Notes Chapter 4 Class 7 Science Curiosity NCERT

The World of Metals and Non-metals

1. Properties of Materials

Malleability

• Definition: Ability to be beaten into thin sheets.
• Metals: Copper, aluminium, iron are malleable (e.g., aluminium foil, silver foil).
• Non-metals: Coal, sulfur are brittle; wood is neither malleable nor brittle.
• Exceptions: Sodium, potassium (soft metals); mercury (liquid metal).

Ductility

• Definition: Ability to be drawn into wires.
• Metals: Copper, aluminium, gold (e.g., electrical wires, jewellery).
• Non-metals: Coal, sulfur are not ductile.
• Fact: 1 gram of gold can make a 2 km wire.

Sonority

• Definition: Ability to produce a ringing sound when struck.
• Metals: Sonorous (e.g., bells, ghungroos).
• Non-metals: Non-sonorous (dull sound).

Conduction of Heat

• Metals: Good conductors (e.g., cooking vessels).
• Non-metals: Poor conductors (e.g., wooden handles).

Conduction of Electricity

• Metals: Good conductors (e.g., copper wires).
• Non-metals: Poor conductors (e.g., rubber gloves, plastic handles).

2 .Effect of Air and Water on Metals: Iron

• Rusting: Brown deposit (rust) forms on iron when exposed to both air and water.
• Corrosion: Gradual deterioration of metals (e.g., green coating on copper, black on silver).
• Prevention: Painting, oiling, greasing, galvanisation (zinc coating).
• Fact: Iron Pillar of Delhi (1600+ years) resists rust due to ancient metallurgy.

3 Effect of Air and Water on Other Metals

• Magnesium: Burns with white flame, forms magnesium oxide (basic).
• Sodium: Stored in kerosene; reacts vigorously with air and water.

4.Non-metals

• Properties: Soft, non-lustrous, brittle, non-ductile, non-sonorous, poor conductors.
• Examples: Sulfur, phosphorus, oxygen, carbon, nitrogen.
• Sulfur: Burns to form sulfur dioxide (acidic); no reaction with water.
• Phosphorus: Stored in water to prevent burning in air.

 5. Importance of Non-metals

• Oxygen: Essential for respiration.
• Carbon: Building block of life (proteins, fats, carbohydrates).
• Nitrogen: Used in fertilisers for plant growth.
• Chlorine: Water purification.
• Iodine: Antiseptic for wounds.

Key Points

• Metals: Lustrous, hard, malleable, ductile, sonorous, good conductors; form basic oxides.
• Non-metals: Non-lustrous, soft, brittle, non-ductile, non-sonorous, poor conductors; form acidic oxides.
• Elements: 118 known; metals and non-metals are sub-categories.
• Applications: Metals in utensils, tools, technology; non-metals in life processes, industries.