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2.5.4Inorganic Chemistry

Alloys — Edexcel Linear - OL (Chemistry) Revision Notes & Topical Questions

5 min read 5 parts Lesson 19 of 23 Unit quiz

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Part 1 of 5What Is an Alloy?

2.5.4 Alloys

Pure metals are often too soft for many uses, so they are combined with other elements.

Definition
  • An alloy is a mixture of a metal with one or more other elements, which may be metals or non-metals such as carbon.
Steel
  • Steel is an alloy of iron with a small amount of carbon.
Brass
  • Brass is an alloy of about 70% copper and 30% zinc.
Why make alloys
  • Alloying changes the properties, often producing a material that is harder, stronger or more resistant to corrosion.

Part 2 of 5Structure of Pure Metals and Alloys

Structure of Pure Metals and Alloys
Pure metal
  • The atoms are all the same size and are arranged in regular layers.
Sliding layers
  • Because the layers are regular, they slide over each other easily when a force is applied, so a pure metal is soft and malleable.
Alloy
  • The added atoms are a different size, which distorts the regular layers.
Harder material
  • The distorted layers cannot slide easily, so a larger force is needed to change the shape, making the alloy harder.
FeaturePure metalAlloy
Atom sizesAll the sameDifferent sizes
LayersRegularDistorted
HardnessSofterHarder

Part 3 of 5Examples of Steels

Examples of Steels
Mild steel
  • Mild steel has a low carbon content and stays soft and malleable, so it is used for car panels.
High carbon steel
  • A higher carbon content makes it hard but more brittle, suited to tools like chisels.
Stainless steel
  • Adding chromium and nickel gives a strong steel that resists corrosion, used for cutlery and sinks.
Comparison with iron
  • Pure iron is too soft for most uses, so steels are used instead.

Part 4 of 5Answering Exam Questions on Alloys

1
Draw or describe the regular layers of identical atoms in the pure metal.
2
State that the alloy contains atoms of different sizes.
3
Explain that the different atoms disrupt the regular arrangement of layers.
4
Conclude that the layers cannot slide as easily, so the alloy is harder than the pure metal.

Part 5 of 5Exam Checklist & Tips

2.5.4 – Key Points for the Exam

  • Alloy A mixture of a metal with at least one other element.
  • Lattice A regular three-dimensional arrangement of particles.
  • Steel An alloy of iron and carbon.
  • Brass An alloy of copper and zinc.

Common Mistakes

  • Calling an alloy a compound; it is a mixture and the elements are not chemically bonded in fixed ratios.
  • Saying alloys are harder because the atoms are stronger rather than because the layers cannot slide.
  • Drawing alloy particles all the same size.
  • Forgetting that an alloy can contain a non-metal such as carbon.

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