2.5.4Atoms, Elements and Compounds
Alloys — Cambridge IGCSE Chemistry 0620 Revision Notes & Topical Questions
5 min read 4 parts Lesson 13 of 26 Unit quiz
Part 1 of 4What an Alloy Is
An alloy is made by mixing a metal with other elements, so its properties can be better than those of the pure metal.
Definition
- Definition An alloy is a mixture of two or more metals, or a metal with a non-metal such as carbon, in a fixed proportion.
Steel
- Steel Steel is an alloy of iron with a small amount of carbon, and the amount of carbon controls how hard and brittle it is.
Brass
- Brass Brass is an alloy of copper and zinc, typically containing around 70% copper and 30% zinc.
Enhanced properties
- Enhanced properties Alloys are often stronger, harder and more resistant to corrosion or extreme temperatures than the pure metals they contain.
Part 2 of 4Why Alloys Are Harder
The structure of a pure metal allows its layers to slide, and alloying prevents this.
1
In a pure metal the atoms are arranged in regular layers that can slide over one another when a force is applied.
2
An alloy contains atoms of different sizes, which distort the regular arrangement of the metal lattice.
3
The distorted layers cannot slide easily past one another because the atoms do not fit neatly into the gaps.
4
This makes the alloy harder and stronger, so it is more useful for structures and tools than the pure metal.
Part 3 of 4Examples and Uses
Examples and Uses
Mild steel
- Mild steel Low carbon content makes it soft and malleable, so it suits car body panels and wires.
High-carbon steel
- High-carbon steel A higher carbon content makes steel hard, so it is used for tools such as chisels.
Stainless steel
- Stainless steel Chromium and nickel make it strong and resistant to corrosion, so it suits cutlery and chemical plants.
Brass
- Brass Its mix of copper and zinc gives a hard metal that is useful for fittings and decorative objects.
Part 4 of 4Exam Checklist & Tips
2.5.4 – Key Points for the Exam
- Alloy A mixture of a metal with other elements, usually other metals or carbon, designed to improve properties.
- Lattice The regular, repeating arrangement of atoms or ions in a solid metal.
- Distorted layers Layers of atoms in an alloy that are disrupted by atoms of different sizes.
- Malleable Able to be bent or shaped without breaking.
Common Mistakes
- Saying an alloy is a compound;
- alloys are mixtures, so the elements are not chemically bonded in fixed proportions.
- Stating that the atoms in an alloy are all the same size; the difference in size is what makes alloys harder.
- Describing alloys as weaker than pure metals;
- the intended purpose of alloying is to improve strength and hardness.
- Identifying a particle diagram as an alloy when the particles are all identical and in regular rows.
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