Class 8 Materials : Metals and Non-metals Notes

Materials : Metals and Non-metals Notes

Physical properties of metals:-

  • They are solid in state except mercury (liquid).
  • They are malleable i.e., they can be beaten into thin sheet. Gold and silver are most malleable metals.
  • They are ductile i.e., they can be drawn into thin wire. Gold is the most ductile metal.
  • They are good conductors of heat and electricity. Silver and copper are the best conductors of heat while lead and mercury are poor conductors of heat.
  • They have high melting and boiling point except gallium and cesium.
  • They are very hard except lithium, sodium and potassium.
  • They are lustrous i.e., they have shining surface.
  • They are sonorous i.e., they produce a ringing sound on striking a hard surface.

Malleability:- The property of a metal by which it can be beaten into thin sheet is called malleability.

Ductility:- The property of a metal by which it can be drawn into thin wire is called ductility.

Sonority:- The property of a metal by which it produces a ringing sound on striking a hard surface is called sonority.

Lustre:- The shining property of metals is called lustre.

Physical properties of non-metals:-

  • They can be solid, liquid or gas.
    ➢ Bromine is the only non-metal which is liquid.
  • They are non-malleable.
  • They are non-ductile.
  • They are bad conductors of heat and electricity.
    ➢ Graphite, a form of carbon is the only non-metal which is a good conductor of electricity.
  • They have varying hardness and are generally less hard.
    ➢ Diamond, a form of carbon is a non-metal which is the hardest natural substance known.
  • They have low melting and boiling point.
    ➢ Diamond has high melting and boiling point.
  • They are non-lustrous.
    ➢ Iodine is the only non-metal which is lustrous.
  • They are non-sonorous.

Chemical properties of metals of Metals and Non-metals:-

Reaction of metals with oxygen:-

  • Metal + Oxygen → Metal Oxide
    ➢ 4Na + O2 → 2Na2O
    ➢ 2Mg + O2 → 2MgO
  • Metal oxides are generally basic in nature and turns red litmus blue.
  • Metal oxide in water gives metal hydroxide.
    ➢ MgO + H2O → Mg(OH)2

Reaction of non-metals with oxygen:-

  • Non-metal + Oxygen → Non-metal Oxide
    ➢ S + O2 → SO2 (Sulphur dioxide)
    ➢ C + O2 → CO2 (Carbon dioxide)
  • Non-metal oxides are generally acidic in nature and turns blue litmus red.
  • Non-metal oxide in water gives an acid.
    ➢ SO2 + H2O → H2SO3 (Sulphurous acid)
    ➢ CO2 + H2O → H2CO3 (Carbonic acid)

Reaction of metals with water:-

  • Reaction of metals like sodium and potassium is so violent and exothermic that the evolved hydrogen catches fire.
    ➢ 2Na + 2H2O → 2NaOH + H2 + Heat
    ➢ 2K + 2H2O → 2KOH + H2 + Heat
  • Some other metals like aluminium, iron, zinc etc react with water slowly.

Reaction of non-metals with water:-

  • Generally, non-metals do not react with water.
  • Phosphorus is a very reactive non-metal and catches fire in air. So, it is stored in water.

Reaction of metals with acids:-

  • Metal + Dilute acid → Salt + Hydrogen
    ➢ Mg + 2HCl → MgCl2 + H2
    ➢ 2Al + 6HCl → 2AlCl3 + 3H2
  • Hydrogen gas gives pop sound when a burning match stick is brought near it.
  • Copper does not react with dilute hydrochloric acid even on heating but it reacts with sulphuric acid.

Reaction of non-metals with acids:-

  • Generally, non-metals do not react with acids.

Displacement reaction:- 

The reaction in which highly reactive metal displaces less reactive metal from its salt solution is called displacement reaction.

  • Metal A + Salt solution of metal B → Salt solution of metal A + Metal B
    ➢ 2K + FeSO4 → K2SO4 + Fe
    ➢ Zn + CuSO4 → ZnSO4 + Cu

Some uses of coomon metals:-

  • Iron is the most widely used metal. It is used for making cooking vessels, stoves, toys, tools, pipes, agricultural implements, chains, wires, nails, bolts, electromagnets, etc.
  • Aluminiium is a very light metal. so, It is used for making aircraft bodies. It is also used for making cooking vessels and for packaging food items and medicines.
  • Copper is used for making electrical cables, other electrical goods and cooking vessels.
  • Silver is used for making jewellery, decoration pieces, tableware, etc.

Some uses of non-metals:-

  • Nitrogen is used in fertilisers.
  • Phosphorus is used in matchbox industry and in fertilisers.
  • Iodine is used as an antiseptic.
  • Sulphur is used for making fire crackers, gun powder and sulphuric acid.
  • Oxygen is used breathing.
  • Diamond is used in making jewellery, in cuting glass and for grinding of tools.
  • Graphite is used in batteries and in pencils.

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