Composition of Alloys

  • Alloys are mixtures of metals where the metals are not chemically combined.
  • They can also be made from metals mixed with non-metals such as carbon.
  • Alloys often have properties that can be very different from the metals they contain, for example they can have more strength, hardness or resistance to corrosion or extreme temperatures.
  • Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms.
  • This makes it more difficult for the layers to slide over each other, so they are usually much harder and stronger than the pure metal.

Structure of alloy, IGCSE & GCSE Chemistry revision notes

The regular arrangement of a metal lattice structure is distorted in alloys

Properties & Uses

  • Most of the metals that are in everyday use around us are alloys.
  • Some common examples are discussed below.

Copper Alloys

  • Bronze is an alloy made of copper and tin. It is harder than copper and is used to make ornaments and medals.
  • Brass is a common example of an alloy which contains 70% copper and 30% zinc. It is decorative and corrosion resistant and is used for low friction ornamental purposes such as plumbing and carpentry fittings.

Brass, IGCSE & GCSE Chemistry revision notes

Brass is used extensively in modern kitchen and bathroom fittings

Aluminium Alloys

  • Aluminium is mixed with copper, manganese and silicon for aircraft body production as aluminium alloys tend to be stronger and lighter than pure aluminium.
  • Aluminium and magnesium (5%) make an interesting alloy called magnalium which is also used extensively in automobile and aircraft construction.
  • As well as being lighter and stronger, it is also more corrosion resistant than aluminium.
  • Magnalium with 50% magnesium is used in the production of fireworks as it is more stable than pure magnesium but still burns brightly.

Gold Alloys

  • Gold alloys are used to make jewellery.
  • Gold metal is relatively soft and malleable so other metals such as copper, zinc and silver are added to provide strength and toughness.
  • Carats are used to express the purity of gold jewellery.
  • Pure gold with nothing else added is said to be 24 carat.
  • A 12 carat piece of gold jewellery therefore contains 50% gold.
  • For example a 12 carat necklace that weighs 50g contains 50% gold, so 25 grams.

Coloured-gold-rings, IGCSE & GCSE Chemistry revision notes

Rose, yellow and white gold are alloys of gold with varying proportions of Cu, Pd and Ag

Steel Alloys

  • Molten iron is an alloy of 96% iron, with carbon, phosphorus, silicon and sulfur impurities.
  • It is too brittle so most of it is converted into steel by removing some of the impurities.
  • Not all of the carbon is removed as steel contains some carbon, the percentage of which depends on the use of the steel.
  • Alloys of steel are made from adding other metals to steel such as chromium, manganese or nickel.
  • By carefully controlling the amounts added, the particular type of alloy required can be produced.
  • Steel alloys are used in construction, transport, manufacturing and other industries.

Steel Alloys Table, IGCSE & GCSE Chemistry revision notes
Drill, IGCSE & GCSE Chemistry revision notes

Diagram of a high carbon steel drill bit which are used for drilling through other metals

AQA GCSE Chemistry Notes

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Morgan Curtin Chemistry

Author: Morgan

Morgan’s passion for the Periodic Table begun on his 10th birthday when he received his first Chemistry set. After studying the subject at university he went on to become a fully fledged Chemistry teacher, and now works in an international school in Madrid! In his spare time he helps create our fantastic resources to help you ace your exams.