Metals

Properties

Metals are:

  • solids with high melting and boiling points
  • malleable
  • good conductors of electricity and heat

Alloys

Alloys are mixtures of a metal with other elements.

Alloys are used instead of pure metals because they may be:

  • more resistant to corrossion
  • stronger
  • harder
  • less dense

Alloys contain atoms of different sizes which distorts the regular arrangement of atoms in metals. This makes it harder for layers to slide over each other.

Reactivity Series

The reactivity series is a list of metallic elements ranked their reactivity. Elements that are more reactive can displace less reactive elements from their compounds, forming a new compound.

The reactivity series (starting with the most reactive element) is:

  • Group 1
    • Potassium
    • Sodium
  • Group 2
    • Calcium
    • Magnesium
  • Group 3
    • Aluminium
  • Carbon
  • Transition Metals
    • Zinc
    • Iron
  • Hydrogen
  • Precious Metals
    • Copper
    • Silver
    • Gold
    • Platinum

Group 1 and 2 react violently with water to produce hydrogen gas. Transition metals will not react with water under normal conditions but will react with steam. Precious metals are less reactive than hydrogen and will not react with water or steam.

Only elements less reactive than carbon can be extracted from their ores through reduction with carbon.

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Typically, less reactive metals are more expensive. These metals are often found as pure elements in their ores and not as compounds.

Reactivity can be described as the tendency of a metal to form a positive ion.

Metal Extraction

The extraction of metals from their ores is dependent on the reactivity series.

Reduction with Carbon

Some metals are extracted using carbon. One such metal is iron.

  • Hematite is loaded into a blast furnace
  • Iron is extracted from hematite using carbon monoxide
  • Calcium carbonate is used to remove impurities from the ore
  • Calcoum carbonate thermally decomposes into calcium oxide which forms slag
  • Slag is separately removed from the furnace

Important reactions take place inside the blast furnace. Coke is used to make carbon monoxide.

C + O2 → CO2
C + CO2 → 2CO

Hematite is reduced by carbon monoxide to extract pure iron.

Fe2O3 + 3CO → 2Fe + 3CO2

Calcium carbonate used to remove acidic impurities decomposes due to high temperatures.

CaCO3 → CaO + CO2

Calcium oxide reacts with silica impurities to form slag.

CaO + SiO2 → CaSiO3

Electrolysis

Metals more reactive than carbon are extracted using electrolysis. For example, aluminium is extracted from bauxite by electrolysis. Aluminium oxide has a high melting point that needs to be lowered by mixing it with cryolite.

Recycling

It is important to recycle metals because metal ores are a finite resource.

Uses of Metals

Aluminium

Aluminium is used in:

  • aircraft parts because of its strength and low density
  • food containers because of its resistance to corrosion

Aluminium has an apparent unreactivity and resistance to corrision because an oxide layer that adheres to the surface of aluminium. This layer prevents further oxidation.

Steel

Mild steel is used in car bodies and machinery while stainless steel is used in cutlery. Steel is an alloy that is strogner and has a higher melting point than its constituents.

Zinc

Zinc is used for:

  • galvanising steel to prevent corrosion
  • making brass by mixing it with copper