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.