Materials: Metals and Non—Metals Class 8 Notes NCERT and MCQs

23-08-2023 17:12 PM IST Yadvendra Singh

This chapter discusses physical and chemical properties of metals and non-metals. It also enlists their uses.

What are Metals and Non-metals?

Metals are materials that are hard, lustrous, malleable, ductile, sonorous and good conductors of heat and electricity. Examples of metals are iron, copper, aluminium, calcium, magnesium, etc. Non-metals do not have properties possessed by metals. Examples of non-metals are sulphur, carbon, oxygen, phosphorus, etc. Non-metals like coal and sulphur are soft and dull in appearance.

Physical properties of metals and non-metals

• Malleability:  The property of metals by which they can be beaten into thin sheets is called malleability. Generally, metals are malleable. Non-metals do not have this property.
• Conduction of heat and electricity: Generally, metals are good conductors of heat and electricity but non-metals are poor conductors.
• Ductility: The property of metal by which it can be drawn into wires is called ductility. Generally, metals are ductile. Non-metals do not have this property.
• Sonorous: The things made of metals produce a ringing sound when struck hard. Since metals produce ringing sounds, they are said to be sonorous.
• Lustre: Metals are lustrous whereas non-metals have no lustre (glow).

Chemicalproperties of metals and non-metals

• Oxide formation: On burning, metals react with oxygen to produce metal oxides which are generally basic in nature. Their oxides turn red litmus paper blue.  Non-metals react with oxygen to produce non- metallic oxides which are generally acidic in nature. Their oxides turn blue litmus paper red.

When sulphur dioxide is dissolved in water sulphurous acid is formed.

Sulphur dioxide (SO₂) + Water (H₂O) → Sulphurous acid (H₂SO₃)

Sulphurous acid turns blue litmus paper red.

• Reaction with water: Some metals react with water to produce metal hydroxides and hydrogen gas. Example: When a copper vessel is exposed to moist air for long, a dull green coating appears on its surface. This is due to the formation of Copper Hydroxide and Copper Carbonate.

2Cu + H₂O + CO₂ + O₂  → Cu(OH)₂ + CuCO₃

Generally, non-metals do not react with water.

• Reaction with acid: Metals react with acids and produce metal salts and hydrogen gas. Generally, non-metals do not react with acids.
• Reaction with bases: Metals react with bases to produce hydrogen gas. Reactions of non-metals with bases are complex.
• Displacement reactions: More reactive metals displace less reactive metals from their compounds in aqueous solutions. When Zn reacts with CuSO₄ (Copper Sulphate), the blue color of the copper sulphate disappears and a powdery mass of copper is deposited at the bottom.

CuSO₄ + Zn → ZnSO₄ + Cu

NOTE: A more reactive metal can replace a less reactive metal, but a less reactive cannot replace a more reactive metal. So, if ZnSO₄ is mixed with Cu, there will be no change.

Uses of metals and non-metals

• Metals are used in making machinery, automobiles, aeroplanes, trains, satellites, industrial gadgets, cooking utensils, water boilers, etc.
• Non-metal is essential for our Life. All living beings inhale it during breathing- Oxygen
• Non-metals are used in fertilisers to enhance the growth of plants. Nitrogen and Phosphorus are widely used in making fertilizers.
• Non-metals are used in water purification process -Chlorine
• Non-metal is used in the purple coloured solution which is applied on wounds as an antiseptic- Iodine
• Non-metals are used in crackers- Sulphur and Phosphorus

Important Facts related to Metals and Non-Metals

• Sodium metal is very reactive and reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. Sodium is, therefore, stored in kerosene.
• Iron reacts with water slowly.
• Non-metals may be very reactive in air. Such non-metals are stored in water. For example, phosphorus is a very reactive non-metal. It catches fire if exposed to air. Therefore, Phosphorus is stored in water.
• Metals like sodium and potassium are soft and can be cut with a knife.
• Mercury is the only metal that is found in liquid state at room temperature.
• There are no more than 94 naturally occurring elements.  
• Most of the elements are metals. The remaining are either non-metals or metalloids.
• Metalloids possess the character of both metals and non-metals.

MCQs based on NCERT Class 8 Science Chapter 4 Materials: Metals and Non-Metals

1. What is the nature of metal oxides?

a. Acidic

b. Basic

c. May be acidic or basic

d. Neither acidic nor basic

Ans. b

Explanation:

 On burning, metals react with oxygen to produce metal oxides which are generally basic in nature. Their oxides turn red litmus paper blue.  Non-metals react with oxygen to produce non- metallic oxides which are generally acidic in nature. Their oxides turn blue litmus paper red.

2.  Which of the following metals is stored in Kerosene?

a. Aluminium

b. Calcium

c. Magnesium

d. Sodium

Ans. d

Explanation:

Sodium metal is very reactive and reacts vigorously with oxygen and water. A lot of heat is generated in the reaction. Sodium is, therefore, stored in kerosene.

3. Which of the following metals catches fire if exposed to air?

a. Sulphur

b. Carbon

c. Oxygen

d. Phosphorus

Ans. d

Explanation:

Some non-metals may be very reactive in air. Such non-metals are stored in water. For example, phosphorus is a very reactive non-metal. It catches fire if exposed to air.

4. Which of the following elements does not possess property of malleability?

a. Copper

b. Aluminium

c. Calcium

d. Sulphur

Ans. d

Explanation:

The property of metals by which they can be beaten into thin sheets is called malleability. Generally, metals are malleable. Non-metals do not have this property. Sulphur is a non-metal. Therefore, does not possess the property of malleability.

5.  Which of the following shows properties such as ductility and lustre?

a. Copper

b. Sulphur

c. Carbon

 d. Phosphorus

Ans: a

Explanation:

The property of metal by which it can be drawn into wires is called ductility. Generally, metals are ductile. Non-metals do not have this property.  Metals are lustrous whereas non-metals have no lustre (glow). Copper is a metal. Hence, it shows properties such as ductility and lustre.

6. Which of the following can be beaten into thin sheets?

a. Zinc

b. Phosphorus

c. Sulphur

d. Oxygen

Ans: a

Explanation:

Metals possess the property of being beaten into sheets. Among the options, Zinc is a metal and can be beaten into sheets.

7. Which of the following statements is correct?

a. All metals are ductile.

b. All non-metals are ductile.

c. Generally, metals are ductile.

d. Some non-metals are ductile.

Ans: c

Explanation:

Generally, metals are ductile, except Mercury. Non-metals do not have this property.