Alloys (CIE IGCSE Chemistry: Co-ordinated Sciences (Double Award))

• An alloy is a mixture of a metal with other elements
  • Most alloys contain more than one metal 
  • Some alloys contain non-metals

Properties and uses of alloys

• Two examples of alloys are:
  • Brass - an alloy of copper and zinc and is much stronger than either metal
    • It is used in musical instruments, ornaments and door knobs
  • Stainless steel - an alloy of iron and other elements, for example, chromium, nickel and carbon
    • It is used in cutlery because of its hardness and resistance to corrosion / rusting 
• Other alloys include:
  • Iron with tungsten - extremely hard and resistant to high temperatures
  • Iron with chromium / nickel - resistant to corrosion
  • Aluminium with copper, manganese and silicon - the alloy is stronger but still has a low density, which makes it ideal for aircraft body production

• Alloys often have properties that are different to the metals they contain
  • For example, they can be:
    • Stronger
    • Harder
    • Resistant to corrosion / extreme temperatures
  • These enhanced properties can make alloys more useful than pure metals

The structure of an alloy

• Alloys have a different structure to metals
  • Metals have a regular arrangement of ions 
  • Alloys have an irregular arrangement of atoms 

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

Extended tier only

• Alloys typically contain atoms of different sizes
• This distorts the normally regular arrangements of atoms in metals
  • The regular arrangement in a metal is layers of positive ions in a sea of delocalised electrons
• The distortion makes it more difficult for the layers to slide over each other
• So, alloys are usually harder / stronger than pure metals