CBSE Class 8 Science Chapter 4 Revision Notes

Chapter 4: Materials: Metals And Non-Metals Revision Notes

Everything in our environment is classified as metals or non-metals with distinct properties. Metals are robust and long-lasting. As a result, metals are used in practically every industry.

• Metal examples: Iron, aluminium, copper, calcium, magnesium

• Non-metal examples: Coal, sulphur, wood, plastic, oxygen, phosphorous

PHYSICAL CHARACTERISTICS OF METALS AND NON-METALS

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(i) Malleable:

• Metals can be moulded into thin, flat sheets with ease. The term for this property of metals is malleability.
• Non-metals are non-malleable.

(ii) Thermal conductors:

• Metals are excellent heat conductors.
• Cooking utensils, irons, heaters, and other similar items are all made of metals that are good heat conductors.
• But the handles of these items are made of non-metals that do not conduct heat (poor conductors).

(iii) Ductility:

• Metals are simple to form into wires. The term for this feature of metals is ductility. Copper and aluminium wires are good conductors of electricity.
• Non-metals are non-ductile and do not conduct electricity.

(iv) Sonorous:

• When metals are struck with hard items, they generate a sonorous ringing sound.
• Non-metals aren’t particularly sonorous. When they are hit, they make no sound.

(v) Some metals are hard and can be polished to a gleaming finish.

(vi) Except for ductile carbon fibres, non-metals are non-lustrous.

CHEMICAL PROPERTIES OF METALS AND NON-METALS

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(i) Reaction with oxygen:

• Metal oxides are basic in nature and are formed when metals react with oxygen (rust).
• Non-metallic oxides, which are acidic in nature, are formed when non-metals react with oxygen.

(ii) Reaction with water:

• Metal hydroxides and hydrogen gas are produced when some metals react with water.
• Non-metals, in general, do not react with water.

(iii) Reactions with acids:

• When metals react with acids, hydrogen gas is formed.
• Non-metals, on the whole, do not react with acids.

(iv) Reactions with bases:

• Some metals create hydrogen gas when they react with bases.
• In aqueous solutions, more reactive metals displace less reactive metals from their compounds (displacement reactions).

USES OF METALS AND NON-METALS

Metals and non-metals are commonly used in daily life.

• Metals, for example, are used in the manufacture of machinery, automobiles, aeroplanes, buildings, railroads, satellites, gadgets, cooking utensils, and water boilers, among other things.
• Non-metals are used in fertilizers, water purification processes, antiseptics, crackers, etc.

Source: Class 8 Science book Chapter 4. Materials Metals & Non-Metals (ncerthelp.com)

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