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.