Chapter 4: Materials: metals and non-metals

These NCERT Class 8 Science Chapter 4 notes explain the properties of metals and non-metals in a clear and structured way. The chapter focuses on how different materials behave based on their physical and chemical properties.

It discusses characteristics like lustre, malleability, ductility, conductivity and sonority. It also explains chemical reactions of metals and non-metals with oxygen, water and acids, along with corrosion and rusting.

Chapter 4 – Materials: Metals and Non-Metals is important for understanding the classification of substances and their practical uses. It builds a strong base for school examinations and foundation level competitive preparation.

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1. Introduction: what are metals and non-metals?

• All substances around us are made of materials.
• Materials are broadly classified into metals and non-metals.
• Metals and non-metals differ in their physical and chemical properties.
• We choose materials based on their properties and uses.
• For example, a steel spoon is a metal, while a wooden spoon is a non-metal.

2. Physical properties of metals

• Metals have lustre, which means they are shiny like gold and silver.
• Most metals are hard, but sodium and potassium are soft exceptions.
• Metals are malleable, so they can be beaten into thin sheets like aluminium foil.
• Metals are ductile, meaning they can be drawn into wires like copper wires.
• Metals are good conductors of heat and electricity and are sonorous, producing a ringing sound when struck.

3. Physical properties of non-metals

• Non-metals are generally dull in appearance, except iodine.
• They are poor conductors of heat and electricity.
• Non-metals are brittle, so they break easily when hammered.
• They are not sonorous and do not produce a ringing sound.
• Examples include sulphur, carbon and oxygen.

4. Comparison between metals and non-metals

• Metals are shiny due to lustre, while non-metals are usually dull.
• Metals are mostly hard, whereas non-metals are mostly soft.
• Metals have good conductivity, while non-metals are poor conductors.
• Metals are malleable and ductile, but non-metals are not.
• Metals are sonorous, while non-metals are non-sonorous.

5. Chemical properties of metals

• Metals react with oxygen to form metal oxides, which are generally basic in nature.
• For example, magnesium reacts with oxygen to form magnesium oxide.
• Some metals react with water to form metal hydroxide and hydrogen gas.
• Sodium reacts violently with water, while iron reacts slowly.
• Metals react with acids to produce salt and hydrogen gas, which burns with a pop sound.

6. Chemical properties of non-metals

• Non-metals react with oxygen to form non-metal oxides.
• These oxides are generally acidic in nature.
• For example, sulphur reacts with oxygen to form sulphur dioxide.
• Non-metals usually do not react with water like metals do.
• Their chemical behaviour is different from metals.

7. Uses of metals

• Iron is used in construction work and making tools.
• Copper is used in electrical wires because of high conductivity.
• Aluminium is used in aircraft bodies due to its light weight.
• Gold is used in jewellery because of its lustre and resistance to corrosion.
• Some metals are mixed to form alloys to improve their properties.

8. Uses of non-metals

• Oxygen is essential for breathing.
• Nitrogen is used in making fertilisers.
• Carbon is used as a fuel in the form of coal.
• Sulphur is used in medicines and chemicals.
• Non-metals play an important role in daily life.

9. Corrosion and rusting

• Corrosion is the slow destruction of metals by air and moisture.
• Rusting is a type of corrosion that occurs in iron.
• Rusting happens when iron reacts with oxygen and water.
• Corrosion weakens metals and reduces their usefulness.
• Preventing corrosion increases the life of metal objects.

10. Prevention of corrosion

• Painting metal surfaces prevents contact with air and moisture.
• Oiling and greasing protect metal surfaces from rusting.
• Galvanisation involves coating iron with zinc to prevent corrosion.
• Electroplating coats one metal with another to improve protection and appearance.
• For example, bicycle chains are oiled to prevent rusting.

11. Key exam-oriented keywords explained

• Metals: Materials that are generally shiny, hard and good conductors of heat and electricity.
• Non-metals: Materials that are usually dull, brittle and poor conductors.
• Lustre: The shiny appearance of metals.
• Malleability: Property of metals to be beaten into thin sheets.
• Ductility: Property of metals to be drawn into wires.
• Sonorous: Property of metals to produce a ringing sound when struck.
• Conductivity: Ability of a substance to allow heat or electricity to pass through it.
• Corrosion: Slow destruction of metals by air and moisture.
• Rusting: Formation of reddish-brown coating on iron due to reaction with oxygen and water.
• Galvanisation: Process of coating iron with zinc to prevent rusting.

12. One-page summary for quick revision

• Materials are classified into metals and non-metals based on properties.
• Metals are shiny, malleable, ductile and good conductors.
• Non-metals are generally dull, brittle and poor conductors.
• Metals and non-metals show different chemical reactions.
• Corrosion and rusting damage metals and can be prevented by protective methods.

Understanding NCERT Class 8 Science Chapter 4 is essential to learn how metals and non-metals differ in their properties and reactions. The chapter clearly explains corrosion, rusting and preventive measures.

The concepts help students understand material science basics and their applications in daily life. It is highly useful for school exams and foundation competitive preparation.

Continue reading NCERT Class 8 Science Chapter 5 – Coal and Petroleum to understand fossil fuels and natural resources.

FAQs

Q1. What are metals?
Metals are materials that are generally shiny, hard, malleable and good conductors of heat and electricity.

Q2. What are non-metals?
Non-metals are materials that are usually dull, brittle and poor conductors of heat and electricity.

Q3. What is corrosion?
Corrosion is the slow destruction of metals due to reaction with air and moisture.

Q4. What is rusting?
Rusting is the formation of iron oxide when iron reacts with oxygen and water.

Q5. Why is this chapter important for exams?
It explains physical and chemical properties of materials, which are important for school exams and foundation preparation.

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