NCERT Curiosity · Class 7 · Science
The World of Metals and Non-metals
An ironsmith heats a block red-hot and hammers it into an axe. Anandi wonders: can we do this with every metal?
Key idea
Properties of Metals
1
Lustre
A shiny surface — copper, aluminium, iron.
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2
Malleability
Can be beaten into thin sheets — gold and silver most of all.
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3
Ductility
Can be drawn into wires — 1 g of gold stretches into 2 km of wire.
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4
Sonority
Produces a ringing sound when struck — think bells.
Key idea
Conduction of Heat and Electricity
1
Heat
Metals conduct heat well — that's why cooking vessels are metal, but their handles are wood (a poor conductor).
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2
Electricity
Aluminium, iron, and copper let a tester bulb glow. That's why electricians wear rubber gloves and use plastic-handled tools.
Key idea
Metals That Break the Rules
1
Soft metals
Sodium and potassium are soft enough to cut with a knife.
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2
A liquid metal
Mercury is a metal that stays liquid at room temperature.
Key idea
What Causes Iron to Rust?
An experiment with three sealed bottles shows the answer clearly.
Dry air onlyNail + silica gel, sealed. No rust forms.
Water onlyNail fully underwater, sealed with an oil layer. No rust forms.
Air + waterNail half in water, open to air. Rust forms.
Key idea
Rust, Corrosion, and Prevention
1
Rust and corrosion
Rust is the brown deposit on iron. Corrosion is the broader, gradual wearing away of any metal surface — like the green coating on copper or the black coating on silver.
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2
Preventing rust
Painting, oiling, greasing, or galvanisation (coating iron with zinc) all keep air and water away from the metal.
Key idea
Burning Magnesium
Burning magnesium ribbon produces a dazzling white flame and a white powder — magnesium oxide.
Basic in natureMagnesium oxide dissolved in water turns red litmus blue — metal oxides are generally basic.
Key idea
Sodium: Stored in Kerosene
Why kerosene?. Sodium reacts vigorously with both oxygen and water, releasing a great deal of heat — so it's kept away from air and water by storing it under kerosene.
Key idea
Burning Sulfur
Burning sulfur produces sulfur dioxide gas, which dissolves in water to turn blue litmus red.
Acidic in natureNon-metal oxides, unlike metal oxides, are acidic. Sulfur itself does not react with water at all.
Key idea
Phosphorus: Stored in Water
Why water?. Phosphorus catches fire the moment it's exposed to air, so it's stored underwater to keep air away from it.
Key idea
Metals vs Non-metals
Property | Metals | Non-metals
Malleability / DuctilityYes — No — often brittle
SonorityRing when struck — No ringing sound
Conduction (heat, electricity)Good — Poor
Nature of oxideBasic — Acidic
Key idea
Non-metals Are Essential Too
1
Oxygen
Essential for breathing and survival.
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2
Carbon
The building block of all life forms.
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3
Nitrogen
Used in fertilisers, essential for plant growth.
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4
Chlorine & Iodine
Chlorine purifies water; iodine is an antiseptic.
Chapter · Key terms to remember
Key Terms
Metallic lustre
The shiny appearance of metals.
Malleability
Being beaten into thin sheets.
Ductility
Being drawn into wires.
Chapter · Key terms to remember
More Key Terms
Sonority
Producing a ringing sound when struck.
Rust / Rusting
The brown deposit on iron / how it forms.
Corrosion
Gradual wearing away of a metal surface.
Chapter · Key terms to remember
More Key Terms
Galvanisation
Coating iron with zinc to prevent rusting.
Alloy
A mixture of metals, or metal with non-metal.
Questions for your notebook
Write these down, then discuss
1Which metal is commonly used for food packaging, since it's cheap and its thin sheets fold easily into any shape? (i) Aluminium (ii) Copper (iii) Iron (iv) Gold
2Which metal catches fire when it comes into contact with water? (i) Copper (ii) Aluminium (iii) Zinc (iv) Sodium
3Why are only a few metals suitable for making jewellery?
Project as-is — students copy the questions, then the class discusses answers together.