Properties of Metals

General Physical Properties of Metals vs Non-Metals

1. Thermal Conductivity

• Metals:
  • Very good conductors of heat.
  • Reason: Metals have free-moving delocalised electrons in their metallic lattice. These electrons transfer kinetic energy rapidly from hot regions to cooler regions.
  • Examples:
    • Copper (Cu) is used in cooking pans because it quickly transfers heat from the heat source to the food.
    • Aluminium (Al) is used in heat sinks and cooking foil.
• Non-Metals:
  • Poor conductors of heat (insulators).
  • Reason: They lack free-moving electrons and heat can only be transferred through slow lattice vibrations (phonons).
  • Example: Wood, plastics, rubber.

2. Electrical Conductivity

• Metals:
  • Good conductors of electricity.
  • Reason: Presence of free electrons (delocalised electrons) that can move through the metallic structure when a potential difference is applied.
  • Examples:
    • Copper (Cu) in electrical wiring.
    • Aluminium (Al) in overhead power cables (lightweight and good conductor).
• Non-Metals:
  • Poor conductors (insulators).
  • Reason: No free electrons or ions to carry electrical current (except for some like graphite, which conducts due to delocalised electrons in its layered structure).
  • Example: Sulfur (S), diamond (C), plastic.

3. Malleability and Ductility

• Metals:
  • Malleable: Can be hammered or rolled into thin sheets.
  • Ductile: Can be drawn into wires.
  • Reason: Layers of positive metal ions can slide over each other without breaking metallic bonds, as the delocalised electrons hold the structure together.
  • Example:
    • Gold (Au) → extremely malleable, can be beaten into gold leaf.
    • Copper (Cu) → highly ductile, used in wiring.
• Non-Metals:
  • Brittle when solid.
  • Reason: Strong directional covalent bonds break when stress is applied, shattering the structure.
  • Example: Sulfur shatters easily when hit.

4. Melting Points and Boiling Points

• Metals:
  • Generally high melting and boiling points.
  • Reason: Strong metallic bonds between positive ions and delocalised electrons require a large amount of energy to break.
  • Exceptions: Mercury (Hg) is liquid at room temperature, and alkali metals have relatively low melting points compared to other metals.
• Non-Metals:
  • Generally low melting and boiling points (if molecular).
  • Reason: Weak intermolecular forces between molecules require little energy to overcome.
  • Exceptions: Non-metals with giant covalent structures (diamond, silicon) have very high melting points.

General Chemical Properties of Metals

1. Reaction with Dilute Acids

• General reaction:
  metal + dilute acid → salt + hydrogen
  Example:
  • Mg + 2HCl → MgCl₂ + H₂
• Observation:
  • Effervescence (bubbles) of hydrogen gas.
  • Metal may dissolve or disappear.
• Reactivity:
  • Most reactive metals (e.g., Mg, Zn, Fe) react readily with acids.
  • Less reactive metals (e.g., Cu, Ag, Au) do not react.

2. Reaction with Cold Water

• Highly reactive metals (e.g., Group I alkali metals, Ca) react with cold water:
  • metal + water → metal hydroxide + hydrogen
    Example: 2Na + 2H₂O → 2NaOH + H₂
  • Observations: Effervescence, metal floats and moves on water, may produce heat and flame (Na, K).
• Moderately reactive metals (e.g., Mg) have little reaction with cold water.
• Less reactive metals (e.g., Cu) have no reaction.

3. Reaction with Steam

• Metals like magnesium, zinc, and iron react with steam to produce metal oxide and hydrogen gas:
  • metal + steam → metal oxide + hydrogen
    Example: Mg + H₂O (steam) → MgO + H₂
  • Observations: Metal glows, white solid forms, hydrogen gas is released.

4. Reaction with Oxygen

• General reaction:
  metal + oxygen → metal oxide
  Example:
  • 4Al + 3O₂ → 2Al₂O₃
• Observations:
  • Metals burn with characteristic coloured flames:
    • Mg: bright white flame, white powder of MgO.
    • Na: yellow-orange flame, white Na₂O powder.
    • Cu: red-brown CuO forms.
• Oxide type:
  • Most metals form basic oxides.
  • Some metals (e.g., Al, Zn) form amphoteric oxides.

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