AQA GCSE Combined Science (8464), Higher tier · Chemistry › Bonding, structure, and the properties of matter › How bonding and structure are related to the properties of
Practise Properties of metals and alloys. 14 exam-style questions on this subtopic, at up to four difficulty levels, with full mark schemes and a progress tracker. Free, no account needed.
Why most metals have high melting points and can be bent and shaped, and why alloys are harder than pure metals. Expect 2 to 4 mark 'explain' questions, often with diagrams of the layers of atoms in a pure metal and in an alloy.
Grade by grade
What you need to be able to do, from the first marks up to the top grade.
3
State that pure metals can be bent and shapedThe atoms in a pure metal are arranged in layers.
4
Define an alloyA mixture of a metal with other elements, usually other metals.
5
Explain why most metals have high melting pointsGiant structures with strong metallic bonding need a lot of energy to overcome.
5
Explain why pure metals are softThe layers of atoms can slide over each other easily.
6
Explain why alloys are harder than pure metalsAtoms of different sizes distort the layers, so the layers cannot slide over each other as easily.
7
Interpret diagrams of pure metals and alloysRegular layers of identical atoms compared with layers disrupted by atoms of a different size.
Notes
High melting points
Metals have giant structures with strong metallic bonding: strong electrostatic attraction between positive metal ions and delocalised electrons.
A lot of energy is needed to overcome this attraction, so most metals have high melting and boiling points.
Pure metals can be bent and shaped
In a pure metal, all the atoms are the same size and are arranged in regular layers.
When a force is applied, the layers can slide over each other, so the metal changes shape instead of breaking.
So pure metals can be bent and shaped, but many are too soft for many uses. For example, pure iron and pure gold are too soft for most tools and jewellery.
Alloys are harder
An alloy is a mixture of a metal with other elements, usually other metals. Examples: brass (copper and zinc), bronze (copper and tin), steel (iron with carbon and often other metals).
The atoms of the added elements are a different size from the atoms of the main metal.
These different-sized atoms distort the layers, so it is much harder for the layers to slide over each other.
So alloys are harder than pure metals, which makes them more useful for many purposes.
Cheatsheet
Metals: giant structures, strong metallic bonding → most have high melting points
Pure metal: same-sized atoms in layers that slide over each other → can be bent and shaped (soft)
Alloy = mixture of a metal with other elements (usually other metals)
Brass = copper + zinc; bronze = copper + tin; steel = iron + carbon (and often other metals)
How to answer each type of question
Explain why a pure metal can be bent and shaped
2 marks5
Say the atoms are arranged in layers.
Say the layers can slide over each other.
Example. Explain why gold can be hammered into thin sheets.
Show the model answer
Gold atoms are arranged in layers (1). The layers can slide over each other (1).
Explain why a metal has a high melting point
3 marks5
Name the structure: giant metallic structure.
Describe the bonding: strong electrostatic attraction between positive ions and delocalised electrons.
Say a lot of energy is needed to overcome it.
Example. Iron melts at 1538 °C. Explain why iron has a high melting point.
Show the model answer
Iron has a giant metallic structure (1). There is strong electrostatic attraction between the positive ions and the delocalised electrons (strong metallic bonds) (1). A lot of energy is needed to overcome this attraction (1).
Explain why an alloy is harder than a pure metal
3 marks6
Pure metal: atoms of the same size in regular layers that slide easily.
Alloy: atoms of a different size distort the layers.
So the layers cannot slide over each other as easily.
Example. Pure copper is too soft to make coins. Some coins are made from an alloy of copper and nickel. Explain why the alloy is harder than pure copper.
Show the model answer
In pure copper, all the atoms are the same size and are arranged in layers that can slide over each other (1). In the alloy, the nickel atoms are a different size from the copper atoms, so the layers are distorted (1). This makes it more difficult for the layers to slide over each other (1).
Different size is the key phrase in every alloy answer.
Picture a tray of identical marbles: the rows roll past each other easily. Add a few bigger marbles and the rows jam.
Where marks are lost
Saying alloys are harder because they have stronger bonds. The key idea is that different-sized atoms distort the layers so they can't slide.
Saying the layers in an alloy cannot slide at all. They slide less easily.
Saying pure metals bend because metallic bonds are weak. The bonds are strong; the layers slide.
Calling an alloy a compound. It is a mixture.
Forgetting to say that the atoms in the alloy are of different sizes.
Exam technique
Describe both structures: the pure metal (regular layers that slide) and the alloy (different-sized atoms, distorted layers).
If a diagram is given, refer to it, e.g. 'the larger atoms in the alloy disrupt the layers'.
Use the words 'layers' and 'slide': these are what mark schemes look for.
Quick recall
Cover the answers and test yourself. The app has these as flashcards that come back just before you'd forget them.
Metals and alloys are used for many purposes. What is an alloy?
A mixture of a metal with at least one other element (usually another metal).
Sample questions
Written for this site in the style of AQA exam questions. They are not taken from real past papers.
Question 1Easy5 marks
Metals and alloys are used for many purposes.
(a) Complete the sentence. Tick (✓) one box. In pure metals, the atoms are arranged in ................[1]
layers
pairs
a random mixture
small molecules
(b) What is an alloy?[1]
(c) Why are alloys used instead of pure metals for many purposes? Tick (✓) one box.[1]
Alloys are harder.
Alloys are softer.
Alloys are always cheaper.
Alloys conduct electricity better.
(d) Most metals have high melting points. Explain why.[2]
Show the answer and mark scheme
(a)Answer: layers
(b)Answer: A mixture of a metal with at least one other element (usually another metal).
a mixture of a metal with (at least) one other element / other metals
(c)Answer: Alloys are harder.
(d)Answer: Metals have giant structures with strong metallic bonding, which needs a lot of energy to overcome.
giant structure with strong metallic bonding / strong attraction between positive ions and delocalised electrons
a lot of energy is needed to overcome the metallic bonding
Question 2Medium8 marks
Duralumin is an alloy used to make aircraft. It contains 4.4% copper, 1.5% magnesium and 0.6% manganese by mass. The rest is aluminium.
(a) Calculate the percentage of aluminium in duralumin.[1]
(b) Calculate the mass of copper in 250 kg of duralumin.[2]
(c) Explain why duralumin is harder than pure aluminium.[3]
(d) Pure aluminium melts at 660 °C. Explain why aluminium has a high melting point.[2]
Show the answer and mark scheme
(a)Answer: 93.5%
(100 − 4.4 − 1.5 − 0.6 =) 93.5 (%)
(b)Answer: 11 kg
250 × 4.4 ÷ 100
11 (kg)
(c)Answer: The copper, magnesium and manganese atoms are different sizes from aluminium atoms; they distort the layers so the layers cannot slide easily.
atoms of copper / magnesium / manganese are a different size from aluminium atoms
(so) the layers of aluminium atoms are distorted
(so) the layers cannot slide over each other easily
(d)Answer: It has a giant structure with strong metallic bonding (attraction between positive ions and delocalised electrons), which needs a lot of energy to overcome.
strong electrostatic attraction between the positive ions and the delocalised electrons / strong metallic bonding (in a giant structure)
a lot of energy is needed to overcome it
Question 3Hard6 marks
Steel is an alloy of iron and carbon. Carbon atoms are much smaller than iron atoms. Relative atomic masses (Ar): C = 12, Fe = 56
(a) A student said: 'Alloys are harder than pure metals because the atoms that are added are bigger.' Use the information about steel to explain why the student is wrong.[2]
(b) A sample of steel contains 1.0% carbon by mass. Calculate the number of carbon atoms for every 100 iron atoms in this steel.[3]
(c) Suggest why a small percentage of carbon by mass has a large effect on the hardness of iron.[1]
Show the answer and mark scheme
(a)Answer: Carbon atoms are smaller than iron atoms, yet steel is harder than iron: atoms of any different size distort the layers so they cannot slide easily.
carbon atoms are smaller than iron atoms but steel is still harder than iron
atoms of a different size (larger or smaller) distort the layers so they cannot slide easily
(b)Answer: about 4.7
in 100 g: moles of C = 1.0 ÷ 12 = 0.0833 and moles of Fe = 99.0 ÷ 56 = 1.77
ratio C : Fe = 0.0833 ÷ 1.77 = 0.047
4.7 (carbon atoms per 100 iron atoms)
(c)Answer: Carbon atoms are light, so 1% by mass is about 5% of the atoms, and each carbon atom disrupts the layers around it.
carbon atoms are light so 1% by mass is a larger percentage of the atoms / each carbon atom distorts the layers around it