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Materials: Metals and Non-metals Notes for CBSE Class 8 based on NCERT

Important topics covered in Materials: Metals and Non-metals

  • Introduction
  • Physical properties
  • Conductivity
  • Chemical properties
  • Reactivity
  • Difference between metals and non-metals
  • Uses

Introduction to metals and non-metals:

  • All the materials present around us is classified into two categories. They are metals and non-metals.
  • We can distinguish metals and non-metals on the basis of their physical properties.

Metals:

metals

  • Those materials which possess the characteristics of being hard, shiny, malleable, fusible, ductile etc. are termed as metal.
  • Iron, gold, silver, aluminium, copper etc. are some examples of metals.

Physical properties of metal:

  • Lustrous:
    lusturous metal
    The shine on metallic surface is said to be metallic lustre. Almost all metals show lustre. Gold and silver have enough lustre.
  • Malleability:
    malleability of metal
    The property of metal by which it can be beaten into thin sheets is said to be malleability. Silver metal is beaten into thin sheets as we see in decorating sweets.
  • Ductility:
    ductile metals
    The property of metals by virtue of which they can be drawn into wires is said to be ductility. Copper and iron show ductility.
  • Conductivity:
    conductor
    Metals are good conductor of heat and electricity. Metals like an iron rod, copper wire etc. are some examples of metals which are a good conductor of heat and electricity.
  • Sonorous:
    sonorous

    The property of material by the virtue of which it can produce sound on beating said to be sonorous. Ringing of bell is an example of sonorous.
  • Metals like sodium, potassium are so soft that they can be cut with a knife.
  • Mercury is the only metal which is present in liquid state at room temperature.

Chemical Properties of metals:

Metals show some common chemical properties. They are:

Reaction with oxygen:

Metals + Oxygen → Metallic oxides

  • Metals on reacting with oxygen forms metallic oxides.
  • Metallic oxides so formed are basic in nature.
  • Metals except for gold and silver (which are noble metals) reacts with oxygen to form metallic oxide.
  • Rusting of iron, copper etc. are examples of oxidation of metals.
  • Fe + 2O2 →Fe2O3 & 2Cu+ O2 → 2CuO

Reaction with Water:

Metals + Water → Metallic oxides + H2

  • Metals react with water to produce metal hydroxides and hydrogen gas.
  • Some metals like sodium react vigorously with water. So it is stored in kerosene.
  • Potassium (K) and Calcium (Ca) are also active metals and react with water at room temperature.
  • Some metals such as iron react very slowly with water.

Reaction with acids:

Metals + Dilute acid → Metal salt + Hydrogen gas

  • Metals react with to liberate hydrogen and corresponding salt of the metal.
  • A pop sound is heard after reaction which shows hydrogen gas has evolved.
  • Copper doesn’t show any reaction with hydrochloric acid while it reacts with sulfuric acid.
  • When metals are reacted with HNO3 it doesn’t evolve Hydrogen gas. HNO3 is a strong oxidizing • agent it oxidises H2.
  • Aqua Regia: The solution of HCl and HNO3 in the ratio 3:1 respectively are said to be aqua regia. It dissolves gold and platinum.

Reaction with bases:

Metals + Bases → H2 gas

  • Metals react with bases to produce Hydrogen gas.
  • As seen, when metals react with sodium hydroxide (NaOH) and releases H2

Displacement Reaction:

  • When a metal replaces other metal from its compound during reaction then it is said to be displacement reaction.
  • A metal with higher reactivity displaces a metal of lower reactivity.
  • A series of metals are arranged on the basis of reactivity and is said to be reactivity series.
  • As example: zinc (Zn) replaces copper from copper sulphate solution.
    CuSO4 + Zn → ZnSO4 + Cu

Uses of Metals:

  • Metals are generally used in making machinery.
  • Copper is used in making conducting wires, utensils and much more.
  • Gold and silver are used in making ornaments.
  • Silver is also used in making coins, thin wires, table cutlery etc.
  • Iron is used for construction of ships, automobiles, bridges etc.
  • Tin is used for making alloys and tinning food cans.
  • We use lead to make batteries and alloys.
  • In fireworks, magnesium is used.
  • Mercury is used in thermometers and amalgams.

Non-Metals:

  • Those materials which don’t possess the characteristics of metals such as lustrous, malleability, ductility etc. are said to be non-metals.
  • Coal, sulfur, carbon etc. are some examples of non-metals.

Physical properties of Non-metals:

  • Non-metals are observed in all three states i.e. solid, liquid, gases.
  • Iodine being a non-metal is lustrous.
  • Carbon exist in many forms i.e. carbon has allotropes.
  • Diamond is the hardest non-metal.
  • Graphite being non-metal conducts electricity.
  • Graphite is also used as a lubricant.

Chemical properties of Non-metals:

Let’s discuss the chemical properties of non-metals:

Reaction with oxygen:

Non-metals + Oxygen → Non-metallic oxide

  • Non-metals also produce its oxide.
  • But non-metallic oxide is acidic or neutral in nature.

Reaction with water:

Non-metal + water → normally no reaction

  • Generally, non-metals do not react with water.
  • But some non-metals like phosphorous which is very reactive in air.
  • Phosphorous is kept in water to prevent explosion.

Reaction with acid:

Non-metal + Acid → No reaction

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

Reaction with bases:

  • Reaction of non-metals with bases is complex.
  • We will read it in higher sections.

Uses of non-metals:

  • Oxygen which is non-metal is the life support system of living organisms, as oxygen is required for respiration which is one of the main life processes.
  • Green plants to carry out photosynthesis with the help of Carbon dioxide.
  • Some non-metals like nitrogen and phosphorus are used in fertilisers for better plant growth.
  • Chlorine (CI2) is used in water purification system.
  • Graphite is used as lubricant, in pencils, in nuclear reactor etc.
  • Non-metal Helium is used in weather observation balloon.
  • Argon is filled in electric bulbs.

Alloy:

  • The homogeneous mixture of two metals is said to be alloy.
  • Alloying is done to enhance the property of metals.
  • Aluminium alloy is very useful as they are light as well as strong.
  • Iron and carbon in a fixed ratio make up steel.
  • Example of alloys of zinc is Bonze, Brass, German silver etc.

Differences between Metals and Non-metals:

Metals Non-metals
Metals are lustrous. Non-metals are non-lustrous
except for iodine 
They are a good conductor of
heat and electricity.
They are a poor conductor of
heat and electricity
They are malleable. They are brittle.
Metals are present mainly in
solid form at 
room temperature.
Except for Mercury which exists
in liquid form at room temperature.
They are present in either
solid or liquid
form
at room temperature.
Metals are ductile. They are non-ductile.
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