Metal mixtures (alloys)
In this topic you will:
- learn about metal mixtures (alloys)
- use particle theory to explain the differences in the properties of metals and their alloys.
Key Words
alloy, bronze, disrupt, steel
Alloys
Metal mixtures are called alloys. Alloys are made by mixing different metals together and melting them. The atoms of the different metals mix but do not bond together. The properties of the alloys are different from the metals they contain.
Bronze is an alloy made by mixing copper and tin. Bronze is harder than either copper or tin.
Steel is an alloy, but an unusual one because one of the elements in the mixture is not a metal. Steel is a mixture of iron and carbon. Pure iron is not hard enough to be very useful but when it is mixed with other elements to form steel it is much harder.
Sometimes, chromium and nickel are also added to steel. This type of steel does not rust and is used for cutlery.
The reasons why the alloys have different properties from the pure metal is to do with the arrangement of the particles of the elements. In a pure metal, the atoms are all the same size and arranged in regular rows. The layers can slide over one another easily. This is what happens when the metal is hit with a hammer. What do we call this property? This also happens when the metal is stretched out. What do we call this property?
Quick Fact
Alloys often have improved properties compared to pure metals — like increased strength, resistance to rust, or improved hardness.
An alloy. The layers of atoms can’t slide over each other as easily now. They get stuck in place. This makes the alloy a lot harder and stronger than the original metal.
Important Concept
Alloys are harder than pure metals because different-sized atoms disrupt the layers, preventing them from sliding over each other easily.
Think Like a Scientist
Investigation: Modelling a Metal and an Alloy
In this activity, you'll use bubbles to model the arrangement of atoms in a metal and see how adding an atom of a different size affects the structure — like forming an alloy.
You will need: A Petri dish, diluted washing-up liquid, and a syringe
Steps:
- Fill the Petri dish with diluted washing-up liquid.
- Use the syringe to gently create rows of small bubbles. Push steadily to make them uniform in size. These bubbles represent atoms in a metal.
- Observe how the bubbles pack closely and form a regular pattern.
- Inject a slightly larger bubble in the middle of the dish by pressing harder or longer on the syringe. This simulates adding an atom of a different element to form an alloy.
- Watch what happens to the pattern around the larger bubble.
Now answer these questions:
- Do the bubbles line up in rows? What does this represent in a metal?
- What happens when a bubble bursts?
- Can the rows of bubbles slide past each other? Why is this important?
- How does the large bubble change the pattern? What does this model show about alloys?
Show Answer
1. Yes, the small bubbles line up in a regular pattern, representing atoms in a pure metal.
2. If a bubble bursts, the pattern is disrupted — similar to a defect in the structure.
3. In a pure metal, rows of atoms can slide past each other easily, which makes metals malleable.
4. The larger bubble disrupts the regular pattern, showing how an alloy resists movement — making it harder and stronger.
Alloys in everyday life
Coins
The coins in your pockets are made from alloys. Pure metals are too soft to withstand all the wear they get. The coins that look silver are not made of silver – it is too soft and far too expensive. The silver coins are made of alloys containing copper and nickel. The copper coins contain copper, zinc and tin. Coins must be hardwearing but also malleable enough to be stamped with complex patterns.
Jewellery
Most gold jewellery is not pure gold; it is an alloy of gold and copper. Pure gold is soft. If you used pure gold for something like a wedding ring (that gets a lot of wear and tear) it would wear away. A wedding ring should be made from something stronger. Pure gold is 24 carat: that means that 24 parts out of 24 are gold. 18 carat gold has 18 parts out of 24 of pure gold, and six parts of other metals such as copper, silver or zinc.
Aeroplanes
The metal used to build planes needs to be light but very strong. Planes are mainly made of aluminium, but pure aluminium would not be strong enough and the plane’s wings would fall off because of the great stress put on them during flight. By adding magnesium and copper, an alloy called duralumin is formed. Duralumin is about five times stronger than pure aluminium.
Common Mistake
Don’t assume that all coins and jewellery are made of pure metals — they’re often carefully designed alloys chosen for strength, cost, and durability.
Artificial joints
The joints in our bodies take a lot of wear and tear. Sometimes, the joints are attacked by arthritis. This is a very painful and crippling disease. Now people can be fitted with replacement joints. These are made of plastic and alloys, often alloys of titanium.
Modern alloys
Modern alloys have been developed that have some very useful properties. Some glasses frames are made of shape memory alloy. This alloy is called Nitinol. Nitinol is made of nickel and titanium.
Example
Shape memory alloys like Nitinol can return to their original shape after being bent. This makes them ideal for products like flexible eyeglass frames and medical stents.
Questions
Show Answer
A mixture of metals.
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It is light.
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Pure aluminium is weak.
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It means 24 parts out of 24 are gold — pure gold.
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18 carat gold is less pure than 24 carat gold.
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It is weak.
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Because it is cheap.
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It must be strong and biocompatible.
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Because it returns to its original shape after bending.
Brass and bronze
Brass is an alloy of copper and zinc. There are different types of brass, made by using different amounts of copper and zinc. Sometimes, other elements such as lead, aluminium, manganese or silicon are added.
Look at the table of information about copper, zinc and brass.
| Name | Copper | Zinc | Brass |
|---|---|---|---|
 |
 |
 |
|
| Element or mixture? | element | element | mixture |
| Appearance | reddish brown soft metal | silvery grey soft metal | golden yellow, reddish gold or silver soft alloy |
| Melting point | 1085°C | 419.5°C | 900–1000°C |
| Properties | very ductile and malleable | less ductile and malleable than copper | less ductile than copper; more malleable than zinc and copper |
| conducts heat and electricity well | conducts heat and electricity less well than copper | conducts heat and electricity less well than zinc | |
| resistant to corrosion | |||
| Example uses | electrical wiring; central heating pipes | to cover iron in a thin layer to prevent it from rusting | musical instruments, plumbing |
Quick Fact
Brass is not a pure substance — it is a mixture of two metals, copper and zinc, which gives it useful properties like corrosion resistance and variable strength depending on composition.
Look at the melting points: copper and zinc have just one temperature listed. However, brass has a range of temperatures. There are many different types of brass, which are made by using different amounts of copper and zinc. So, there is no specific melting point for brass; it depends on the proportions of copper and zinc that have been used.
Another alloy of copper is bronze. Bronze is an alloy that is made by mixing copper with tin. Sometimes, other elements such as manganese, phosphorous, aluminium or silicon are added. Mixing different amounts of copper and tin makes the different forms of bronze. Each different mixture has its own different melting point.
| Name | Copper | Tin | Bronze |
|---|---|---|---|
 |
 |
 |
|
| Element or mixture? | element | element | mixture |
| Appearance | reddish brown soft metal | white metal | reddish brown not as bright as brass |
| Melting point | 1085°C | 232°C | 860–1150°C |
| Properties | very ductile and malleable | soft, ductile and malleable | less ductile than copper; hard; brittle |
| conducts heat and electricity well | conducts electricity less well than copper | good conductor of electricity | |
| does not corrode readily | corrosion resistant | ||
| Example uses | electrical wiring; central heating pipes | coating the inside of food cans and in many different alloys | bronze sculptures; bells and cymbals; ship fittings (especially parts submerged under water); electrical connectors |
Important Concept
Bronze is an alloy made by combining copper and tin. Its hardness and resistance to corrosion make it ideal for sculptures, bells, and underwater applications.
Questions
Show Answer
Because bronze is an alloy and its melting point varies depending on the proportions of metals used.
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Both are less ductile than copper.
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They both conduct heat well (though copper does so better).
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Copper has a higher melting point than tin.