The World of Metals and Non-metalsClass 7 Science Notes

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Section 1 of 4

The World of Metals and Non-metals

Yashwant and Anandi, while visiting local ironsmiths, learned about items made of iron and how they are shaped. This leads to exploring the properties of materials, specifically metals and non-metals.

Properties of Materials

Malleability

Malleability is the property of a material that allows it to be beaten into thin sheets.

Activity 4.1 explores the malleability of different materials. Copper, aluminum, and iron can be flattened by hammering, while coal and sulfur break into pieces. Wood doesn't flatten or break.
  • Metals like copper, aluminum, and iron are lustrous and hard.
  • The lustre shown by metals is known as metallic lustre.
  • Coal, sulfur, and wood are non-lustrous and not as hard as metals.
  • Some metals, like sodium and potassium, are soft and can be cut with a knife.
  • Mercury is a metal that is liquid at room temperature.

Copper, iron, and aluminum become flat when beaten. Coal and sulfur break into pieces; these are said to be brittle. Wood is neither malleable nor brittle. Gold and silver are the most malleable metals.

Holistic Lens: The impact of iron on the progress of civilisation of India

The use of iron in India significantly contributed to the progress of civilization. Iron tools, like ploughs, were stronger and more effective than previous tools made of other materials. Copper was likely discovered before iron.

Ductility

Ductility is the property of a material that allows it to be drawn into wires.

Metal wires are used in electrical fittings, ornaments (bangles, necklaces, earrings), and stringed musical instruments (veena, sitar, violin, guitar). Ductility is mainly possessed by metals. Coal and sulfur are not ductile.

Sonority

Sonority is the property of a material that allows it to produce a ringing sound when struck. Metals are said to be sonorous in nature.

Activity 4.2 demonstrates sonority. A metal spoon or coin produces a ringing sound when dropped on the floor, while coal or wood produce dull sounds.

Conduction of heat

Conduction is the transfer of heat from one point to another in a material. Materials that transfer heat are called conductors.

Example
In the kitchen, cooking vessels are made of metals because metals are good conductors of heat.
Warning
This activity must be performed under the supervision of your teacher or an adult. Be careful while handling hot water.
Example
In the experiment with metal and wooden spoons immersed in hot water (Fig 4.3), the metal spoon gets hotter than the wooden spoon, indicating that metals are good conductors of heat, while wood is a poor conductor of heat.

Handles of cooking vessels are made of wood or other materials that do not conduct heat.

Conduction of electricity

Good conductors of electricity are materials that allow electricity to flow through them easily. Poor conductors of electricity do not allow electricity to pass through them easily.

Activity 4.4 demonstrates electrical conductivity. Aluminum, iron, and copper make a bulb glow, while sulfur, coal, wood, stone, eraser, and nylon rope do not.

Plastic coverings on screwdrivers and rubber gloves protect electricians from electric shock because these materials are poor conductors of electricity.

Metals are generally hard, lustrous, malleable, ductile, and good conductors of heat and electricity.