Properties of Alloys (DP IB Chemistry): Revision Note

Alloys

What is an alloy?

• An alloy is a mixture of metals, or a metal mixed with a non-metal such as carbon

• The elements are physically combined but not chemically bonded

• Atoms of different elements are spread throughout the metallic lattice

• These atoms are held together by delocalized electrons, as in pure metals

• Metallic bonds are non-directional, allowing atoms of different sizes to occupy the lattice

Particle diagram of an alloy

Why do alloys have different properties to pure metals?

• In a pure metal, metal cations are arranged in regular layers

  • This allows them to slide past one another easily, causing the metal to be malleable

• In alloys, atoms of different sizes disrupt this regular pattern:

  • The distorted lattice makes it harder for the layers to slide

  • This gives alloys increased hardness and strength compared to pure metals

  • Alloys may also be more corrosion resistant or resistant to extreme temperatures

Examples of common alloys

Brass

• Component elements: copper and zinc

• Properties: Strong and corrosion resistant

• Uses: Door handles, hinges, musical instruments

Steel

• Component elements: Iron with carbon

  • Often includes other elements such as chromium, vanadium and molybdenum

• Properties: Very strong

• Uses: Construction, bridges, cars

Stainless steel

• Component elements: Iron, chromium, nickel, and carbon

• Properties: Corrosion resistant

• Uses: Cutlery, surgical instruments, cookware

Solder

• Component elements: Lead and tin

• Properties: Low melting point

• Uses: Joining metals in electrical circuits and jewellery

Bronze

• Component elements: Copper and tin

• Properties: Hard and corrosion resistant

• Uses: Medals, sculptures, ship fittings