Chapter Notes

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.

• 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.

Conduction of heat

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

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.

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.

Effect of Air and Water on Metals: Iron

Iron objects develop brown deposits (rust) when left in the open for a few days.

• Bottle A: Iron nail with silica gel (dry air) - No rust.
• Bottle B: Iron nail in boiled, cooled water with oil layer (water, no air) - No rust.
• Bottle C: Iron nail partially dipped in water (air and water) - Rust.

Rust is the brown deposit formed on iron objects. Rusting is the process of rust formation. Moist air is responsible for rusting.

Other metals also exhibit discolouration. Copper forms a green coating, and silver forms a black coating. Corrosion is the gradual deterioration of metal surfaces caused by air, water, or other substances.

Rusting is a serious problem, costing enormous amounts of money to replace damaged iron structures. Rusting can be prevented by painting, oiling, greasing, and galvanisation (applying a protective layer of zinc metal).

The wonder of ancient Indian metallurgy!

The Iron Pillar of Delhi, made over 1600 years ago, has very little rust due to advanced metal technology.

Effect of Air and Water on Other Metals

Magnesium ribbon burns with a dazzling white flame and changes into a white powder (magnesium oxide). Magnesium oxide is formed due to the reaction between magnesium and oxygen in the air.

Adding water to magnesium oxide forms a solution that turns red litmus paper blue, indicating it is basic in nature (Fig 4.6). Generally, oxides of metals are basic in nature.

Sodium is stored in kerosene because it reacts vigorously with oxygen and water, generating heat. Kerosene prevents its exposure to moisture and air.

Substances that Behave Differently from Metals in Air and Water

Burning sulfur in air (oxygen) forms sulfur dioxide gas. Dissolving sulfur dioxide in water forms sulfurous acid. The solution is acidic.

Sulfur does not react when placed in water.

Substances like sulfur and phosphorus behave differently with air and water than metals. Phosphorus is stored in water as it catches fire when exposed to atmospheric air.

Non-metals are usually soft and dull in appearance, neither malleable nor ductile, not sonorous, and poor conductors of heat and electricity. Their oxides are acidic in nature.

Examples of non-metals are oxygen, hydrogen, nitrogen, and carbon.

Metals and non-metals are sub-categories of elements. An element is a substance that cannot be broken down into simpler substances.

Currently, 118 elements are known.

Are Non-metals Essential in Everyday Life?

Non-metals are important in our lives.

• Oxygen is essential for breathing.
• Carbon is the building block of all life forms (proteins, fats, carbohydrates).
• Nitrogen is used in fertilizers.
• Chlorine is used in water purification.
• Iodine is used as an antiseptic.

Science and Society

Metals and their alloys are important for daily use as utensils and tools and for modern technologies. Special metals are used in atomic energy (zirconium) and aerospace (titanium). In India, many metals, especially iron and aluminum, are recycled.