ETV “Junior Secondary Science” Programme
“Metals”
Teachers’ Notes
Target Audience
Secondary 1 - 3
Duration
20 minutes
Production Aim
This programme is a teaching resource produced especially for enriching the
classroom teaching of the Syllabus for Science (Secondary 1 – 3) prepared by the
Curriculum Development Council (1998).
The content of the programme serves to illustrate the following parts of the
Syllabus:
“Unit 13: Metals
13.2 – How to obtain metals
13.3 – Properties and uses of metals,
13.4 – Making metals more useful, and
13.5 – Environmental problems associated with the disposal of used metals”
Key Points
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Introduction to the history of using metals and the ways of extracting metals;
Explanation of the characteristics and uses of metals;
Introduction to the ways of improving metals;
Discussion on the environmental problems arose from abandoned metals.
Content Outline
This programme is divisible into 5 parts as follows:
(1) History of using metals
- History of men using metals can be roughly divided into several stages;
including mainly the era of using gold, silver, copper and iron. The easier the
metal can be extracted, the earlier it will be used by men.
- Gold is mainly distributed in gravels in riverbeds. As it does not combine
with other substances, it is discovered at an earlier stage. Gold is treated as a
rare metal and is usually used to manufacture decorative items.
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Apart from a small amount that exists independently, silver is usually found
in ores which also contains lead. Silver is also a rare metal and is always used
in minting coins in history.
Copperwares are mainly made from bronze apart from pure copper. As
bronze is harder than pure copper, it is more suitable for manufacturing
utensils.
Iron content on earth is comparatively higher than that of the other metals. As
it is also harder than other metals, it is widely adopted for use. Iron wares are
normally made from steel containing iron, instead of from pure iron.
(2) Extraction of metals
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The main components in metal ores are oxides, sulphides, halides, carbonates
and sulphates.
The programme shows the experiment of heating lead oxide with charcoal to
obtain lead.
(3) Properties and uses of metals
- Uses of metals are closely related to their properties. The programme
introduces the properties and uses of metals like aluminum, copper, gold,
silver, lead, magnesium and titanium.
- The programme points out the fact that metals are usually glossy and good
conductor of heat and electricity. Different metals have different malleability.
As some metals are more malleable than others, they can be used to make
products bearing different shapes.
(4) Improvement of metals
- To improve the nature of natural metals, the main way is by making alloys.
When a kind of metal combines with another kind of metal or non-metal
element in a special way, alloy will be formed.
- The programme introduces alloys like bronze (copper and tin), brass (copper
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and zinc), welding materials (lead and tin) and steel.
The programme introduces “shape-memory alloy” and points out that these
alloys can ‘memorize’ two different shapes. Such intelligence arises from the
fact that these alloys have two different phases while in solid states; just like
water, which can exist in gas, liquid and solid phase. It means that these
alloys exist in a certain form at a certain temperature while at another
temperature, they will change to another form. This is caused by the fact that
the arrangement of particles in these alloys differs at different temperatures,
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so that they can appear differently at different temperatures.
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The programme shows the following experiment; stretching a shape-memory
alloy wire at room temperature to change its shape. Then place it in hot water
or under hot air to increase its temperature, the wire resumes its original
shape. The programme also introduces the uses of such shape-memory
alloys.
The programme introduces super-conductors and points out that they are
materials bearing extra high capability of conducting electricity and can
therefore be used for hi-tech products such as magnetic levitation trains and
medical appliances like magnetic resonance imaging equipments.
Space alloys refers to the alloys made by using space technology. As it is
easier to obtain a super vacuum and zero-gravity state in space than on earth,
it would enable a more suitable environment for homogeneously mixing two
or more metals with different densities and create completely perfect alloy
crystals to cater for special needs.
(5) Recycling of metals
- As the metal resources on earth are limited, some metal wastes will be
collected and sent to factories for processing to be recycled into raw
materials or to be re-used.
Suggestions for Utilization
The teacher can screen the programme in whole or in parts according to actual needs.
The teacher may spend 5 to 10 minutes at the beginning of each lesson to lead
students to discuss with reference to the Preparation before viewing the programme
part of the Suggested Activities. The teacher may then show the programme. After
the show, the teacher may spend another 10 to 15 minutes to discuss with students
with a view to consolidating the concepts and methods illustrated in the programme.
The teacher is advised to refer to the Activities after viewing the programme part of
Suggested Activities.
Suggested Activities
(The following activities are suggested for teacher’s reference only. The teacher may
wish to use the activities according to students’ abilities, the learning environment of
the class, and the teaching time available.)
Preparation before viewing the programme
 Let students take a look at some metal specimens and ask them to name some of
their properties and uses.
 Engage students in discussion on re-cycling and re-use of metals.
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Activities after viewing the programme
 Teachers can encourage students to undertake the following study :
- Research on the history of using metals;
- Collect some examples of metal wares from our daily use and find out the
properties of the relevant metals. Analyze the reasons behind using such
metals for making the products.
- Research on the situation about metal recycling and re-use in Hong Kong.
 Teachers can also let students conduct some simple experiments on metal
extracting, such as placing copper oxide or lead oxide on some carbon powder
and heat it to obtain copper and lead respectively.
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