CBSE Class 7 Science Revision Notes Chapter 4: The World of Metals and Non-metals

Metals and non-metals can be distinguished through properties such as lustre, hardness, malleability, ductility, sonority and conductivity.

Their reactions with air, water and oxygen also help us understand why they are used for different purposes.

Metals are used in cooking vessels, tools, electric wires, machines, jewellery, buildings and vehicles. Non-metals are equally important because oxygen supports respiration, nitrogen helps plants grow, chlorine is used in water purification and iodine is used as an antiseptic.

These CBSE Class 7 Science Revision Notes Chapter 4 follow the current 2026–27 chapter. They explain the physical properties of metals and non-metals, conduction of heat and electricity, rusting and corrosion, reactions with oxygen and water, and the uses of different elements in daily life.

Key Takeaways

• Malleability: Most metals can be beaten into thin sheets without breaking.
• Ductility: Metals such as copper, aluminium and gold can be drawn into wires.
• Rusting: Iron develops rust only when both air and water are present.
• Oxides: Metal oxides are generally basic, while non-metal oxides are generally acidic.

Access Class 7 Science Chapter 4 The World of Metals and Non-metals Notes in 30 Minutes

Use the first 10 minutes to revise lustre, hardness, malleability, ductility and sonority. Spend the next 10 minutes on heat conduction, electrical conduction, rusting and corrosion.

Use the final 10 minutes to revise reactions with oxygen and water, metal and non-metal oxides, and the uses of important metals and non-metals.

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Metals and Non-metals in Class 7 Science Chapter 4 Notes

Metals and non-metals are two broad categories of elements. An element is a substance that cannot be broken into simpler substances by ordinary chemical methods.

Iron, copper, aluminium, gold, silver, sodium and mercury are examples of metals. Oxygen, nitrogen, carbon, sulfur, hydrogen, chlorine, iodine and phosphorus are examples of non-metals.

Materials such as wood, plastic, paper, rubber and glass should not automatically be called non-metals. They are materials made from different substances, while metals and non-metals are categories used mainly for elements.

Physical Properties of Metals and Non-metals

Metals and non-metals can be identified by observing their appearance, hardness and behaviour when they are hammered, stretched, dropped or included in a circuit. These properties also explain why particular materials are selected for tools, utensils, wires and musical instruments.

Lustre

The shiny appearance shown by a metal is called metallic lustre. Fresh or cleaned surfaces of copper, aluminium, iron, gold and silver usually appear shiny.

Most non-metals have a dull appearance. Coal and sulfur generally do not show metallic lustre.

Hardness

Most metals are hard and resist pressure or scratching. Iron, copper and aluminium are harder than many common non-metallic materials.

However, all metals are not hard. Sodium and potassium are soft enough to be cut with a knife, while mercury is a metal that remains liquid at room temperature.

Malleability in The World of Metals and Non-metals Notes

Malleability is the property by which a material can be beaten into thin sheets without breaking. Most metals possess this property, which allows craftspersons to shape iron, copper and aluminium into useful objects.

When copper, aluminium or iron is beaten with a hammer, it becomes flatter. This is why metals can be used to make aluminium foil, silver foil, utensils, vehicle bodies and roofing sheets.

Gold and silver are among the most malleable metals. They can be shaped into extremely thin sheets without breaking.

Brittleness

A brittle substance breaks into smaller pieces when struck with a hammer. Coal and sulfur show brittleness because they break instead of becoming flat.

Wood behaves differently. It may neither flatten into a sheet nor break into small pieces under the same conditions, so it is neither malleable nor brittle in this comparison.

Ductility

Ductility is the property by which a material can be drawn into wires. This property is mainly shown by metals such as copper, aluminium, gold, silver and iron.

Metal wires are used in electrical fittings, jewellery, tea strainers, musical instruments, cranes and suspension bridges. Copper and aluminium are widely used for electrical wiring, while metal strings are used in instruments such as the veena, sitar, violin and guitar.

Gold is highly ductile. One gram of gold can be drawn into a wire about two kilometres long.

Steel ropes are made from many strong metal wires twisted together. These ropes can support heavy loads, so they are used in suspension bridges, cranes and lifts.

Sonority of Metals

Sonority is the property of producing a ringing sound when struck or dropped. Metals are generally sonorous, while coal, wood and many non-metallic materials produce dull sounds.

A metal spoon, coin, bell or plate produces a clear ringing sound. This property explains why metals are used in school bells, ghungroos, cymbals and several musical instruments.

A hard material is not always sonorous. Sonority is a characteristic property associated mainly with metals.

Conductors of Heat and Electricity

Metals generally allow heat and electric current to pass through them easily. This makes them useful in cooking vessels, electric wires, plugs, machines and electrical devices.

At the same time, poor conductors are also important. They are used for handles and coverings to protect people from heat and electric shock.

Conduction of Heat

The transfer of heat from one part of a material to another is called conduction. A material that transfers heat easily is called a good conductor of heat.

When a metal spoon and a wooden spoon are placed in hot water, the upper end of the metal spoon becomes hotter. The wooden spoon remains comparatively cooler because wood transfers heat poorly.

This explains why cooking vessels are usually made of metal. Their handles are often made of wood, plastic or another poor conductor so that they can be held safely.

Uses Based on Heat Conduction

Metals are used in frying pans, pressure cookers, kettles, iron plates and cooking utensils. Wood and plastic are used in handles because they slow down the transfer of heat to the hand.

Conduction of Electricity

Materials that allow electric current to pass through them easily are called good conductors of electricity. Most metals are good electrical conductors.

A tester circuit can be used to check whether a material conducts electricity. If the test material is placed between two free wire ends and the bulb glows, the material allows current to pass.

Aluminium foil, iron nails and copper wires make the bulb glow because they are conductors. Sulfur, dry wood, rubber, nylon rope and stone do not make the bulb glow in this activity because they are poor conductors.

Why Are Electrician’s Tools Covered?

The metal part of a screwdriver conducts electricity. Its handle is covered with plastic because plastic is a poor conductor and helps reduce the risk of electric shock.

Electricians also use rubber gloves and shoes for protection. Rubber does not allow electric current to pass through it easily.

Rusting and Corrosion in Chapter 4 Science Revision Notes

Metals can slowly become damaged when they remain exposed to air, water or other substances. Iron commonly develops a brown deposit known as rust.

What Is Rusting?

The process through which iron develops a brown coating in the presence of air and water is called rusting. The brown substance formed on the surface is called rust.

Both air and water are required for rusting. This can be shown with an experiment using three bottles.

Bottle A: Iron Nail in Dry Air

An iron nail is placed in a closed bottle with silica gel. Silica gel absorbs moisture and keeps the air dry.

Air is present, but water is absent. The nail does not rust.

Bottle B: Iron Nail in Water without Air

Another nail is placed in boiled and cooled water. Boiling removes dissolved air, while a layer of oil prevents air from entering the water again.

Water is present, but air is nearly absent. The nail does not rust.

Bottle C: Iron Nail with Air and Water

The third nail is partly dipped in water in an open bottle. It remains in contact with both water and air.

The nail develops a brown deposit. This proves that both air and water are needed for rusting.

What Is Corrosion?

Corrosion is the gradual deterioration of a metal surface due to air, water or other substances. Rusting is a type of corrosion that specifically affects iron.

Copper may develop a green coating, while silver may form a black coating. These are other examples of corrosion.

Prevention of Rusting

Rusting weakens iron gates, tools, machines, bridges, vehicles and pipes. It also causes large financial losses because damaged structures must be repaired or replaced.

Rusting can be reduced by preventing air and water from reaching the iron surface. Common methods include painting, oiling, greasing and galvanisation.

Painting

Paint forms a protective layer over iron. It prevents moisture and air from directly touching the metal.

Oiling and Greasing

Oil and grease form a thin protective film. They are commonly applied to tools, chains, hinges and machine parts.

Galvanisation

Galvanisation is the process of coating iron with a thin layer of zinc. The zinc layer protects the iron below from direct contact with air and water.

Iron Pillar of Delhi

The Iron Pillar of Delhi was made more than 1,600 years ago. It is about eight metres high and weighs more than 6,000 kilograms.

Despite long exposure to rainfall, wind and changing weather, it has developed very little rust. This shows the advanced knowledge and metalworking skills present in ancient India.

Reaction of Metals with Oxygen and Water

Metals react differently with air and water. Some react slowly, while metals such as sodium react very quickly.

The nature of the products formed also helps us compare metals and non-metals.

Burning Magnesium

Magnesium ribbon burns in air with a dazzling white flame. It forms a white powder called magnesium oxide.

Before burning, the ribbon is cleaned with sandpaper. This removes the coating formed on its surface and allows the metal to burn properly.

Magnesium + Oxygen → Magnesium oxide

When magnesium oxide is mixed with warm water, the solution turns red litmus paper blue. This shows that magnesium oxide is basic in nature.

Metal oxides are generally basic.

Sodium and Water

Sodium is a highly reactive metal. It reacts vigorously with air and water and releases a large amount of heat.

For this reason, sodium is stored in kerosene. Kerosene prevents it from coming into direct contact with air and moisture.

Reaction of Non-metals with Oxygen and Water

Non-metals generally behave differently from metals when they react with oxygen and water. Sulfur is used in the chapter to demonstrate these differences.

Burning Sulfur

Sulfur burns in oxygen and produces sulfur dioxide gas. This experiment must be performed by a teacher in a well-ventilated area because the gas can be harmful if inhaled.

Sulfur + Oxygen → Sulfur dioxide

When sulfur dioxide dissolves in water, it forms an acidic solution. The solution turns blue litmus paper red.

Non-metal oxides are generally acidic.

Sulfur and Water

Sulfur does not show a noticeable reaction when placed in water. This is different from highly reactive metals such as sodium.

Phosphorus is another non-metal with special storage requirements. It can catch fire when exposed to air, so it is stored under water.

Metal Oxides and Non-metal Oxides

Metals and non-metals form different types of oxides when they react with oxygen. Testing their solutions with litmus helps identify whether the oxides are acidic or basic.

Magnesium oxide is a metal oxide and shows basic properties. Sulfur dioxide is formed from a non-metal and gives an acidic solution in water.

Metals and Non-metals Comparison

The following table summarises the general differences. These are broad patterns, so exceptions may exist.

Important Exceptions

Sodium and potassium are soft metals, while mercury is liquid at room temperature. Therefore, properties of metals and non-metals should generally be described using words such as “usually” or “generally.”

Uses of Metals and Non-metals

The properties of metals and non-metals determine their uses. Strength, malleability, conductivity, ductility and chemical behaviour all influence where a substance is used.

Uses of Metals

Iron

Iron is strong and widely available. It is used in agricultural tools, machines, bridges, buildings, vehicles and construction materials.

Copper

Copper conducts heat and electricity efficiently. It is used in electrical wiring, cooking vessels, decorative objects and electrical devices.

Aluminium

Aluminium is light, malleable and a good conductor. It is used in food wrapping foil, cooking vessels, cans, aircraft parts and electrical wires.

Gold and Silver

Gold and silver are lustrous, malleable and ductile. These properties allow them to be shaped into detailed jewellery and fine wires.

Special Metals

Some metals are required for advanced technology. Titanium is used in aerospace applications, while zirconium has uses in atomic energy.

Uses of Non-metals

Oxygen

Oxygen is essential for respiration. Humans, animals and many other organisms depend on it for survival.

Carbon

Carbon is an important part of living organisms. It is present in proteins, fats, carbohydrates, fuels and many other substances.

Nitrogen

Nitrogen is needed for plant growth. It is used in fertilisers and in the manufacture of several chemicals.

Chlorine

Chlorine is used in water purification. It helps control harmful microorganisms in water.

Iodine

Iodine solution is used as an antiseptic on minor wounds. The body also requires iodine in small quantities.

Iron and the Progress of Civilisation

Early civilisations used metals such as copper and gold for utensils, jewellery and tools. Iron became widely used later because extracting and working with it required more advanced techniques.

Iron tools were stronger than many earlier tools. Iron ploughs, axes and other farming implements helped improve agriculture, construction and craft production.

India also has a rich tradition of metal art. Dhokra, Bidriware, Pembarthi and Kamrupi are examples of well-known metal crafts that connect scientific knowledge with art, history and culture.

Metals, Recycling and Sustainability

Metals are valuable natural resources. Mining and processing them require energy and may affect land, water and ecosystems.

Recycling iron, aluminium and other metals reduces the need for fresh mining. It also saves energy, reduces waste and allows useful materials to be recovered from old objects.

Smartphones and other electronic devices contain many metals and non-metals. Recovering these materials from electronic waste is an important part of responsible resource use.

Class 7 Science Chapter 4 Summary Notes

Important Terms from The World of Metals and Non-metals

Metal: An element that generally shows lustre, malleability, ductility and good conductivity.

Non-metal: An element that generally does not show typical metallic properties.

Metallic lustre: The shiny appearance of a metal surface.

Malleability: The ability of a material to be beaten into thin sheets.

Brittleness: The tendency of a material to break when struck.

Ductility: The ability of a material to be drawn into wires.

Sonority: The property of producing a ringing sound.

Conduction: The transfer of heat or electric current through a material.

Rusting: The formation of rust on iron in the presence of air and water.

Corrosion: The gradual damage of a metal surface due to surrounding substances.

Galvanisation: The process of coating iron with zinc to prevent rusting.

Metal oxide: An oxide formed when a metal reacts with oxygen.

Non-metal oxide: An oxide formed when a non-metal reacts with oxygen.

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