Metals and Structures

Metals and Structures

Metals

  • Many everyday items are made of metal, including wiring, radiators, hot-water tanks, and cutlery.
  • Different metals possess properties suited for various uses.
  • Metallic bonding is distinct from ionic and covalent bonding.
Metallic Bonding
  • The properties of metals include:
    • High melting and boiling points
    • Good electrical and thermal conductivity
    • Hardness and density
    • Malleability (can be hammered into shapes)
    • Ductility (can be drawn into wires)
  • Metal atoms/ions are held together by a 'sea' of electrons.
  • Each metal atom contributes electrons from its outer shell to this 'sea' or 'cloud' of electrons.
  • These free electrons can drift throughout the metal structure.
  • The movement of free electrons explains electrical conductivity: when a metal is subjected to a potential difference (positive and negative ends), electrons move towards the positive charge.
  • Free electrons also facilitate rapid heat transfer through metals.

Explaining the Properties of Alloys

  • In pure metals, atoms are of uniform size, allowing layers to slide over each other easily when a force is applied (malleability and ductility).
  • Alloys are formed by adding atoms of a different size to a pure metal, disrupting the regular arrangement.
  • This disruption impedes the easy sliding of layers, making the alloy harder and stronger than the original metal.

Alloys

  • Airplanes are primarily made from aluminum alloys.
  • Pure aluminum is not strong enough to withstand the stress on airplane wings during flight.
  • Alloys combine the low density of aluminum with increased strength.
  • An alloy is a mixture of metals, created by mixing molten metals together.
  • The metals do not react chemically; it's a mixture, not a compound.
Experiment 23.2: Bubble Bath!
  • This experiment demonstrates the structure of metals and alloys using bubbles.
  • Small bubbles in a dish represent atoms in a metal's close-packed structure.
  • Rows of bubbles line up, and when a bubble bursts, the rows easily slide past each other.
  • Injecting a larger bubble simulates the addition of a different metal atom, creating an alloy.
  • This disrupts the regular pattern of bubbles, illustrating how alloys have a different structure from pure metals.