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.