नोट: इस लेख का हिंदी संस्करण भी उपलब्ध है।
Chapter-4 : Metals and Non-metals
Introduction
Everything around us is made up of materials. From the chair you sit on to the water you drink, each object is made of substances that have specific properties. In Class 7 Science (NCERT), one of the most important chapters is “The World of Metals and Non-metals”, which helps students understand how different materials behave and why they are used for specific purposes.
Metals and non-metals are two major categories of elements. Their properties determine their uses in everyday life. This chapter builds a strong foundation for future chemistry topics and helps students connect science with real-life applications.
Classification of Materials
Materials can be classified in many ways, but one of the most important classifications is:
- Metals
- Non-metals
This classification is based on physical properties (like hardness, shine) and chemical properties (like reactions with oxygen, water, and acids).
What are Metals?
Metals are substances that generally:
- Have a shiny surface
- Are hard and strong
- Conduct heat and electricity
- Can be shaped into sheets and wires
Examples of Metals
- Iron
- Copper
- Aluminium
- Gold
- Silver
Metals are widely used in industries, construction, and daily life due to their strength and conductivity.
What are Non-metals?
Non-metals are substances that generally:
- Do not have shine
- Are soft or brittle
- Are poor conductors of heat and electricity
- Cannot be shaped easily
Examples of Non-metals
- Oxygen
- Nitrogen
- Carbon
- Sulphur
- Chlorine
Non-metals play an important role in life processes and environmental balance.
Physical Properties of Metals
Understanding the physical properties helps us identify metals easily.
1. Lustre (Shiny Surface)
Metals have a natural shine called lustre.
- Gold and silver are highly shiny.
- This property makes metals suitable for jewellery and decoration.
2. Hardness
Most metals are hard and strong.
- Iron is very hard and used in construction.
- However, exceptions exist:
- Sodium and potassium are soft and can be cut with a knife.
3. Malleability
Metals can be hammered into thin sheets.
- Aluminium is used to make foil.
- Gold can be beaten into very thin sheets for decorative purposes.
4. Ductility
Metals can be drawn into wires.
- Copper is used in electric wires.
- Aluminium is also used in transmission lines.
5. Conductivity
Heat Conductivity
Metals allow heat to pass through them easily.
- Used in cooking utensils
Electrical Conductivity
Metals conduct electricity well.
- Used in electrical wiring
6. Sonority
Metals produce a ringing sound when struck.
- Used in bells, musical instruments
Physical Properties of Non-metals
Non-metals show properties opposite to metals.
1. Non-lustrous (Dull)
Most non-metals are dull in appearance.
- Example: Coal, sulphur
2. Softness
Non-metals are usually soft and not strong.
- They break easily and cannot be used for heavy structures.
3. Non-malleable
They cannot be hammered into sheets.
4. Non-ductile
They cannot be drawn into wires.
5. Poor Conductors
Non-metals do not conduct heat or electricity.
Exception
- Graphite conducts electricity even though it is a non-metal.
6. Non-sonorous
They do not produce sound when struck.
Chemical Properties of Metals
Chemical properties describe how metals react with other substances.
1. Reaction with Oxygen
Metals react with oxygen to form metal oxides.
Example:
Magnesium + Oxygen → Magnesium oxide
- Metal oxides are usually basic in nature.
- They can react with acids to form salt and water.
2. Reaction with Water
Some metals react with water to form:
- Metal hydroxide
- Hydrogen gas
Example:
Sodium + Water → Sodium hydroxide + Hydrogen
- This reaction can be very fast and sometimes dangerous.
3. Reaction with Acids
Metals react with acids to produce:
- Salt
- Hydrogen gas
Example:
Zinc + Hydrochloric acid → Zinc chloride + Hydrogen
This is an important reaction often tested in exams.
Chemical Properties of Non-metals
1. Reaction with Oxygen
Non-metals react with oxygen to form non-metal oxides.
Example:
Sulphur + Oxygen → Sulphur dioxide
- These oxides are generally acidic in nature.
2. Reaction with Water
Non-metals generally do not react with water.
3. Reaction with Acids
Non-metals do not react with acids.
Uses of Metals in Everyday Life
Metals are used in many areas due to their useful properties.
1. Construction
- Iron and steel are used in buildings, bridges, and machines.
2. Electrical Wiring
- Copper and aluminium are used because they conduct electricity.
3. Cooking Utensils
- Aluminium and stainless steel are used due to heat conductivity.
4. Jewellery
- Gold and silver are used because they are shiny and do not corrode easily.
5. Transport
- Metals are used in making vehicles, trains, and airplanes.
Uses of Non-metals in Everyday Life
Non-metals are equally important.
1. Oxygen
- Essential for breathing
2. Nitrogen
- Used in fertilizers for plant growth
3. Carbon
- Used as fuel (coal)
- Graphite used in pencils
4. Chlorine
- Used to purify drinking water
5. Sulphur
- Used in medicines and matches
Difference Between Metals and Non-metals
| Property | Metals | Non-metals |
|---|---|---|
| Appearance | Shiny | Dull |
| Hardness | Hard | Soft |
| Malleability | Can be hammered into sheets | Cannot be hammered |
| Ductility | Can be drawn into wires | Cannot be drawn |
| Conductivity | Good conductors | Poor conductors |
| Sound | Sonorous | Non-sonorous |
Important Exceptions
Students must remember these exceptions for exams:
- Mercury is a metal but is liquid at room temperature.
- Sodium and potassium are metals but are soft.
- Graphite is a non-metal but conducts electricity.
- Iodine is a non-metal but has lustre.
Precautions While Handling Metals
Some metals like sodium and potassium are very reactive.
- They are stored in kerosene to prevent reaction with air and water.
- Always handle chemicals carefully in laboratories.
Why This Chapter is Important
This chapter is important because:
- It explains materials used in daily life
- It builds basic chemistry concepts
- It is useful for exams and competitive tests
- It helps understand future topics like reactions and elements
Real-Life Applications
- Electric wires → Copper
- Cooking utensils → Aluminium
- Jewellery → Gold, Silver
- Pencil lead → Graphite
- Water purification → Chlorine
Quick Revision Notes
- Metals are shiny, hard, and good conductors.
- Non-metals are dull, soft, and poor conductors.
- Metals form basic oxides.
- Non-metals form acidic oxides.
- Metals react with acids to release hydrogen gas.
- Non-metals generally do not react with acids.
Conclusion
The chapter “The World of Metals and Non-metals” in Class 7 NCERT Science is a fundamental topic that helps students understand the nature of materials around them. By learning the properties, reactions, and uses of metals and non-metals, students can clearly see how science is connected to everyday life.
This knowledge not only helps in exams but also builds a strong base for higher studies in chemistry and science.
Chapter-1 | Chapter-2 | Chapter-3 | Chapter-4 | Chapter-5 | Chapter-6 | Chapter-7 | Chapter-8 | Chapter-9 | Chapter-10 | Chapter-11 | Chapter-12 | General Science Quiz
Practice Exercise
10 Important Questions with Explained Answers
1. What are metals? Write their main properties.
Answer:
Metals are substances that are generally shiny, hard, malleable, ductile, and good conductors of heat and electricity.
Explanation: These properties make metals useful for making utensils, wires, machines, and construction materials.
2. What are non-metals? State their properties.
Answer:
Non-metals are substances that are generally dull, soft or brittle, and poor conductors of heat and electricity.
Explanation: Non-metals are used in fertilizers, medicines, and as gases essential for life.
3. What is malleability? Explain with an example.
Answer:
Malleability is the property of metals by which they can be beaten into thin sheets.
Example: Aluminium foil
Explanation: This property is useful in packaging and making sheets.
4. What is ductility?
Answer:
Ductility is the property of metals by which they can be drawn into thin wires.
Example: Copper wires
Explanation: This property is important for electrical wiring.
5. Write any two differences between metals and non-metals.
Answer:
- Metals are shiny, while non-metals are dull.
- Metals are good conductors, while non-metals are poor conductors.
Explanation: These differences help in identifying and using materials correctly.
6. What happens when metals react with oxygen?
Answer:
Metals react with oxygen to form metal oxides.
Explanation: These oxides are generally basic in nature.
7. What happens when non-metals react with oxygen?
Answer:
Non-metals react with oxygen to form non-metal oxides.
Explanation: These oxides are usually acidic in nature.
8. What happens when metals react with acids?
Answer:
Metals react with acids to produce salt and hydrogen gas.
Explanation: This reaction is commonly observed in laboratories.
9. Why is graphite considered special?
Answer:
Graphite is a non-metal, yet it conducts electricity.
Explanation: This makes it an important exception among non-metals.
10. Why is sodium stored in kerosene?
Answer:
Sodium is highly reactive and reacts quickly with air and water.
Explanation: Storing it in kerosene prevents unwanted reactions.
Fill in the Blanks
- Metals are generally _______ and _______.
- Non-metals are _______ conductors of heat and electricity.
- Metals react with acids to produce _______ gas.
- _______ is a non-metal that conducts electricity.
- Metal oxides are generally _______ in nature.
Answers:
- shiny, hard
- poor
- hydrogen
- Graphite
- basic
True / False
- All metals are hard.
- Non-metals do not produce sound.
- Metals are poor conductors of electricity.
- Graphite conducts electricity.
- Non-metals react with acids.
Answers:
- False
- True
- False
- True
- False
Assertion–Reason Questions
1.
Assertion (A): Metals are good conductors of electricity.
Reason (R): Metals have free electrons.
Answer: Both A and R are true, and R is the correct explanation of A.
2.
Assertion (A): Non-metals are shiny.
Reason (R): They have metallic properties.
Answer: Both A and R are false.
3.
Assertion (A): Sodium is stored in kerosene.
Reason (R): It reacts quickly with water.
Answer: Both A and R are true, and R is the correct explanation of A.
4.
Assertion (A): Metal oxides are basic.
Reason (R): They form acids when dissolved in water.
Answer: A is true, R is false.
5.
Assertion (A): Graphite conducts electricity.
Reason (R): It is a non-metal.
Answer: A is true, R is false.
Free Quiz On : Class 7 Science- Metals & Non-Metals
Iron is a metal with typical metallic properties.
Ductility means the ability to form wires.
Sulphur is a typical non-metal.
Metals conduct both heat and electricity efficiently.
Graphite is an exception among non-metals.
Metals form oxides when reacting with oxygen.
Non-metals are generally brittle in nature.
Mercury is the only liquid metal at room temperature.
Hydrogen gas is released in this reaction.
Sodium is highly reactive and must be protected.
Quiz Results
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