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The World of Metals and Non-metals – Class 7 Science notes, important questions and MCQs

NCERT Class 7 Science, chapter 4. Notes, key terms, important questions with answers and MCQs.

Chapter overview

Metals are usually shiny, hard, malleable, ductile and good conductors; non-metals are mostly dull, brittle and poor conductors. Their reactions with oxygen, water and acids differ.

Physical properties

Metals: lustre, malleability (sheets), ductility (wires), sonority (ringing sound), conductivity.
Non-metals: dull, brittle, non-sonorous, poor conductors (except graphite).
Exceptions: mercury is a liquid metal; sodium is soft; diamond (non-metal) is the hardest substance.

Chemical properties

Metal + oxygen → metal oxide (basic): magnesium burns with a bright white flame.
Non-metal + oxygen → non-metal oxide (acidic): sulphur dioxide.
Rusting: iron + oxygen + water → rust; prevented by painting, oiling, galvanising.
Sodium reacts violently with water, so it is stored in kerosene.

Key terms

Malleability: ability to be beaten into thin sheets
Sonorous: producing a ringing sound when struck
Rusting: formation of iron oxide on iron in moist air

Formulas

2Mg + O₂ → 2MgO
S + O₂ → SO₂

Important questions with answers

Why are metals used to make bells?2 marks

Metals are sonorous: they produce a ringing sound when struck.

What is rusting? Give two ways to prevent it.3 marks

Rusting is the formation of a brown flaky substance (iron oxide) on iron in the presence of air and water. Prevent it by painting or oiling, or by galvanising (coating with zinc).

Compare metals and non-metals on five properties, and explain what happens when metal oxides and non-metal oxides are dissolved in water.5 marks

Metals are lustrous, malleable, ductile, sonorous and good conductors of heat and electricity; non-metals are usually dull, brittle, not sonorous and poor conductors (graphite is an exception). Metal oxides dissolve to form basic solutions (magnesium oxide in water turns red litmus blue). Non-metal oxides dissolve to form acidic solutions (sulphur dioxide in water turns blue litmus red).

Quick revision

Metals form basic oxides.
Non-metals form acidic oxides.
Rust needs both air and water.

Exam tips

Metal oxides turn red litmus blue; non-metal oxides turn blue litmus red.
Aluminium foil and copper wires show malleability and ductility.

Practice MCQs

Which is a liquid metal?
1. sodium
2. mercury
3. iron
4. bromine
Show answer
Answer: (b) mercury. Bromine is a liquid non-metal.
Metals that can be drawn into wires are
1. malleable
2. brittle
3. sonorous
4. ductile
Show answer
Answer: (d) ductile. Ductile.
Magnesium oxide in water turns red litmus
1. blue
2. red
3. green
4. colourless
Show answer
Answer: (a) blue. Basic oxide.
Which non-metal conducts electricity?
1. graphite
2. sulphur
3. oxygen
4. iodine
Show answer
Answer: (a) graphite. Graphite.
Which non-metal is a good conductor of electricity
1. sulphur
2. graphite
3. phosphorus
4. oxygen
Show answer
Answer: (b) graphite. Form of carbon.
Iron nails kept in dry air and in boiled water with oil on top do not rust because
1. both air and water are needed for rusting
2. iron is pure
3. oil reacts with iron
4. boiling adds oxygen
Show answer
Answer: (a) both air and water are needed for rusting. One of the two is missing.
Why is sodium stored in kerosene?
1. it is very hard
2. it reacts vigorously with air and water
3. it is costly
4. it smells
Show answer
Answer: (b) it reacts vigorously with air and water. To prevent fire.
When a copper vessel is left in moist air, it gets a
1. red coating
2. silver coating
3. black coating only
4. green coating
Show answer
Answer: (d) green coating. Basic copper carbonate.

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Written by Kundali IQ from standard, well-established facts to help with revision. This is not an official NCERT publication; always read your textbook too.