The World of Metals and Non-metals | CBSE Class 7 Science Notes

This note covers metals and non-metals, their properties and everyday uses, tests with heat and electricity, changes in air and water, the formation and prevention of brown deposits on iron, and the products formed when magnesium and sulfur burn.

What are metals and non-metals, and how can we recognise them?

What is an element?

An element is a substance that cannot be broken down into simpler substances. Metals and non-metals are two sub-categories of elements. Elements are the basic building blocks of matter, and 118 elements are known.

Some elements occur naturally. Others are made artificially in laboratories and do not exist in nature. Metals, such as copper, aluminium and iron, are generally hard, shiny, capable of being shaped into sheets and wires, and good at carrying heat and electricity.

Non-metals include sulfur, phosphorus, oxygen, hydrogen, nitrogen and carbon. Substances such as sulfur and phosphorus are usually soft and dull. Non-metals are generally poor conductors, meaning that heat and electricity do not pass through them easily.

Note: Plastic, glass, wood, rubber and paper are not classified as metals or non-metals because they are not elements. A material does not become a non-metal simply because it is not metallic.

What do shine and hardness tell us?

Lustre means shine; metallic lustre is the shine shown by metals. Copper, aluminium and iron appear lustrous and are hard. Coal, sulfur and wood are non-lustrous and not as hard as these metals.

Hardness does not describe every metal in the same way. Sodium and potassium are so soft that they can be cut with a knife. Mercury is a metal that is liquid at room temperature. These examples prevent an overgeneralisation from familiar solid metal objects.

How does hammering reveal malleability and brittleness?

Malleability is the property that allows a material to be beaten into thin sheets. Most metals possess this property. A piece of copper, an iron nail and a piece of aluminium become flatter when beaten with a hammer.

An ironsmith uses this ability to shape iron into useful objects. Iron is heated in a furnace and hammered to make tools, such as an axe. Other items made from iron include flat pans, buckets, tongs, spades, trowels and rakes.

How can different materials be compared?

The hammering activity compares copper, aluminium, an iron nail, coal, a pea-sized lump of sulfur and a block of wood. It requires supervision by a teacher or an adult. Appearance, hardness and response to hammering are separate observations.

1. Collect the pieces of copper and aluminium, the iron nail, coal, sulfur and wood.
2. Observe whether each material is shiny or dull and whether it is hard or soft.
3. Place each item on a hard surface and, under adult supervision, test its response to hammering.
4. Record whether it becomes slightly flattened, breaks into pieces, or shows neither of these responses.

Brittleness is the tendency to break into pieces when beaten. Coal and sulfur are brittle in this comparison. Wood neither becomes a sheet nor breaks into pieces in the activity, so it is neither malleable nor brittle in this comparison.

Where are thin metal sheets useful?

Thin silver foil placed on some sweets and aluminium foil used to wrap food illustrate malleability. Gold and silver are the most malleable metals. The ability to form a thin sheet connects a material property directly with a familiar use.

Keep the observations distinct: shine is evidence of lustre, while flattening under a hammer demonstrates malleability. A shiny appearance alone does not demonstrate that a material can form a sheet. The hammering test supplies that different piece of information.

Note: Failure to form a sheet does not automatically mean a material is brittle. Coal and sulfur break into pieces, whereas wood shows neither response in this comparison.

How do ductility and sonority explain wires and ringing sounds?

What does ductility mean?

Ductility is the property by which a material can be drawn into wires. This property is mainly possessed by metals. Copper and aluminium wires occur in electrical fittings. Metal wires also form parts of bangles, necklaces and earrings.

Wires have uses beyond electrical fittings and ornaments. They are used in stringed musical instruments such as the veena, sitar, violin and guitar. A tea strainer can also be made using metal wire. Coal and sulfur are not ductile.

Steel is a mixture of the metal iron and the non-metal carbon. Ropes made from steel wires can support heavy loads. They are therefore used in suspension bridges and in cranes that lift heavy objects.

Malleability and ductility describe different ways of shaping a material. Beating a metal into a sheet demonstrates malleability; drawing it into wire demonstrates ductility. Aluminium foil and copper wire are useful examples for keeping the two terms separate.

What does sonority mean?

Sonority is the property that enables metals to produce a ringing sound. Metals are described as sonorous. A metal spoon or coin gives a ringing sound when dropped, whereas coal and wood give dull sounds.

To compare these sounds, use a metal spoon, a coin, a piece of coal and a block of wood. Drop the objects individually from a chosen height, taking care while doing so. Listen to the character of the sound rather than confusing it with appearance.

The ringing of a school bell and of ghungroos, the small bells worn by dancers, illustrates sonority. The same broad idea links a material property with its use: the metal produces the ringing sound that the object is intended to make.

Why do metal spoons and cooking vessels transfer heat well?

Conduction of heat is the transfer of heat from one point to another within a material. Materials that transfer heat are called conductors. Metals are good conductors of heat, while wood is a poor conductor of heat.

How does the spoon comparison work?

A metal spoon and a wooden spoon can be compared using hot water. The activity must be supervised by a teacher or an adult, with care taken when handling the hot water. The spoons should be almost the same size and thickness.

1. Place a glass tumbler on a table and fill it with hot water.
2. Select a metal spoon and a wooden spoon of almost the same size and thickness.
3. Immerse both spoons in the hot water at the same time and leave them undisturbed for a few minutes.
4. Under adult supervision, carefully compare the warmth at the upper ends of the spoons.

The metal spoon becomes hotter to touch than the wooden spoon. Both have been placed in water at the same temperature for the same time. Heat has travelled along the metal spoon more effectively; the wooden spoon transfers heat poorly.

The drawing shows a metal spoon and a wooden spoon standing in a glass tumbler containing hot water. Their lower ends are immersed and their handles project above the water. Both spoons are labelled.

See Fig. 4.3 in your NCERT textbook

How does this explain the choice of cooking materials?

Mostly metal vessels are used for cooking because metals transfer heat well. Handles can be made of wood or other materials that do not conduct heat. The vessel and handle serve different purposes, so the useful property differs between them.

A copper vessel used for boiling water illustrates heat conduction. Copper also conducts electricity, but that is not the property that explains this use. Match an explanation to the process involved: heating water requires heat transfer through the cooking vessel.

How can a tester distinguish good and poor electrical conductors?

A good conductor of electricity allows electricity to pass through it easily. A poor conductor does not allow it to pass easily. A bulb tester is an electric circuit, a closed path through which electricity can flow, used to compare materials.

What does the bulb show?

In the tester activity, the bulb glows with aluminium foil, an iron nail and copper wire. Sulfur, coal, wood, stone, a rubber eraser and nylon rope do not make it glow. The materials making the bulb glow in this activity are metals.

The observation and conclusion should be kept together. A glowing bulb indicates that the tested material allows electricity through the circuit. Failure to make the bulb glow identifies a poor conductor in this comparison, provided the test circuit itself is working.

Why do tools have plastic coverings?

The plastic covering on an electrician's screwdriver and rubber gloves protect against electric shock because these materials are poor electrical conductors. Electrical conductivity describes a material's ability to carry electricity. This differs from its ability to carry heat, although metals do both well.

These tests compare properties, not just names. Wood can be compared with metals in a heat or electricity activity, but it remains outside the classification of elements as metals or non-metals. A material's behaviour in a test does not change whether it is an element.

Which conditions are necessary for iron to rust?

Rust is the brown deposit that develops on iron exposed to moist air, meaning air containing moisture. Rusting is the process of forming this deposit. An experiment with iron nails separates the effects of air and water.

What is placed in the three bottles?

Use three clean, dry glass bottles or test tubes and shining iron nails. If old nails have brown deposits, remove them with sandpaper before starting. Handle the nails carefully. The letters A, B and C are simply labels identifying the three bottles.

1. In bottle A, suspend an iron nail by a thread and add silica gel, a substance that keeps the air dry. Close the bottle tightly.
2. In bottle B, immerse a nail completely in freshly boiled and cooled water. Boiling removes dissolved gases. Add an oil layer to stop air dissolving in the water, then close the bottle tightly.
3. In bottle C, place a nail partly in water and leave the bottle open. The nail is exposed to both water and air.
4. Leave all three bottles undisturbed at room temperature and observe the changes for 8 to 10 days.

Three labelled bottle drawings show nails suspended by threads. Bottle A is capped and contains silica gel. Bottle B is capped and contains water below an oil layer. Bottle C is open, with its nail partly immersed in water.

See Fig. 4.4 in your NCERT textbook

What do the results establish?

The nails in bottles A and B show no brown deposits. The nail in bottle C develops a brown deposit. Dry air alone and water alone do not produce the deposit in these conditions. Both water and air are essential for rusting.

The special preparation of bottle B matters. It is not simply a nail placed in ordinary water: the water has been boiled and cooled, and an oil layer prevents air from dissolving back into it. Removing these details would change the intended comparison.

The three bottles provide evidence for a combined requirement. Bottle A tests dry air, bottle B tests water without access to air, and bottle C brings both together. The appearance of rust in C connects the result with moist air.

How are corrosion and rusting prevented?

Corrosion is the gradual deterioration of a metal surface caused by air, water or other substances. Rusting is the particular process involving the brown deposit on iron. Other metals can show different surface changes when exposed to the atmosphere.

Copper objects can develop a green coating, while silver objects can develop a black coating. These changes should not all be named rusting. The broader term corrosion covers deterioration of metal surfaces, whereas rusting refers specifically to iron.

What methods protect iron?

Painting, oiling and greasing can prevent iron from rusting. Another method is galvanisation, the application of a protective layer of zinc metal over iron. These methods matter because rusting damages iron structures and leads to repair or replacement.

The bottle experiment helps explain protection: preventing the necessary exposure to air and water prevents the conditions needed for rusting. Recognising those conditions connects the practical methods with the experimental evidence instead of treating them as an unrelated list.

What is remarkable about the Iron Pillar of Delhi?

The Iron Pillar of Delhi was made in the time of Chandragupta II more than 1600 years ago. It is about 8 metres high and weighs more than 6000 kilograms. Metres measure length; kilograms measure mass.

Despite exposure to wind, rainfall and intense weather over these years, the pillar has barely any rust. It was made in a way that resists rusting and demonstrates skills developed in metal technology in India. “Barely any rust” does not mean “no rust”.

What happens when magnesium and sodium meet air or water?

What does burning magnesium produce?

Magnesium is a metal that burns with a dazzling white flame. Its reaction with oxygen in air produces magnesium oxide, a white powder. An oxide is a substance formed when an element combines with oxygen.

This is a teacher demonstration. Students should wear protective eyeglasses and remain at a safe distance. The magnesium ribbon used is about 3 to 4 centimetres long; a centimetre is a unit used to measure length.

An acid-base indicator is a substance used to distinguish acidic and basic materials by a colour change. Litmus is one such indicator. A basic solution turns red litmus blue; an acidic solution turns blue litmus red.

1. Clean the magnesium ribbon by rubbing it with sandpaper.
2. Hold it with tongs, then ignite its other end using a spirit lamp or candle.
3. Allow it to burn and collect the resulting white powder on a watch glass, a shallow glass dish.
4. Add a few drops of warm water, stir, and test the mixture using an acid-base indicator.

The magnesium oxide mixture turns red litmus paper blue, so it is basic. Generally, metal oxides are basic in nature. The observed colour change supplies evidence for the nature of the product after water has been added.

A photograph shows tongs holding brightly burning magnesium above a watch glass, beside a lamp. A separate drawing shows blue and red litmus papers in a watch glass; the dipped portion of the red paper is blue.

See Figs. 4.5 and 4.6 in your NCERT textbook

Why is sodium stored in kerosene?

Sodium reacts vigorously with oxygen and water, generating a lot of heat. It is stored in kerosene to prevent exposure to moisture and air. Its behaviour shows why the conditions used to store a metal must take account of its reactions with air and water.

Keep the two examples distinct. Burning magnesium demonstrates formation of an oxide and testing its basic nature. Sodium illustrates a vigorous reaction and the need for a suitable storage liquid. Its storage is not interchangeable with the storage of phosphorus in water.

How do sulfur and phosphorus behave differently from metals?

What happens when sulfur burns?

Burning sulfur in oxygen produces sulfur dioxide gas. Dissolving this gas in water forms sulfurous acid. The resulting solution is acidic. The sequence is burning sulfur, collecting its gas, dissolving that gas in water, then testing the solution.

This activity is a teacher demonstration carried out in a fume hood or well-ventilated area. A fume hood is equipment that removes fumes from the working area. The gases from burning sulfur can be harmful if inhaled.

A deflagrating spoon is a long-handled metal spoon used to heat and burn substances in experiments. Powdered sulfur is heated in this spoon and, once burning, introduced into a gas jar or glass tumbler that is covered to retain the gas.

After 3 to 4 minutes, the lid is removed and the spoon taken out. A little water is added, the lid is quickly replaced, and the jar is shaken to dissolve the gas. Testing with an indicator reveals the acidic nature of the solution.

The drawing shows a watch glass with blue and red litmus papers. The dipped end of the blue paper is red, while the red paper remains red. Labels identify both papers and the watch glass.

See Fig. 4.7d in your NCERT textbook

Is placing sulfur in water the same experiment?

No reaction is observed when sulfur powder itself is placed in water. This differs from dissolving sulfur dioxide, the gas formed by burning sulfur. Confusing the starting substance with the product would lead to a wrong explanation of the acidic solution.

Phosphorus catches fire when exposed to atmospheric air, so it is stored in water. Sodium, by contrast, reacts vigorously with water and is stored in kerosene. The storage choice follows the particular substance's behaviour.

Which general properties describe non-metals?

Substances such as sulfur and phosphorus are usually soft and dull, neither malleable nor ductile, and not sonorous. Non-metals are generally poor conductors of heat and electricity. Most non-metals are non-lustrous, and generally non-metals do not react with water.

The oxides of non-metals are acidic in nature. The sulfur experiment illustrates this through a product dissolved in water. Compare it with the magnesium experiment, where the oxide mixture turns red litmus blue and shows a basic nature.

Why are both metals and non-metals important in everyday life?

How do properties guide the uses of metals?

The useful properties of metals explain many everyday choices. Malleability makes thin foil possible, ductility makes wires possible, heat conduction helps cooking vessels work, and electrical conduction makes copper and aluminium useful in electrical fittings. Sonority explains ringing metal bells.

Alloys are mixtures of two or more metals, or of a metal and a non-metal. Many metals and alloys are used in utensils, tools and modern technologies. Steel, containing iron and carbon, provides the example of strong wire ropes.

In India, many metals, especially iron and aluminium, are recycled. Recycling means processing used material for reuse; it helps minimise waste.

Which non-metals support life and other daily needs?

Oxygen is essential for survival and is the non-metal we breathe in. Carbon is a building block of life forms and a key component of proteins, fats and carbohydrates, which are substances needed for growth and energy.

Nitrogen is an essential plant nutrient, meaning a substance required for growth. It is used in manufacturing fertilisers, materials supplied to plants for nutrients, and other chemicals. Chlorine is commonly used in water purification, the treatment of water to make it cleaner.

A solution of iodine is applied to wounds as an antiseptic, a substance used to help prevent infection. These uses show why a dull appearance or poor conduction does not make non-metals unimportant.

Metals and non-metals therefore serve different needs. A material suitable for a wire, foil or bell is chosen for the relevant property. The non-metals needed in living things and for water treatment have equally important roles in everyday life.

Glossary

• Element — A substance that cannot be broken down into simpler substances and is a basic building block of matter.
• Metallic lustre — The shine shown by metals, such as copper, aluminium and iron.
• Malleability — The property that allows a material to be beaten into thin sheets.
• Brittleness — The tendency of a material to break into pieces when beaten.
• Ductility — The property by which a material can be drawn into wires.
• Sonority — The property that enables metals to produce a ringing sound.
• Conduction of heat — Transfer of heat from one point to another within a material.
• Electrical conductor — A material through which electricity can pass easily, as with copper.
• Rusting — Formation of a brown deposit on iron in the presence of both air and water.
• Corrosion — Gradual deterioration of metal surfaces caused by air, water or other substances.
• Galvanisation — Applying a protective layer of zinc metal over iron to prevent rusting.
• Oxide — A substance formed when an element combines with oxygen, as when magnesium burns.
• Deflagrating spoon — A long-handled metal spoon used to heat and burn substances in experiments.
• Alloy — A mixture of two or more metals, or of a metal and a non-metal.

Common errors and misconceptions

• Misconception: All metals are hard solids. Correct: Sodium and potassium are soft enough to cut with a knife, while mercury is liquid at room temperature.
• Misconception: Every material that is not a metal is a non-metal. Correct: Plastic, glass, wood, rubber and paper are not elements and are not classified as metals or non-metals.
• Misconception: Malleability means the ability to form wires. Correct: Malleability concerns sheets; ductility concerns wires. These are different properties.
• Misconception: Any material that does not flatten under a hammer must be brittle. Correct: Wood neither forms a sheet nor breaks into pieces in the comparison; coal and sulfur break.
• Misconception: Water alone is sufficient for the rusting demonstrated by the nail experiment. Correct: Both air and water are essential; the specially prepared water-only bottle shows no brown deposit.
• Misconception: Copper is useful for boiling water because it conducts electricity. Correct: The relevant property is its good conduction of heat.
• Misconception: Adding sulfur powder directly to water produces the acidic solution in the burning experiment. Correct: Sulfur dioxide must first be produced by burning sulfur, then dissolved in water.
• Misconception: Sodium and phosphorus can both be stored in water. Correct: Sodium reacts vigorously with water and is stored in kerosene; phosphorus is stored in water to prevent contact with air.

Exam-style questions with model answers

Q1. When hammered, copper becomes flatter while sulfur breaks into pieces. Name the property shown by each material and relate it to the observation. [2 marks]

1. Copper shows malleability: its flattening demonstrates the ability to be beaten into a sheet.
2. Sulfur shows brittleness: it breaks into pieces instead of forming a sheet.

Q2. Aluminium is made into foil, copper is drawn into wire, and a metal bell gives a ringing sound. Name and explain the property illustrated by each example. [3 marks]

1. Aluminium foil illustrates malleability, the property that allows a material to be beaten into thin sheets. Foil is the sheet example.
2. Copper wire illustrates ductility, the ability of a material to be drawn into wires. This differs from forming a sheet.
3. The metal bell illustrates sonority, the property enabling metals to produce a ringing sound. The sound, rather than the shape, supplies the evidence.

Q3. A metal spoon and a wooden spoon of almost the same size and thickness are immersed together in the same hot water for the same time. The metal spoon's upper end becomes hotter. Identify two comparable conditions, explain the observation, and connect it with the use of wooden handles on metal cooking vessels. [4 marks]

1. The spoons have almost the same size and thickness, so the comparison uses similarly sized objects made from different materials.
2. They are exposed to water at the same temperature for the same time, making the heating conditions comparable.
3. The metal spoon conducts heat well along its length, whereas the wooden spoon transfers heat poorly.
4. A metal cooking vessel transfers heat well, while a wooden handle uses wood's poor heat conduction.

Q4. Three clean iron nails are left for 8 to 10 days. Bottle A is tightly closed with dry air and silica gel. Bottle B is tightly closed with a nail fully in boiled and cooled water beneath oil. Bottle C is open with a nail partly in water. Only C develops brown deposits. Explain A, explain B, state the roles of boiling and oil, and give the conclusion. [5 marks]

1. Bottle A contains dry air because silica gel keeps it dry. The absence of water prevents brown deposits on its iron nail.
2. Bottle B provides water without access to air under the stated preparation. Its nail also remains without brown deposits during the observation period.
3. Boiling the water removes dissolved gases. This preparation matters because the bottle is intended to test the effect of water alone.
4. The oil layer prevents air from dissolving in the water again. The tightly closed bottle maintains the intended conditions around the nail.
5. Only bottle C exposes its nail to both air and water, and only C develops rust. Both are therefore essential for rusting in this experiment.

Q5. Magnesium burns in oxygen to give white magnesium oxide; after warm water is added, red litmus turns blue. Sulfur burns in oxygen to give sulfur dioxide; dissolving the gas in water forms sulfurous acid and turns blue litmus red. Identify the two burning products, interpret each litmus result, and state the general conclusion about metal oxides. [5 marks]

1. The product of burning magnesium is magnesium oxide, the white powder specified in the question. It forms when magnesium reacts with oxygen.
2. The magnesium oxide mixture is basic because it changes red litmus to blue. The colour change is evidence for its basic nature.
3. The product of burning sulfur is sulfur dioxide gas. It is this gas that is dissolved in water to form sulfurous acid.
4. The sulfur solution is acidic because it turns blue litmus red. This differs from the red-to-blue change in the magnesium oxide mixture.
5. Generally, metal oxides are basic in nature. The magnesium result supports that statement, while the sulfur example shows an acidic non-metal oxide product in water.

Q6. Sodium reacts vigorously with oxygen and water, generating much heat. Kerosene prevents its contact with air and moisture. Phosphorus catches fire in atmospheric air and is stored in water. Explain each storage choice and why exchanging the two storage liquids would be unsuitable for sodium. [3 marks]

1. Sodium is stored in kerosene because the liquid prevents exposure to air and moisture, the conditions associated with its vigorous reaction.
2. Phosphorus is stored in water to prevent contact with atmospheric air, since the given information says that it catches fire on exposure to air.
3. Putting sodium into water would expose it directly to a substance with which it reacts vigorously and generates much heat. The liquids are not interchangeable.

Q7. Oxygen is taken in during breathing and is required for survival, nitrogen is a plant nutrient used in fertilisers, chlorine is commonly used to purify water, and iodine solution is applied to wounds as an antiseptic. Give four points showing the everyday importance of these non-metals. [4 marks]

1. Oxygen supports survival. It is the non-metal taken in during breathing, so its importance is connected directly with life.
2. Nitrogen supports plant growth as an essential nutrient and is used in manufacturing fertilisers supplied to plants.
3. Chlorine has a role in water purification. Its commonly used treatment role shows an everyday application of a non-metal.
4. Iodine solution is used on wounds as an antiseptic. This gives another practical use for a non-metal outside plant growth and breathing.

Q8. Wood transfers heat poorly and is not an element. An element cannot be broken down into simpler substances; metals and non-metals are sub-categories of elements. Is wood classified as a non-metal? Explain using these facts. [2 marks]

1. Wood is not classified as a non-metal because it is not an element.
2. Poor heat conduction alone does not establish that a material belongs to the non-metal sub-category of elements.

Key takeaways

• Metals and non-metals are sub-categories of elements; wood, plastic, glass, rubber and paper are not included in these groups.
• Most metals are malleable, and ductility is mainly possessed by metals; sheets and wires illustrate these different properties.
• Sonorous metals produce ringing sounds, while the coal and wood used in the sound comparison produce dull sounds.
• Metals conduct heat and electricity well; these properties explain cooking vessels and electrical fittings respectively.
• Both air and water are essential for iron to rust; the three-bottle experiment separates their effects.
• Painting, oiling, greasing and galvanisation protect iron against rusting; galvanisation adds a protective zinc layer.
• Magnesium forms a basic oxide mixture in water; burning sulfur produces sulfur dioxide, which forms sulfurous acid in water.
• Sodium is stored in kerosene, while phosphorus is stored in water because their reactions require different protection.
• Oxygen, carbon, nitrogen, chlorine and iodine have important roles in life, plant growth, water treatment and wound care.

Test yourself

Which property allows aluminium to be made into foil?

Malleability allows aluminium to be beaten into thin sheets, such as foil.

How do malleability and ductility differ?

Malleability concerns forming thin sheets by beating; ductility concerns drawing a material into wires.

Why is a liquid metal not a contradiction?

Mercury is a metal that is liquid at room temperature; not every metal is solid.

What does silica gel do in the rusting experiment?

Silica gel keeps bottle A dry, allowing the experiment to test iron exposed to dry air.

Why is oil placed over boiled and cooled water?

The oil layer prevents air from dissolving in the water again after boiling has removed dissolved gases.

Which litmus change indicates the basic nature of the magnesium oxide mixture?

The mixture changes red litmus paper to blue after warm water is added.

Does sulfur powder placed directly in water produce the same result as burning sulfur first?

No reaction is observed with sulfur powder in water. Burning sulfur first produces sulfur dioxide, which forms sulfurous acid when dissolved.

What is galvanisation?

Galvanisation is applying a protective layer of zinc metal over iron to prevent rusting.