Metals
Metals are malleable - they can be bent and shaped without breaking. This is because
they consist of layers of atoms that can slide over one another when the metal is bent,
hammered or pressed.
Metallic bonds
Metals form giant structures in which electrons in the outer shells of the metal atoms
are free to move. The metallic bond is the force of attraction between these free
electrons and metal ions. Metallic bonds are strong, so metals can maintain a regular
structure and usually have high melting and boiling points.
Metals are good conductors of electricity and heat. This is because the delocalised
electrons can move throughout the metal.
Metal extraction and the reactivity series
The method used to extract a metal from its ore depends upon the stability of
its compound in the ore, which in turn depends upon the reactivity of the metal:


The oxides of very reactive metals, such as aluminium, form stable oxides and other
compounds. A lot of energy is needed to reduce them to extract the metal.
The oxides of less reactive metals, such as iron, form less stable oxides and other
compounds. Relatively little energy is needed to reduce them to extract the metal.
So, the method of extraction of a metal from its ore depends on the metal's position in
the reactivity series.
Reactivity and extraction method
The table displays some metals in decreasing order of reactivity and the methods used
to extract them.
Metal
Method
Potassium
Electrolysis
Sodium
Electrolysis
Calcium
Electrolysis
Magnesium
Electrolysis
Aluminium
Electrolysis
(Carbon)
(Non-metal)
Zinc
Reduction by carbon or carbon monoxide
Iron
Reduction by carbon or carbon monoxide
Tin
Reduction by carbon or carbon monoxide
Lead
Reduction by carbon or carbon monoxide
(Hydrogen)
(Non-metal)
Copper
Various chemical reactions
Silver
Various chemical reactions
Gold
Various chemical reactions
Platinum
Various chemical reactions
We can see from the table that reactive metals, such as aluminium, are extracted
by electrolysis, while a less reactive metal, such as iron, may be extracted by
reduction with carbon.
Because gold it is so unreactive, it is found as the native metal and not as a
compound. It does not need to be chemically separated .However, chemical reactions
may be needed to remove other elements that might contaminate the metal.
Extracting aluminium
Aluminium is the most abundant metal on Earth. But it is expensive, largely because
of the amount of electricity used in the extraction process.
Aluminium ore is called bauxite. The bauxite is purified to yield a white powder aluminium oxide - from which aluminium can be extracted.
The extraction is done by electrolysis. But first the aluminium oxide must be melted
so that electricity can pass through it. However, aluminium oxide has a very high
melting point (over 2000°C) so it would be expensive to melt it.
Instead, it is dissolved in molten cryolite - an aluminium compound with a lower
melting point than aluminium oxide. The use of molten cryolite as a solvent reduces
some of the energy costs involved in extracting aluminium.
The diagram shows an aluminium oxide electrolysis cell. Both the
negative electrode (cathode) and positive electrode (anode) are made of graphite, a
form of carbon.
Aluminium ions receive electrons at the negative electrode and are reduced to
aluminium atoms:
Al3+ + 3e- → Al
The molten aluminium sinks to the bottom of the cell, where it is tapped off.
Oxide ions lose electrons at the positive electrodes and are oxidised to oxygen gas:
2O2- → O2 + 4eThis oxygen reacts with the carbon of the positive electrodes, forming carbon dioxide,
so they gradually burn away. As a result, the positive electrodes have to be replaced
frequently. This adds to the cost of the process.
Extracting iron
The blast furnace
Iron is extracted from iron ore in a huge container called a blast furnace. Iron ores
such as haematite contain iron(III) oxide, Fe2O3. The oxygen must be removed from
the iron(III) oxide in order to leave the iron behind. Reactions in which oxygen is
removed are called reduction reactions.
Carbon is more reactive than iron, so it can displace iron from iron(III) oxide. Here
are the equations for the reaction:
Iron(III) oxide + carbon → iron + carbon dioxide
2Fe2O3(s) + 3C(s) → 4Fe(l) + 3CO2(g)
In this reaction, the iron(III) oxide is reduced to iron, and the carbon isoxidised to
carbon dioxide.
In the blast furnace, it is so hot that carbon monoxide can be used, in place of carbon,
to reduce the iron(III) oxide:
iron(III) oxide + carbon monoxide → iron + carbon dioxide
Fe2O3(s) + 3CO(s) → 2Fe(l) + 3CO2(g)
Raw materials for the reaction
Raw
material
Iron ore
(haematite)
Coke
Limestone
Air
Contains
Function
Iron(III)
oxide
A compound that contains iron
Carbon
Burns in air to produce heat, and
reacts to form carbon monoxide
(needed to reduce the iron oxide)
Calcium
carbonate
Helps to remove acidic impurities
from the iron by reacting with them
to form molten slag
Oxygen
Allows the coke to burn, and so
produces heat
Uses of iron and aluminium
Iron and steel
Iron is an element. Steel is an alloy of iron with carbon and sometimes other elements
in very small quantities. Steel is harder and stronger than iron and less likely to rust.
Iron versus aluminium in the car industry
Iron and aluminium are used to build cars. They are both malleable - they can be bent
or pressed into shape. The table summarises some differences in their properties.
Iron
Density
High
Aluminium
Low
Iron
Aluminium
Magnetic
Yes
No
Corrodes easily
Yes
No
Aluminium has some advantages over steel. Since it has a lower density than iron or
steel, a car body made from aluminium will be lighter than the same car body made
from steel. This results in improved fuel economy.
Also, aluminium does not corrode easily because it has a protective layer of
aluminium oxide. Therefore, a car body made from aluminium will corrode less than
one made from steel. It should last longer as a result.
However, aluminium is more expensive than steel. A car made from aluminium is
likely to be more expensive than one made from steel.
Other uses of iron and steel
Steel is widely used in the construction industry. For example:



it is used for the frames of many large buildings, and in the construction of bridges,
because it is very strong
it is used in cables for cranes because it is very strong under tension (when stretched)
it is used to reinforce concrete because it expands and contracts at the same rate when
heated and cooled, and it adds strength and flexibility to the concrete (which would be brittle
without it)
Other uses of aluminium
Aluminium has a variety of uses. For example:



it is used in the aerospace industry because of its low density
it is used in the home as foil for wrapping and storing food because its protective
oxide layer prevents it from reacting with the chemicals in food
it is used in high voltage power lines in the National Grid because it is a
good conductor of electricity, and its low density prevents the wires from sagging too much
or breaking under their own weight
Uses of iron and aluminium
Alloys
An alloy is a mixture of two or more elements, where at least one element is a metal.
Most alloys are mixtures of two or more metals.
For example, brass is a mixture of copper and zinc. Steel is an alloy of iron with
carbon, but other elements may also be added to change its properties.
Alloys are useful because the properties of the alloy are different from the properties
of the elements they are made from.
Layers
Alloys contain atoms of different sizes. These different sizes distort the regular
arrangements of atoms. This makes it more difficult for the layers to slide over each
other, so alloys are harder than the pure metal.
It is more difficult for layers of atoms to slide over each other in alloys
Copper, gold and aluminium are too soft for many uses. They are mixed with other
metals to make them harder for everyday use.
For example:



brass - used in electrical fittings - is 70% copper and 30% zinc
18-carat gold - used in jewellery - is 75% gold and 25% copper and other metals
duralumin - used in aircraft manufacture - is 96% aluminium and 4% copper and
other metals
Different steel alloys
Steel is mainly iron with some carbon in it. Changing the amount of carbon and other
trace elements changes the properties of the specific type of steel.
Contains
Mild
steel
Properties
Less than
1% carbon
(in addition Malleable,
to iron)
ductile
11%
Stainless chromium
(in addition Hard, does
steel
to iron)
not rust
Tool
steel
18%
tungsten (in
addition to
iron)
Hard,
resistant to
high
temperatures
Price
Uses
Car bodies
Relatively and
cheap
machinery
Cutlery,
Quite
surgical
expensive instruments
Quite
expensive Drill bits
Glossary
1.
2.
3.
4.
5.
6.
abundant If there is a lot of something, it is described as being
abundant.
Acidic Having a pH less than 7.
Alloy A compound of two or more elements, at least one of which
is a metal.
Atom All elements are made of atoms. An atom consists of a
nucleus containing protons and neutrons, surrounded by electrons.
Basic Bases react with acids to make salts, and form alkaline
solutions if they dissolve in water. Substances or solutions that act as
bases are said to be basic.
Compound A substance formed by the chemical union of two or
more elements.
7.
Conductor An electrical conductor is a material which allows an
electrical current to pass through it easily. It has a low resistance. A
thermal conductor allows thermal energy to be transferred through it
easily.
8.
Corrosion The destruction of a metal by oxidation or chemical
action, eg rusting.
9.
Decompose If a substance decomposes, it breaks down into
simpler compounds or elements.
10.
Delocalized Electrons that are not associated with a particular
atom/ion, eg in a metal, outer electrons can be free to move through the
solid.
11.
Density The ratio of mass to volume. It is usually measured in
grams per cubic centimetre or grams per cubic decimetre.
12.
Displace Take the place of another substance in a chemical
reaction. For example, a metal can displace a less reactive metal from its
oxide, removing oxide ions from the less reactive metal and becoming
an oxide itself.
13.
Dissolved When something is broken up in a liquid and no longer
exists.
14.
Electrode A conductor used to establish electrical contact with a
circuit. The electrode attached to the negative terminal of a battery is
called a negative electrode, or cathode. The electrode attached to the
positive terminal of a battery is the positive electrode, or anode.
15.
Electrolysis The decomposition (separation or break-down) of a
compound using an electric current.
16.
Electron Sub-atomic particle, with a negative charge and a
negligible mass relative to protons and neutrons.
17.
Element A substance made of one type of atom only.
18.
Ion Electrically charged particle, formed when an atom or
molecule gains or loses electrons.
19.
Molten Reduced to liquid form by heating. A term mainly used to
describe rock, glass or metal.
20.
Neutralization The reaction between an acid and a base to form a
salt plus water.
21.
Ore A rock containing enough quantities of a mineral that it would
be profitable to extract it.
22.
Oxidation The gain of oxygen, or loss of electrons, by a substance
during a chemical reaction.
23.
Cryolite. The name is derived from the Greek language words cryò = chill,
and lithòs = stone.
24.
Properties The characteristics of something. Chemical properties
include the reactions a substance can take part in. Physical properties
include colour and boiling point.
25.
Purified A substance that has been separated from other
substances is said to be purified.
26.
Reactive The tendency of a substance to undergo a chemical
reaction.
27.
Reactivity A measure of how vigorously a substance will react. The
more reactive it is, the greater its reactivity and the more vigorous its
reactions will be.
28.
Reduction A reaction in which oxygen is removed from a
substance. It also refers to a gain in electrons.
29.
Solvent The liquid in which the solute dissolves to form a solution.
30.
Thermally Using heat.
http://www.bbc.co.uk/education/guides/zfsk7ty/activity
Iron and aluminium
1
Which of these metal ores is the most stable?
Aluminium oxide
Lead oxide
Copper oxide
2
How is calcium metal extracted from the Earth's crust?
By electrolysis
By heating with carbon
It is found pure, so no need to extract it at all
3
How is platinum extracted from the Earth's crust?
By electrolysis
By heating with carbon
It is found pure, so no need to extract it at all
4
How is zinc extracted from the Earth's crust?
By electrolysis
By heating with carbon
It is found pure, so no need to extract it at all
5
Which is a typical property of metals?
Malleable
Brittle
Low melting point
6
How are metals bonded?
Positive and negative ions strongly attracted in a lattice
Atoms bonded by sharing electrons
Positive ions in a lattice with delocalised electrons in between
7
Why are metals good conductors of electricity?
The positive ions are free to move through the lattice
Electrons can move through the lattice
The metal ions are locked in place
8
What is the name of aluminium ore?
Haematite
Magnetite
Bauxite
9
What solvent is used to dissolve aluminium oxide in the extraction of aluminium?
Water
Ethanol
Cryolite
10
Why is limestone added to the blast furnace during the extraction of iron?
To reduce the iron oxide
To increase the temperature
To remove impurities in the iron ore
Check Score
Which of these metal ores is the most stable?
You said:
Aluminium oxide
Correct
Aluminium oxide is very stable because aluminium is a very reactive
metal.
2
How is calcium metal extracted from the Earth's crust?
You said:
By electrolysis
Correct
Calcium is above carbon in the reactivity series, so it must be extracted
using electrolysis.
3
How is platinum extracted from the Earth's crust?
You said:
It is found pure, so no need to extract it at all
Correct
Platinum is amongst the least reactive metals, so it is found pure in the
crust.
4
How is zinc extracted from the Earth's crust?
You said:
By heating with carbon
Correct
Zinc is below carbon in the reactivity series so it can be displaced from
its oxide ores by heating with carbon.
5
Which is a typical property of metals?
You said:
Malleable
Correct
Almost all metals are malleable, which means they can be beaten into
shape.
6
How are metals bonded?
You said:
Positive ions in a lattice with delocalised electrons in between
Correct
Metallic bonding occurs when positive metal ions are glued together by
delocalised electrons.
7
Why are metals good conductors of electricity?
You said:
Electrons can move through the lattice
Correct
The delocalised electrons are free to move in metals and these can carry
the charge.
8
What is the name of aluminium ore?
You said:
Bauxite
Correct
Bauxite is a reddish brown rock that contains aluminium oxide and
impurities.
9
What solvent is used to dissolve aluminium oxide in the extraction of
aluminium?
You said:
Cryolite
Correct
Cryolite is a compound made from sodium, aluminium and fluorine. It
dissolves aluminium oxide and allows electrolysis to take place.
10
Why is limestone added to the blast furnace during the extraction of
iron?
You said:
To remove impurities in the iron ore
Correct
Limestone is added to remove impurities in the iron ore. This forms slag
which can be easily removed.