S.4CHEM/METAL
P.1
Uses of Common Metals
I. Introduction
When we choose a metal for a particular purpose, we should consider its properties and
price.
Properties of the metals are about its :
--strength
--mass
--appearance
--malleability and ductility
--electrical and thermal conductivity
--ability to resist corrosion.
See P.123 Table 8.1 for Properties of some commonly used metals
Price of a metal is affected by its :
--abundance in the Earth
--cost of mining metal
--cost of extraction of metal.
Do P.124 Classwork
II. Relating uses of metals to their properties and prices
The following table shows the uses of different metals and the reasons.
Metal
Uses
Reasons for use
Aluminium windows frames
-resists corrosion
-strong -attractive
overhead power cables
-good electrical conductor
-low density -ductile
-cheaper than copper
aircraft body
-low density -light but strong
-resists corrosion
soft drink cans
-resists corrosion -low density
-non-poisonous -malleable
saucpans, cooking foil
-good thermal conductor -malleable
-non-poisonous -resists corrosion
Copper
electrical wires
-ductile -good electrical conductor
water pipes, tanks
-resists corrosion -non-poisonous
-malleable , ductile
-easy to weld by soldering
cooking utensils(煮食用具)
-good thermal conductor -non-poisonous
-resists corrosion -malleable
Iron
Bridge, gatings
-strong -hard -malleable -ductile
Titanium
space vehicles
-light but strong -resists corrosion
-withstands intense cold and heat without
loss of strength
Gold
jewellery
-shiny golden yellow colour
-precious -malleable -ductile
- resists corrosion
Lead
roofing
-soft -easy to shape
Silver
jewellery
-attractive silvery colour
-malleable -ductile -resists corrosion
Tin
coating 'tin cans'
-non-poisonous -unreactive
-malleable
Zinc
protecting iron by galvanizing resists corrosion because zinc is higher than
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S.4CHEM/METAL
P.2
iron in reactivity series.
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S.4CHEM/METAL
P.3
Question : Aluminium is resistant to weather corrosion. It is a good conductor of heat and
electricity and it has a low density. Give four uses of aluminium which best illustrate each of
these properties.
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Question : In the past, copper was used to make overhead cables.
i) Why was copper used ?
ii) What metal is used nowadays? Give reasons for the change
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Question : Iron can corrode easily. Why is it widely used as construction material?
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Do P.126 Decision making exercise
III.
Structure of Metals
In metals, the atoms are closely and regularly packed together. A giant lattice, or a
giant metallic structure is formed.
IV.
Metallic Bonding
-- Outer-shell electrons in metals are weakly attracted by the nucleus. These delocalised
electrons (sea of electrons)can move freely throughout the metal.
-- The strong electrostatic attraction between free electrons and positively charged metal
ions is metallic bond.
-- Metallic bonding is non-directional and found in metal only.
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S.4CHEM/METAL
P.4
V. Physical properties of common metals
i) Hard and dense
--It is because the atoms are closely packed in the crystal lattice.
ii) High melting and boiling points
-- Metals forms a giant lattice and metallic bonds are usually strong. To separate the
atoms, much energy is needed to break the bond.
-- The strength of metallic bond depends on the number of outer-shell electrons.
Metals with greater number of outer-shell electrons have higher melting points.
iii) Malleable and ductile
--Metals consist of layers of atoms.When a force is applied, the layers can slip over one
another.
--The metal does not break as the non-directional metallic bonds still hold the atoms
together.
iv) Good conductor of heat
--The mobile (free ) electrons can conduct heat.
--The electrons move faster and hit other electrons when heated.
v) Good conductor of electricity
--Metal conduct electricity by the movement of free electrons
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