Chapter 4: The World of Metals and Non-metals — Class 7 Science
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Summary, key terms, important questions and a practice quiz with AI diagnosis for each.
Chapter 4: The World of Metals and Non-metals
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Which property allows metals to be beaten into thin sheets?
Summary
This chapter distinguishes metals from non-metals through their physical and chemical properties. Metals such as copper, aluminium, and iron are generally lustrous (metallic lustre), hard, malleable (can be beaten into thin sheets), ductile (can be drawn into wires), sonorous (produce a ringing sound), and good conductors of heat and electricity. There are exceptions: sodium and potassium are soft enough to cut with a knife, mercury is a liquid at room temperature, and gold and silver are the most malleable and ductile. Non-metals such as coal, sulfur, and phosphorus are usually dull, soft or brittle, neither malleable nor ductile, not sonorous, and poor conductors of heat and electricity. The chapter examines the effect of air and water on metals: iron develops brown deposits called rust only when both water and air (moist air) are present, a process called rusting; the slow deterioration of metal surfaces in general is called corrosion. Burning magnesium ribbon forms white magnesium oxide, whose solution turns red litmus blue, showing metal oxides are basic. Burning sulfur forms sulfur dioxide, which dissolves in water to give sulfurous acid, showing non-metal oxides are acidic. Metals and non-metals are sub-categories of elements — substances that cannot be broken into simpler ones, of which 118 are presently known. Non-metals are essential to life too: we breathe oxygen, carbon is the building block of living things, nitrogen helps make fertilisers, chlorine purifies water, and iodine acts as an antiseptic.
Properties of metals and non-metalsMalleability, ductility, and sonorityConduction of heat and electricityRusting and corrosionAcidic and basic nature of oxides
Key terms
Metallic lustre
The shine shown by the surface of metals such as copper, aluminium, and iron.
Malleability
The property by which a material can be beaten into thin sheets; gold and silver are the most malleable.
Ductility
The property by which a material can be drawn into wires; mainly possessed by metals.
Sonority
The property of metals by which they produce a ringing sound when struck.
Rusting
The formation of a brown deposit (rust) on iron when it is exposed to both air and water (moist air).
Corrosion
The gradual deterioration of metal surfaces caused by air, water, or other substances.
Element
A substance that cannot be broken down into simpler substances; metals and non-metals are sub-categories of elements.
Important questions
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Metallic lustre
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The shine shown by the surface of metals such as copper, aluminium, and iron.
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Practice quiz · The World of Metals and Non-metals
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