r:
01
71
Chapter 1
81
[it has more electrons than
protons for 1 mark]
3
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