Metals 2

3 of 49 © Boardworks Ltd 2006
How many different uses of metal can you spot?
What are metals used for?

Why are metals important?
Metals are a highly valuable group of materials, used for
hundreds of products and produced in huge quantities.
 35,500,000 tons of
aluminium were
produced in 2005.
 The production of copper
increased by more than
20 times in the 20th century.
 Gold is worth more than
£10,000 per kilogram.
Metals have played a vital role in human development.
Periods of civilization are even classified by the metals
that were used during those times, such as the Iron Age.

Uses of metals – activity

What else can metals be used for?
It is easy to find products made from metals, but there are
other uses of metals that are less obvious.
Compounds containing metals have many
uses. For example, metal compounds are
used to colour materials including stained
glass and even make-up!
Metals are used as catalysts to
speed up reactions. Nickel is used
as a catalyst to make margarine.
Platinum is used in catalytic
converters in car exhausts to clean
up fumes and reduce pollution.
Can you find any other uses of metals?

What decides what metals are used for?
It is not only the properties of a metal that determines its use.
What other factors might determine how metals are used?
For example, aluminium only became a
commonly used metal in the late 19th century
as better extraction methods made it cheaper.
For example, silver is a better conductor than copper
but it is too expensive to be used for electric wires.
 Cost. A metal may have the best properties
for a job but it might be too expensive.
 Extraction method. This can greatly affect
the price and availability of a metal.

What are the properties of different metals?
Do all metals behave in the same way?

What are the general properties of most metals?
 solid at room temperature
Why do metals have these particular properties?
Typical properties of metals
 high melting point
 good conductors of electricity and heat
 malleable: they can be shaped
 ductile: they can be drawn into wires
 strong
 dense

What is the structure of metals?
sea of electrons
metal ions
The atoms in a pure metal are in
tightly-packed layers, which form
a regular lattice structure.
The outer electrons of the metal
atoms separate from the atoms
and create a ‘sea of electrons’.
These electrons are delocalized
and so are free to move through
the whole structure.
The metal atoms become positively
charged ions and are attracted to
the sea of electrons. This attraction
is called metallic bonding.

Electrons and metallic bonding
How does the sea of electrons affect the properties of metals?

Why do metals have high melting points?
Metals often have high melting
points and boiling points. Gold,
for example, has a melting
point of 1064 °C and a boiling
point of 2807 °C.
The properties of metals are related to their structure.
In metal extraction and other industrial processes, furnaces
often run continuously to maintain the high temperatures
needed to work with molten metals.
This property is due to the
strong attraction between the
positively-charged metal ions
and the sea of electrons.

How do metals conduct heat and electricity?
Delocalized electrons in metallic bonding allow metals to
conduct heat and electricity.
This makes heat transfer in
metals very efficient.
Delocalized electrons also
conduct electricity through
metals in a similar way.
For example, when a metal is
heated, the delocalized electrons
gain kinetic energy.
These electrons then move faster
and so transfer the gained energy
throughout the metal.
heat

Metals are usually strong, not brittle. When a metal is hit,
the layers of metal ions are able to slide over each other,
and so the structure does not shatter.
Why are metals strong?
The metallic bonds do not break because the delocalized
electrons are free to move throughout the structure.
metal after it is hit
forceforce
This also explains why metals are malleable (easy to shape)
and ductile (can be drawn into wires).
metal before it is hit

Metallic bonding

Corrosion is the gradual destruction of a metal due to
reactions with other chemicals in its environment.
Over time, corrosion
changes the appearance of
the metal as it breaks down
and it becomes weaker.
What is corrosion?
Coating the surface of a metal
with paint and certain chemicals
can protect it from corrosion.
What happens if the protective coating becomes damaged?
Corrosion can seriously damage
metallic objects and structures.

Metals behave differently when exposed to the environment.
Items made from gold can
survive for thousands of
years and have even been
found in good condition
underwater.
Do all metals corrode?
In many cultures, gold is
considered a precious metal
and is used to make sacred
and decorative objects.
Gold is an unreactive metal and does not corrode easily.
In general, objects made from metals that corrode easily
do not survive for as long.

coating of
oxygen atoms
The outer aluminium atoms react with oxygen in the
atmosphere. This forms a thin layer of aluminium oxide on
the metal’s surface, which protects the metal from corrosion.
Aluminium is a very reactive metal. However, it does
not corrode in the presence of oxygen. Why is this?
oxygen in the
atmosphere
aluminium
atoms
Why doesn’t aluminium corrode?

Salt can increase the rate of rusting. This iron bolt is on a
seaside structure and is nearly completely corroded.
Rusting is the specific name
given to the corrosion of iron.
It is a chemical reaction between
iron, oxygen and water.
What is the word equation for the formation of rust?
What is rusting?
The chemical name for rust is
hydrated iron oxide. Rust can
form on cars and buildings,
making them unsafe. It is an
expensive problem.
hydrated iron oxidewater+ +iron oxygen

Rate of corrosion experiment

Are some metals easier to find than others?
Finding metals

Most metals are actually found combined with other elements,
as compounds in ores. These metals must be extracted
from their ores before they can be made useful.
Metals can be found in the Earth’s
crust combined with other elements or
uncombined as pure substances.
Where do metals come from?
Metals that are found in a pure form
are said to occur ‘native’.
Highly reactive metals, such as titanium, require complicated
extraction. This can increase the cost of the pure metal.
Some unreactive metals, like
gold, silver and copper, can be
found uncombined as elements.

potassium
sodium
calcium
magnesium
aluminium
zinc
iron
copper
gold
increasingreactivity
Metals above carbon in the
reactivity series must be
extracted using electrolysis.
Electrolysis can also be
used to purify copper.
Metals below carbon can
be extracted from their ores
by reduction using carbon,
coke or charcoal.
Platinum, gold, silver and
copper can occur native and
do not need to be extracted.
lead
silver
How does reactivity affect extraction?
The reactivity of a metal determines how it is extracted.
(carbon)
(hydrogen)
platinum

Metals that are less reactive
than carbon can be extracted
from their ores by burning with
carbon.
Iron is extracted by this method
in a blast furnace. The iron ore
is heated with carbon-rich coke
at very high temperatures.
The iron collected from a blast
furnace is only 96% pure.
How is carbon used to extract metals?
molten
iron
hot air
molten
slag
raw materials
Usually, this product will be
treated further because the
impurities make iron brittle.

Metals that are more reactive than carbon are extracted
using electrolysis.
This process uses an electrical current to extract the metal.
Electrolysis is more expensive than using a blast furnace,
and this increases the price of the metal.
What is electrolysis?
Electrolysis is also used to
further purify metals, such
as copper, after extraction
with carbon.
Aluminium is extracted
from its ore, bauxite,
using this method.

Extraction quiz

Metals are easy to recycle and do not change their properties.
What are the benefits of recycling metals?
Saves energy
Recycling aluminium uses 95% less
energy than extracting it from its ores.
Uses fewer
resources
Reduces
waste
Less damage
to environment
Profitable
Recycling reduces the need to mine
sensitive areas for new ores.
Recycling one car saves over 1,000kg of
iron ore and over 600kg of coal.
14 million fewer dustbins would be filled
per year by recycling aluminium in the UK.
Recycled copper can be resold for up to
90% of what it was worth when new.
Can metals be recycled?

What are the drawbacks of recycling?
Recycled copper is too impure for
electric wires. However, scrap
copper can be used in products
that do not need pure metal, such
as coins and ornaments.
Metallic materials are often mixtures of different metals.
Pure metals can be obtained by purifying recycled materials
but this can be expensive and may use more electricity than
extracting metals from ores.
Sorting mixed metals for recycling
can be difficult. Iron and steel (a
mixture of iron and other elements)
are exceptions. These materials
can be separated from waste
using a magnet.

An alloy is a mixture of a metal with at least one other
element.
The final alloy may have
very different properties
to the original metal.
By changing the amount
of each element in an
alloy, material scientists
can custom-make alloys
to fit a given job.
What is an alloy?
Steel is a common example of an alloy. It contains iron mixed
with carbon and other elements. Adding other elements to a
metal changes its structure and so changes its properties.

What types of alloys are there?
Alloys have been used for thousands of years. Bronze, an
alloy of copper and tin, was commonly used by civilizations
before iron extraction methods were developed.
 brass: an alloy of copper and zinc.
It does not tarnish and is used for door
knobs, buttons and musical instruments.
 solder: an alloy of zinc and lead. It
is used in electronics to attach
components to circuit boards.
 amalgam: an alloy of mercury and
silver or tin. It is used for dental fillings
because it can be shaped when warm
and resists corrosion.
Other well-known alloys include:

Although pure gold is sometimes used in electronics, gold
jewellery is always a mixture of gold and other metals.
Pure gold is actually quite soft. Adding small amounts of
other metals makes the gold hard enough to use in jewellery.
Alloying gold with different metals also affects its colour.
The familiar yellow gold is an
alloy of gold with copper and
silver. Adding more copper than
silver gives redder shades.
White gold is an alloy of gold
with nickel, platinum or palladium.
Around 12% of people may be
allergic to the nickel in white gold.
Is gold an alloy?

When is a copper coin not a copper coin?
When it is a copper-coated alloy!
Since 1992, UK copper coins have been made from
copper-plated steel and are magnetic. A magnet can be
used to separate copper coins by age.
Copper coins used to be made from
pure copper but most ‘copper’ coins
used around the world are now made
from copper alloys.
Previously, as the value of copper
increased, the metal used to make
the coin became worth more than the
actual coins. A melted-down, pure
copper coin could have been sold for
more than the face value of the coin!

Steel is an alloy of iron and other elements, including carbon,
nickel and chromium.
Steel is stronger than pure iron and can be used for
everything from sauce pans… …to suspension bridges!
What is steel?

The atoms of other elements
are different sizes. When other
elements are added to iron,
their atoms distort the regular
structure of the iron atoms.
The atoms in pure iron are
arranged in densely-packed
layers. These layers can slide
over each other. This makes
pure iron a very soft material.
Why is steel stronger than iron?
It is more difficult for the layers
of iron atoms in steel to slide
over each other and so this
alloy is stronger than pure iron.

Steel can contain up to 2% carbon.
 low carbon steel contains less than 0.25% carbon
 high carbon steel contains more than 0.5% carbon.
Two other important types of steel are:
What types of steel are there?
 stainless steel – an alloy of iron that contains at least
11% chromium and smaller amounts of nickel and carbon
 titanium steel – an alloy of iron and titanium.
Varying the amount of carbon gives
steel different properties. For
example, a higher carbon content
makes a hard steel.
Different types of steel are classified
by how much carbon they contain.

Using different types of steel

What’s so clever about smart alloys?
Shape memory alloy is a type of smart material made from
metals that returns to its original shape after being deformed.
A smart material can change one or more of its physical
characteristics under the influence of an external stimulus.
Nitinol is a type of shape
memory alloy made from
nickel and titanium.
Nitinol has also been used to hold badly broken bones
in place while they heal.
This material can be
used to make a pair of
glasses that ‘remembers’
its shape and does not
break when crushed.

Glossary (1/2)
 alloy – A mixture of a metal and at least one other element.
 amalgam – An alloy of mercury that is used for dental
fillings.
 blast furnace – A tall oven used to extract iron from iron
ore by burning it with carbon at high temperatures.
 brass – An alloy of copper and zinc that is used for
ornaments.
 corrosion – The destruction of a metal caused by
reactions with chemicals in the environment.
 ductile – The ability of metals to be drawn into wires.
 electrolysis – A process that uses electricity to extract or
purify metals.

Glossary (2/2)
 malleable – The ability of metals to be bent or hammered
into different shapes.
 native – The natural occurrence of a metal as an element
in the environment.
 ore – A rock that contains a metal combined with other
elements in concentrations that make it profitable to mine.
 rusting – The specific name for the corrosion of iron and
iron-containing alloys, such as steel.
 shape memory alloy – A type of alloy that can return to
its original shape after being deformed.
 solder – An alloy of lead and tin that is used in electronics.
 steel – An alloy containing iron and other elements.

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Metals 2

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