Class 7 Science Chapter 4: The World of Metals and Non-metals | Complete NCERT Notes, Activities, Questions & Answers

Full Chapter Summary with Properties Tables, All Activities 4.1-4.8 Solved Step-by-Step, NCERT "Let Us Enhance Our Learning" Questions, 20+ Extra Practice Questions & Answers, Quick Revision Notes, Mnemonics, Real-Life Examples for CBSE Board Exams

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Categories: Class 7 Science, NCERT Notes, Metals and Non-metals, CBSE Exam Preparation, Science Study Guides, Curiosity Textbook, Properties of Metals, Rusting and Corrosion, Chapter 4 Notes, Activity Solutions, Revision Notes
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The World of Metals and Non-metals - Class 7 Science Chapter 4 Ultimate Study Guide 2025

The World of Metals and Non-metals

Chapter 4: Curiosity Textbook of Science - Grade 7 | Ultimate Study Guide | NCERT Class 7 Notes, Activities, Examples & Extra Q&A 2025

Full Chapter Summary & Detailed Notes - The World of Metals and Non-metals

Overview & Chapter Goal

  • Chapter Goal: Understand what metals and non-metals are, compare their properties, and see how these properties decide their uses in daily life. Focus on malleability, ductility, sonority, conduction, corrosion, and importance of non-metals.
  • Story Start: Yashwant and Anandi visit an ironsmith in Rajasthan and watch how an iron block is heated and beaten into tools like axes and spades. This leads to questions like: “Can all materials be beaten into sheets like this?”
  • Exam Focus (2025): Properties table (lustrous/non-lustrous, malleable/brittle, conductor/insulator), rusting and prevention, difference between metals and non-metals, NCERT “Let Us Enhance Our Learning” questions, and daily life applications.
Fig. 4.1: Ironsmith at Work

Children observe an ironsmith heating iron till red hot and beating it into flat tools; this shows malleability of metals.

4.1 Properties of Materials

Malleability

  • Metals like copper, aluminium, and iron are hard, lustrous, and malleable—they can be beaten into thin sheets without breaking. Thin foils of silver and aluminium (for sweets and wrapping food) are examples of malleability.
  • Non-metals like coal and sulfur are brittle—they break into pieces when hammered instead of flattening. Wood is neither malleable nor brittle in this sense.

Ductility

  • Ductility means the ability of a material to be drawn into thin wires. Copper and aluminium wires used in electrical wiring and strings in instruments like veena, sitar, violin are ductile metals.
  • Gold is extremely ductile; a very small mass can be drawn into a very long wire. Coal and sulfur cannot be drawn into wires, so they are not ductile.

Sonority

  • When a metal spoon or coin is dropped, it makes a clear ringing sound. This property of producing a ringing sound is called sonority; metals are sonorous.
  • Coal and wood give dull sounds on dropping; they are not sonorous. School bells, temple bells, and ghungroos use metals for this reason.

Conduction of Heat and Electricity

  • Metals like copper and aluminium are good conductors of heat; they quickly become hot when their lower parts are placed in hot water. That is why cooking vessels are metal, while handles are wood or plastic (poor conductors).
  • Metals are good conductors of electricity, so wires for circuits are made of metals like copper and aluminium. Materials like wood, coal, eraser, plastic, and nylon rope are poor conductors and do not let the bulb glow in a tester.

4.2 Effect of Air and Water on Metals: Rusting and Corrosion

  • Iron objects develop brown deposits when exposed to moist air (air + water). Experiments with nails in bottles A (dry air), B (only boiled water + oil), and C (air + water) show that rust forms only when both air and water are present.
  • The brown deposit on iron is called rust, and the process is called rusting. Gradual damage of metal surfaces due to air, water, and other substances is called corrosion (like green coating on copper and black coating on silver).
  • Rusting causes huge economic loss; prevention methods include painting, oiling, greasing, and coating iron with zinc (galvanisation, studied in higher grades).
Bottles A, B, C Setup

Dry air (A) and only water (B) do not cause rust; moist air (C) causes rust on iron nails, proving that both air and water are needed.

4.3 Effect of Air and Water on Other Metals

  • Burning magnesium ribbon in air produces a dazzling white flame and forms magnesium oxide, a white powder. Its solution in water turns red litmus blue, showing that metal oxides are generally basic in nature.
  • Reactive metals like sodium react vigorously with oxygen and water, releasing a lot of heat. Sodium is stored in kerosene to prevent dangerous reaction with moisture and air.

4.4 Substances that Behave Differently from Metals: Non-metals

  • When sulfur is burnt in air, sulfur dioxide gas is formed. Its solution in water turns blue litmus red, showing that oxides of non-metals are generally acidic.
  • Sulfur does not react with water the way metals do. Non-metals like sulfur and phosphorus are usually dull, soft, not malleable, not ductile, non-sonorous, and poor conductors of heat and electricity.
  • Phosphorus is stored in water because it catches fire in air easily. Non-metals like oxygen, hydrogen, nitrogen, and carbon are elements and are different from materials like plastic or glass (which are not elements).

4.5 Are Non-metals Essential in Everyday Life?

  • Oxygen is a non-metal essential for respiration; without it, living beings cannot survive. It is also used in medical care and industries.
  • Carbon is a basic building block of life; it is present in proteins, fats, and carbohydrates. Nitrogen is important for plant growth and is used in fertilisers.
  • Chlorine is used in water purification, and iodine solution is applied on wounds as an antiseptic. Non-metals play crucial roles in health, agriculture, and hygiene.

In a Nutshell (Textbook Style Points)

  • Metals are generally lustrous, malleable, ductile, sonorous, and good conductors of heat and electricity; non-metals are usually non-lustrous, brittle (if solid), and poor conductors.
  • Metals form basic oxides with oxygen; non-metals form acidic oxides. Metals can corrode; rusting of iron is a special case of corrosion in moist air.
  • Metals and non-metals are elements and act as building blocks of matter. Both categories are essential in everyday life and modern technology.

Metals in Indian History and Technology

Use of iron tools greatly improved agriculture and tools in ancient India. The famous Iron Pillar of Delhi shows advanced metallurgical skills that resisted rusting for more than a thousand years.

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