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.
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.