Metals and Non-Metals | ICSE Class 7 Chemistry Notes

This note covers the classification of elements, physical properties of metals and non-metals, common uses, corrosion, the conditions needed for rusting, methods of protecting iron, and the properties and uses of metalloids.

What are metals and non-metals?

An element is a substance that cannot be broken down into simpler substances by chemical methods. Iron, copper, aluminium, oxygen, carbon and sulphur are elements. Metals and non-metals are groups of elements distinguished by their properties.

A physical property is a characteristic, such as appearance or the ability to conduct heat, that can be examined without changing a substance into another substance. Comparing several physical properties helps us recognise the general behaviour of metals and non-metals.

Which elements belong to each group?

Lustre means the shine of a surface. Malleability means the ability to be beaten into thin sheets, while ductility means the ability to be drawn into wires. A conductor allows heat or electricity to pass through it readily.

Generally, metals are lustrous, whereas most non-metals are non-lustrous. Rubbing a metal surface with sandpaper can reveal its shine. A dull surface on an old metal object does not by itself show that the material is a non-metal.

Does every material fit into these groups?

Wood, plastic, glass, rubber and paper are not classified as metallic or non-metallic elements because they are not elements. They can still be compared with metals when investigating properties such as heat conduction.

Note: General properties have exceptions. Iodine is a lustrous non-metal, and mercury is a metal that is liquid at room temperature. Do not identify an element from shine or physical state alone.

How do malleability, ductility, hardness and strength differ?

Malleability describes the ability of a material to be beaten into thin sheets. Most metals possess this property. Copper, aluminium and iron can become flattened when struck with a hammer. Gold and silver are the most malleable metals.

Aluminium foil used for wrapping food and thin silver foil used on some sweets illustrate malleability. The important change is from a thicker piece to a thin sheet. A sheet is different from a wire.

What happens to brittle materials?

A brittle material breaks into pieces rather than flattening under a blow. Coal and sulphur are brittle. In a comparison with metal samples, their breaking into pieces is the observation that distinguishes them from materials that form sheets.

For a supervised comparison, place copper, aluminium, an iron nail, coal and sulphur on a hard surface and test them separately. Record whether each sample flattens or breaks. The activity involves hammering and requires adult supervision.

Ductility describes the ability to be drawn into wires. Copper and aluminium wires occur in electrical fittings. Metal wires also have uses in ornaments and stringed musical instruments. Coal and sulphur are not ductile.

Are hardness and strength the same property?

Hardness is resistance to scratching or compression, meaning being pressed into a smaller space. Metals are generally hard, but their hardness varies. Sodium and potassium are so soft that they can be cut with a knife. They are exceptions, not suitable materials for an ordinary classroom hammering activity.

Strength is the ability to withstand a force, a push or pull, without breaking. Steel wire ropes can support heavy loads and are used in suspension bridges and cranes. Steel is a mixture containing iron and carbon. Hardness, strength, malleability and ductility describe different aspects of a material's behaviour.

What is sonority, and how can it be observed?

Sonority is the property of producing a ringing sound when struck. A material showing this property is called sonorous. Metals are sonorous in nature, which helps explain their use in bells.

A metal spoon and a metal coin produce ringing sounds when dropped onto a hard surface. Coal and wood produce dull sounds in the same comparison. Non-sonorous does not mean completely silent: the distinction is the absence of the characteristic ringing sound.

How should the sounds be compared?

1. Select a metal spoon, a metal coin, a piece of coal and a block of wood.
2. Drop the objects carefully, one at a time, onto a hard surface.
3. Listen to each sound and record whether it is ringing or dull.
4. Compare the metallic objects with coal and wood before drawing a conclusion.

The ringing of a school bell and the sound of ghungroos, small bells worn by dancers, illustrate this property. Sonority concerns sound; lustre concerns appearance. Naming the correct property is essential when explaining why a material suits a particular use.

This comparison provides another observation to combine with malleability and conduction. Wood is included as a familiar comparison material, but it is not a non-metallic element. A material's behaviour in one test does not make it an element.

How do metals conduct heat?

Conduction of heat is the transfer of heat from one point to another through a material. Metals are good conductors of heat. Wood is a poor conductor, meaning that heat passes through it much less readily in the comparison.

This property helps explain why cooking vessels are mostly made from metals. Their handles can be made from wood or other materials that do not conduct heat readily. The vessel and its handle perform different functions and therefore need different properties.

What does the spoon comparison show?

1. Under adult supervision, place hot water in a glass tumbler.
2. Select a metal spoon and a wooden spoon of almost the same size and thickness.
3. Immerse both spoons in the same hot water simultaneously and leave them for a few minutes.
4. Compare how warm their upper ends become, taking care with hot water and hot objects.

The upper end of the metal spoon becomes hotter than that of the wooden spoon. Both spoons have been in water at the same temperature for the same time. This comparison shows that heat travels through the metal spoon more readily.

A glass tumbler contains water and two spoons. The spoons are labelled “Metal spoon” and “Wooden spoon”, with their upper ends projecting above the water.

See Fig. 4.3 in your NCERT textbook

Metals do not all conduct heat equally well. Silver and copper are the best conductors of heat, while lead and mercury are comparatively poor conductors of heat. The word “comparatively” matters: it compares these metals with other metals.

How can electrical conduction distinguish materials?

Electrical conduction is the passage of electricity through a material. Good conductors allow electricity to pass easily. Poor conductors do not allow it to pass readily. Metals are good conductors of electricity.

An electric circuit is a connected path through which electric current can flow. Electric current means the flow of electric charge. A battery supplies electrical energy, and a bulb can show whether current is flowing through a simple tester circuit.

How does a tester work?

Connect a battery, bulb, switch and connecting wires, leaving a gap for the sample. A switch opens or closes the path. Place the sample between the two clips at the gap, then close the switch to test it.

The drawing shows a battery connected by wires to a bulb, a switch and two clips. The clips are labelled A and B, which identify the two ends of the gap where the test sample is inserted.

See Fig. 3.2 in your NCERT textbook

Aluminium, iron and copper make the bulb glow in a working tester circuit. Sulphur, coal, dry wood, rubber and nylon do not make it glow in this comparison. A glowing bulb provides evidence that the sample allows current to pass.

Insulators are materials that conduct electricity poorly. Rubber or plastic coverings around conducting parts help protect people from electric shock. The metal inside a wire and its outer covering have different jobs.

Which non-metal is an exception?

Graphite, a form of carbon, conducts electricity. Therefore, the statement that non-metals are generally poor electrical conductors must not be changed to “no non-metal conducts electricity”. Conducting electricity does not turn graphite into a metal.

How do melting point, boiling point and density compare?

The melting point is the temperature at which a solid changes into a liquid at a given pressure. Pressure means force acting per unit area. The boiling point is the temperature at which a liquid boils and changes into a gas at a given pressure.

Metals usually have high melting and boiling points. Non-metals usually have low melting and boiling points, with exceptions such as carbon. These are general comparisons, not statements that every metal melts above every non-metal.

Why must exceptions be remembered?

Mercury is liquid at room temperature. Gallium and caesium have very low melting points. Sodium and potassium are soft metals with low melting points and low densities. Such exceptions show why a single property cannot provide a complete classification.

Carbon occurs in different forms called allotropes. Diamond and graphite are allotropes of carbon. Diamond is the hardest natural substance known and has a very high melting and boiling point. Graphite conducts electricity, although carbon is a non-metal.

What does density mean?

Density means mass per unit volume. Mass is the amount of matter in an object; volume is the space it occupies. Comparing equal volumes makes density meaningful: the sample with the greater mass has the greater density.

Metals generally have high densities, while non-metals generally have low densities. This comparison has exceptions. It is misleading to compare the heaviness of two objects without considering their volumes, or to assume that all metals have the same density.

What are corrosion and rusting?

Definition: Corrosion is the gradual deterioration of a metal's surface through the action of air, water or other substances in its surroundings.

Rusting is the formation of rust on iron. Rust is the brown, flaky deposit that develops when iron is exposed to moist air. Moist air contains water vapour, the gaseous form of water.

Iron needs both oxygen and water for rusting. Oxygen is a gas present in air. Water can be supplied by moisture in the surroundings. The presence of water alone or dry air alone does not produce rust in the controlled comparison described below.

Do other metals also corrode?

Rusting can be summarised in words as iron + oxygen + water → rust. Here, + means “reacts with” and → means “forms”. A chemical reaction is a change in which new substances form.

Copper reacts with carbon dioxide, a gas in air, in moist conditions to develop its green coating. Silver reacts with sulphur in the air to form its black coating.

Rusting is one example of corrosion. The green coating on copper and black coating on silver are not iron rust. Different metals can form different substances when they react with their surroundings.

Rusting damages iron articles and structures, creating a need for repair or replacement. Understanding the conditions that cause rusting therefore helps explain how protective coatings work. The aim is to stop the metal's exposure to the substances that cause the damage.

The Iron Pillar of Delhi illustrates resistance to rusting. Despite long exposure to weather, it has barely any rust. This shows the skill involved in its manufacture; it does not mean that ordinary iron articles are unaffected by moist air.

How does the three-bottle experiment show the conditions for rusting?

Use three clean glass bottles with iron nails to compare dry air, water without dissolved air, and water together with air. Label the bottles A, B and C; these letters identify the three experimental arrangements.

How are the bottles prepared?

1. Clean the iron nails. Remove old brown deposits with sandpaper so that any new deposit can be recognised.
2. In bottle A, place a nail and silica gel, a substance that absorbs moisture and keeps the air dry. Close the bottle tightly.
3. In bottle B, immerse a nail completely in freshly boiled and cooled water. Add an oil layer and close the bottle tightly.
4. In bottle C, partly immerse a nail in water and leave the bottle open so that both water and air are available.
5. Leave the bottles undisturbed at room temperature and observe them for 8 to 10 days.

Boiling removes dissolved gases from the water used in bottle B. The oil layer prevents air from dissolving in it again. Both details are necessary: an ordinary bottle of water can contain dissolved air and is not the same experimental condition.

Three bottles contain nails suspended by threads. Capped bottle A contains silica gel. Capped bottle B contains water with an oil layer above it. Open bottle C contains a nail partly immersed in water.

See Fig. 4.4 in your NCERT textbook

What do the observations mean?

The comparison supports the conclusion that both air and water are needed for rusting under these conditions. Bottle A tests the absence of moisture; bottle B tests the absence of air. Bottle C supplies both and provides the contrasting result.

How can iron be protected from rusting?

Rusting can be prevented by protecting iron from direct contact with air and water. Painting, oiling and greasing place a protective covering on its surface. Their purpose follows directly from the conditions needed for rust formation.

Metal coatings provide other methods. The coating is a layer of another metal placed over the article. Different methods have different names because they use different coating metals.

Which protective methods should be distinguished?

Galvanisation specifically means coating iron or steel with zinc. It does not mean coating with any metal. Galvanised iron pipes used to carry water illustrate this application. Tinning and chrome plating use tin and chromium respectively.

Keeping a paint covering intact matters because exposed iron can again meet air and water. Zinc has an additional protective effect: a galvanised article is protected against rusting even if its zinc coating is broken. This special behaviour should not be assumed for every coating.

Can mixing metals change their properties?

An alloy is a uniform mixture of two or more metals, or of a metal and a non-metal. Uniform means that its composition is the same throughout. Alloying can change the properties of the original metal.

Stainless steel contains iron mixed with nickel and chromium and does not rust. It differs from an iron object with a coating: the added substances are mixed into the material. A coating covers the surface, while alloying changes the material itself.

The common idea behind choosing a protective treatment is to reduce corrosion. The precise method must still be named correctly, especially when distinguishing zinc coating, tin coating, chromium coating and the formation of an alloy.

How are the properties of metals and non-metals linked to their uses?

A useful explanation connects a material to the property required for its job. A metal used for a wire must be capable of forming a wire; a conductor in an electrical circuit must also allow current to pass. These are separate requirements.

What are common uses of metals?

Solder is an alloy used for joining metal parts. Lead and tin form a solder with a low melting point. Its use belongs to the alloy, so it should not be described as if the solder were pure lead.

Pure gold is very soft and unsuitable for making jewellery on its own. Adding silver or copper makes it harder. Thus, choosing a metal may involve changing its properties through alloying as well as using its original shine and ease of shaping.

Why are non-metals also important?

An antiseptic is a substance used on living tissue to help prevent infection. Iodine solution is an example. The use refers to a preparation containing iodine, not to placing a solid piece of iodine on a wound.

Proteins, fats and carbohydrates are groups of substances in food and living organisms that support growth and energy needs. The importance of carbon, oxygen and nitrogen shows why usefulness cannot be judged by whether an element is metallic.

What are metalloids, and why are they useful?

Metalloids, also called semi-metals, are elements with properties characteristic of both metals and non-metals. Silicon, germanium and antimony are examples. This mixed behaviour is another reason to compare several properties instead of relying on a single observation.

A metalloid is an element in its own right. It is not a mixture made by combining a metal and a non-metal. That distinction separates a metalloid such as silicon from an alloy such as steel.

What is a semiconductor?

A semiconductor is a material whose electrical conductivity is intermediate between that of metals and insulators. Electrical conductivity describes how readily a material allows current to pass. Silicon and germanium are semiconductor materials used in electronic devices.

Their usefulness is connected with controlling electrical conduction. Adding a small amount of a suitable substance can increase a semiconductor's conductivity. This deliberate addition is called doping; antimony is one substance used for doping silicon or germanium.

These examples distinguish classification from use. Silicon and germanium are metalloids by their combination of properties and are useful as semiconductors. Antimony is also a metalloid and can help modify the conducting behaviour of semiconductor materials.

Note: Tungsten is a metal. Its strength and high melting point make it useful for bulb filaments, the thin parts of filament bulbs that become hot and emit light. It should not be classified as a metalloid.

Glossary

• Element — A substance that cannot be broken down into simpler substances by chemical methods.
• Lustre — The shine of a surface, commonly seen when a metal surface is clean.
• Malleability — The property that allows a material to be beaten into thin sheets.
• Ductility — The property that allows a material to be drawn into thin wires.
• Brittleness — The tendency of a material to break into pieces rather than flatten under a blow.
• Sonority — The property of producing a ringing sound when a material is struck.
• Conduction — The passage of heat or electricity through a material from one place to another.
• Density — Mass per unit volume, used to compare how much matter occupies a given space.
• Melting point — The temperature at which a solid changes into a liquid at a given pressure.
• Boiling point — The temperature at which a liquid boils and becomes a gas at a given pressure.
• Corrosion — Gradual deterioration of a metal surface caused by air, water or other substances.
• Rusting — Formation of a brown rust deposit on iron in the presence of air and water.
• Galvanisation — Protection of iron or steel against rusting by applying a thin coating of zinc.
• Alloy — A uniform mixture of two or more metals, or of a metal and a non-metal.
• Metalloid — An element showing properties characteristic of both metals and non-metals, such as silicon.

Common errors and misconceptions

• Misconception: Every metal is hard and solid at room temperature. Correct: Sodium and potassium are soft metals, and mercury is a liquid at room temperature.
• Misconception: Malleability means drawing a material into wires. Correct: Malleability concerns sheets; ductility concerns wires. They describe different ways of shaping a material.
• Misconception: Every shiny element is a metal. Correct: Iodine is a lustrous non-metal, so appearance alone cannot establish the classification.
• Misconception: Non-metals cannot conduct electricity. Correct: Non-metals are generally poor conductors, but graphite, a form of carbon, conducts electricity.
• Misconception: A non-sonorous material produces no sound. Correct: Coal and wood produce dull sounds; they do not produce the characteristic metallic ringing sound.
• Misconception: Water alone is enough for iron to rust. Correct: Both air and water are required in the rusting experiment; boiled water protected from air does not produce rust.
• Misconception: Galvanisation uses tin, and every corroded metal is rusty. Correct: Galvanisation uses zinc. Rusting refers to iron; copper and silver develop different corrosion coatings.
• Misconception: A metalloid is an alloy containing a metal and a non-metal. Correct: A metalloid is an element. An alloy is a mixture of elements.

Exam-style questions with model answers

Q1. Aluminium can be beaten into thin foil, and copper can be drawn into wires. Name the property shown in each case. [2 marks]

1. Aluminium shows malleability, the property that allows a material to be beaten into thin sheets.
2. Copper shows ductility, the property that allows a material to be drawn into thin wires.

Q2. Iodine is lustrous but is a non-metal. Graphite conducts electricity but is also a non-metal. Use these facts to correct the claims that all shiny elements and all conducting elements are metals. [2 marks]

1. Shine alone does not establish that an element is a metal: iodine is the given lustrous non-metal exception.
2. Electrical conduction alone does not establish that an element is a metal: graphite is the given conducting non-metal exception.

Q3. A metal spoon and a wooden spoon of almost the same size and thickness are placed in the same hot water for the same time. The upper end of the metal spoon becomes hotter. Identify the process, explain the difference, and give the matching arrangement of materials in cooking vessels and handles. [3 marks]

1. The process is conduction of heat: heat passes through the material from the immersed part of each spoon towards its upper end.
2. The metal conducts heat more readily than wood. The shared water temperature and time allow the observed difference to be linked to the materials.
3. Metal is suitable for the cooking vessel because it conducts heat; wood is suitable for a handle because it is a poor conductor.

Q4. In a working battery-and-bulb tester, copper and aluminium make the bulb glow, while sulphur and dry wood do not. Copper and aluminium can be drawn into wires; wood is not an element. Explain the results, identify a suitable wire material, and state why dry wood should not be called a non-metallic element. [4 marks]

1. Copper and aluminium allow electric current to pass through the tester, so the bulb glows. Both are good electrical conductors.
2. Sulphur and dry wood do not make the bulb glow in the comparison because they do not allow electricity to pass readily.
3. Copper or aluminium is suitable for the conducting part of a wire because it conducts electricity and can be drawn into wires.
4. Dry wood is not an element. Metals and non-metals are classifications of elements, so poor conduction does not make wood a non-metallic element.

Q5. Clean iron nails are placed in three bottles. Bottle A contains dry air and moisture-absorbing silica gel. Bottle B contains freshly boiled and cooled water under oil and is tightly closed. Bottle C is open, with its nail partly immersed in water. After 8 to 10 days, only C has brown rust. Explain each bottle's result, the oil's role, and the overall conclusion. [5 marks]

1. Bottle A does not show rust because silica gel removes moisture. Air is present, but the water needed for rusting is missing.
2. Bottle B does not show rust because boiling removed dissolved gases. The nail is in water that has been protected from renewed contact with air.
3. The oil layer in bottle B prevents air from dissolving in the water again, helping maintain the intended condition throughout the comparison.
4. Bottle C develops brown rust because the partly immersed nail has access to both water and air through the open bottle.
5. The combined results show that both air and water are needed for rusting under these conditions. Removing either one prevents the observed rust deposit.

Q6. Iron rusts when exposed to air and water. Explain how painting and oiling help, and name the coating metal used in galvanisation, chrome plating and tinning. Give five separate points. [5 marks]

1. Painting covers the iron surface with a layer of paint. An intact covering separates the iron from the air and water needed for rusting.
2. Oiling forms a protective film on the iron. This reduces direct contact between its surface and the air and moisture in the surroundings.
3. Galvanisation coats iron or steel with a thin layer of zinc. It is a specific protective treatment, rather than a general name for metal coating.
4. Chrome plating places a layer of chromium on the article. The chromium forms a protective coating over the underlying metal surface.
5. Tinning places a layer of tin over the article. This protective surface covering is different from the zinc layer used in galvanisation.

Q7. Silicon and germanium are elements with properties of both metals and non-metals. Their electrical conductivity is intermediate between metals and insulators, and their conduction can be controlled for use in electronic devices. Name their class, explain the term semiconductor, and link that property to their use. [3 marks]

1. Silicon and germanium are metalloids because they show properties characteristic of both metals and non-metals. Each is an element, rather than a mixture.
2. A semiconductor has electrical conductivity intermediate between metals and insulators. Silicon and germanium are examples of this type of material.
3. Their semiconductor behaviour makes them useful in electronic devices where electrical conduction must be controlled. This connects their use with an electrical property.

Q8. Match these uses to the correct substances and explain each match: oxygen supports respiration; nitrogen is used to manufacture fertilisers; chlorine is used to purify water. Uses: supplying nutrients for plant growth, releasing energy from food in living cells, and water purification. [3 marks]

1. Nitrogen matches the plant-growth use because it is used to manufacture fertilisers. Fertilisers supply nutrients needed for plants to grow.
2. Oxygen matches the release of energy from food because it supports respiration. Respiration is the process by which living cells release energy from food.
3. Chlorine matches water purification, which is its stated use. This is an example of a useful non-metal in everyday life.

Key takeaways

• Metals and non-metals are groups of elements; wood, plastic, rubber and glass are not non-metallic elements.
• Most metals are malleable, and metals are generally ductile; sheets demonstrate malleability, while wires demonstrate ductility.
• Metals conduct heat and electricity well, but different metals do not conduct heat equally well.
• General properties have exceptions: iodine is lustrous, graphite conducts electricity, and mercury is liquid at room temperature.
• Rusting is the corrosion of iron; its brown deposit forms when both air and water are available.
• Painting, oiling, greasing and metal coatings help protect iron; galvanisation specifically uses a zinc coating.
• Uses depend on properties: copper conducts electricity, aluminium forms foil, and metals produce ringing sounds in bells.
• Metalloids are elements with mixed metallic and non-metallic properties; silicon and germanium are useful semiconductor materials.

Test yourself

Why is foil evidence of malleability rather than ductility?

Foil is a thin sheet formed from a material. Malleability concerns sheets, while ductility concerns drawing a material into wires.

What distinguishes a sonorous material from one that merely makes a sound?

A sonorous material produces a ringing sound when struck. A non-sonorous material may still make a dull sound.

Which property explains the use of copper in a cooking vessel?

Copper is a good conductor of heat, so heat can pass readily through the vessel during cooking.

Give a non-metal that conducts electricity and one that is lustrous.

Graphite, a form of carbon, conducts electricity. Iodine is a non-metal with a lustrous appearance.

Why is oil placed over boiled water in the rusting experiment?

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

How do galvanisation, tinning and chrome plating differ?

Galvanisation coats iron or steel with zinc; tinning uses tin; chrome plating uses chromium as the coating metal.

Is the green coating on copper iron rust?

No. It is a product of copper corrosion. Rusting specifically refers to the formation of rust on iron.

How does a metalloid differ from an alloy?

A metalloid is an element with properties of metals and non-metals. An alloy is a uniform mixture of elements.