CBSE • Class 7 Science • NCERT Curiosity
The World of Metals and Non-metals
Detailed notes with chapter summary, sticky notes, definitions, physical and chemical properties, rusting diagrams, comparison tables, mind map, key points and NCERT-based, Exemplar-style and Olympiad questions.
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Chapter Summary and Sticky Notes
Central idea: Metals and non-metals are elements identified through a combination of physical and chemical properties. Their properties determine their uses, behaviour in air and water, and importance in everyday life.
✨ Metallic Lustre
Freshly exposed metal surfaces are generally shiny. The characteristic shine is called metallic lustre.
🔨 Malleability
Most metals can be beaten into thin sheets. Aluminium foil and silver foil use this property.
🧵 Ductility
Metals can generally be drawn into wires. Copper and aluminium are used in electrical wiring.
🔔 Sonority
Metals usually produce a ringing sound when struck. Bells and ghungroos use this property.
🔥 Conductivity
Metals generally conduct heat and electricity well; non-metals are usually poor conductors.
🟤 Rusting
Iron rusts only when both air and water are present. Moist air is therefore essential.
🧪 Oxides
Metal oxides are generally basic. Non-metal oxides are generally acidic.
⚠️ Exceptions
Mercury is liquid; sodium is soft; iodine is lustrous; graphite conducts electricity.
Safety: Burning magnesium and sulfur are teacher-demonstration activities. Burning sulfur produces an irritating gas and must be performed only in suitable laboratory conditions. Sodium and phosphorus must never be handled by students.
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Important Definitions
ElementA pure substance that cannot be broken down into simpler substances by ordinary chemical means.
MetalAn element that generally shows metallic lustre, malleability, ductility, sonority and good conductivity.
Non-metalAn element that generally lacks metallic properties and is usually dull, brittle and a poor conductor.
Metallic lustreThe characteristic shine seen on the surface of a metal, especially when freshly cut or polished.
MalleabilityThe property by which a material can be beaten or rolled into thin sheets.
DuctilityThe property by which a material can be drawn into thin wires.
SonorityThe property of producing a ringing sound when struck.
BrittlenessThe tendency of a material to break into pieces when hammered instead of flattening.
ConductionThe transfer of heat or electricity through a material.
ConductorA material that allows heat or electric current to pass through it easily.
Poor conductorA material that does not allow heat or electricity to pass through it easily.
Metal oxideA compound formed when a metal reacts with oxygen; metal oxides are generally basic.
Non-metal oxideA compound formed when a non-metal reacts with oxygen; non-metal oxides are generally acidic.
RustThe reddish-brown deposit formed on iron when it is exposed to both air and water.
RustingThe process of formation of rust on iron in the presence of air and water.
CorrosionThe gradual deterioration of a metal surface due to air, water or other substances.
GalvanisationProtecting iron by coating it with a thin layer of zinc.
AlloyA mixture of two or more metals, or of a metal with a non-metal, made to obtain useful properties.
Important classification: Metals and non-metals are types of elements. Plastic, glass, wood, rubber and paper are materials but are not themselves classified as metal or non-metal elements.
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Physical Properties
Lustre
Metals such as copper, aluminium and iron show metallic shine. Most non-metals are dull.
Malleability
Metals flatten into sheets when hammered; coal and sulfur are brittle and break.
Ductility
Metals can be drawn into wires. Copper wire, metal jewellery and steel cables use this property.
Sonority
Metal objects produce a ringing sound; most non-metals produce a dull sound.
Heat Conduction
Metals transfer heat well, so cooking vessels use metal bodies and poor-conducting handles.
Electrical Conduction
Copper, aluminium and iron conduct electricity; sulfur, rubber, nylon and dry wood conduct poorly.
| Property | Metals — general behaviour | Non-metals — general behaviour | Application |
|---|---|---|---|
| Lustre | Usually lustrous | Usually dull | Gold and silver jewellery |
| Hardness | Generally hard | Usually soft or brittle | Iron tools and structures |
| Malleability | Can form sheets | Not malleable; solids often break | Aluminium packaging foil |
| Ductility | Can form wires | Generally non-ductile | Copper electrical wires |
| Sonority | Usually sonorous | Usually non-sonorous | Bells and musical instruments |
| Heat conduction | Generally good | Generally poor | Metal cooking vessels |
| Electrical conduction | Generally good | Generally poor | Metal core and plastic covering in wires |
Important exceptions to remember
Mercury
A metal that is liquid at room temperature.
Sodium & potassium
Metals soft enough to be cut with a knife; they are highly reactive.
Iodine
A non-metal that has a lustrous appearance.
Graphite
A non-metallic form of carbon that conducts electricity.
Exam rule: Use words such as “generally”, “usually” and “most” while describing properties because exceptions exist.
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Rusting and Corrosion
Iron does not rust in completely dry air or in water from which air is excluded. It rusts when both oxygen from air and water are available.
Iron+Oxygen+Water→Rust
Three-bottle investigation: conditions necessary for rusting
Only Bottle C provides both air and water.
Rusting compared with corrosion
| Basis | Rusting | Corrosion |
|---|---|---|
| Meaning | Formation of reddish-brown rust on iron | Gradual deterioration of any metal surface |
| Metal involved | Specifically iron and iron-containing objects | Iron, copper, silver and other metals |
| Examples | Brown coating on an iron nail | Rust on iron, green coating on copper, black coating on silver |
| Relationship | A specific type of corrosion | The broader process |
Methods of preventing rust
🎨 Painting
Forms a barrier between iron, air and moisture.
🛢️ Oiling
Useful for moving iron parts and tools.
⚙️ Greasing
Produces a protective water-resistant layer.
🛡️ Galvanising
Coats iron with a protective layer of zinc.
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Behaviour in Air and Water
Metal + Oxygen
Magnesium burns in oxygen with a dazzling white flame and forms white magnesium oxide.
Magnesium + Oxygen → Magnesium oxideThe oxide gives a basic solution and turns red litmus blue.
Non-metal + Oxygen
Sulfur burns in oxygen and produces sulfur dioxide. The gas dissolves in water to form an acidic solution.
Sulfur + Oxygen → Sulfur dioxideWith water it forms sulfurous acid, which turns blue litmus red.
| Observation | Magnesium — metal | Sulfur — non-metal |
|---|---|---|
| On burning | Dazzling white flame | Burns and forms sulfur dioxide gas |
| Product | White magnesium oxide powder | Sulfur dioxide; dissolves in water |
| Nature of resulting solution | Basic | Acidic |
| Litmus test | Red litmus turns blue | Blue litmus turns red |
| Generalisation | Metal oxides are generally basic | Non-metal oxides are generally acidic |
Special storage cases
Sodium is stored in kerosene
Sodium reacts vigorously with air and water and releases much heat. Kerosene keeps it away from oxygen and moisture.
Phosphorus is stored in water
Phosphorus can catch fire on exposure to air. Water prevents its contact with atmospheric oxygen.
Demonstration only: Do not burn magnesium or sulfur at home. Do not smell the gas produced by burning sulfur. Sodium and phosphorus require specialised laboratory handling.
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Uses Based on Properties
| Object or use | Material chosen | Property responsible |
|---|---|---|
| Cooking vessel | Copper, aluminium, iron or steel | Good conduction of heat and ability to withstand heating |
| Cooking-vessel handle | Wood or heat-resistant plastic | Poor conduction of heat |
| Electrical wire | Copper or aluminium core | Ductility and electrical conductivity |
| Wire covering | Plastic or rubber | Poor electrical conductivity |
| Food packaging | Aluminium foil | Malleability, low cost and lightness |
| Jewellery | Gold and silver | Lustre, malleability, ductility and relatively low reactivity |
| Bells and ghungroos | Suitable metals or alloys | Sonority |
| Tools and bridges | Iron and steel | Strength, hardness and toughness |
Why non-metals are essential
Oxygen
Essential for respiration and supports many useful combustion processes.
Carbon
A basic building block of living organisms and food molecules.
Nitrogen
Used to manufacture fertilisers and is essential for plant growth.
Chlorine & iodine
Chlorine is used in water purification; iodine solution is used as an antiseptic.
Sustainability: Recycling iron, aluminium and other metals conserves resources, reduces mining, lowers waste and saves energy. Material choice should balance function, safety, cost and environmental impact.
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Important Differences
Metals and non-metals
| Basis | Metals | Non-metals |
|---|---|---|
| Appearance | Generally lustrous | Generally dull |
| State and hardness | Usually solid and hard | May be solid or gas; solids often soft or brittle |
| Malleability | Generally malleable | Not malleable |
| Ductility | Generally ductile | Not ductile |
| Sound | Usually sonorous | Usually non-sonorous |
| Heat and electricity | Generally good conductors | Generally poor conductors |
| Oxides | Generally basic | Generally acidic |
| Examples | Iron, copper, aluminium, gold | Oxygen, sulfur, nitrogen, carbon |
Malleability and ductility
| Basis | Malleability | Ductility |
|---|---|---|
| Meaning | Ability to form thin sheets | Ability to form thin wires |
| Action | Hammering or rolling | Drawing or stretching |
| Product | Metal sheet or foil | Metal wire |
| Example | Aluminium foil | Copper wire |
Conductors and poor conductors
| Basis | Good conductors | Poor conductors |
|---|---|---|
| Transfer | Allow heat or electricity to pass easily | Do not allow easy transfer |
| Examples | Copper, aluminium, iron | Rubber, plastic, sulfur, dry wood |
| Typical use | Vessel bodies and wire cores | Handles, gloves and wire coverings |
Metal oxides and non-metal oxides
| Basis | Metal oxides | Non-metal oxides |
|---|---|---|
| Formed by | Reaction of a metal with oxygen | Reaction of a non-metal with oxygen |
| General nature | Basic | Acidic |
| Litmus effect of solution | Red litmus → blue | Blue litmus → red |
| Chapter example | Magnesium oxide | Sulfur dioxide in water |
Metal, non-metal and ordinary material
| Category | Meaning | Examples |
|---|---|---|
| Metal | An element showing typical metallic properties | Iron, aluminium, copper |
| Non-metal | An element generally lacking metallic properties | Oxygen, sulfur, carbon |
| Material not itself an element | A substance or mixture used to make objects | Wood, glass, plastic, rubber, paper |
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Activities and Experimental Reasoning
Hammer Test
Observe copper, aluminium, iron, coal, sulfur and wood.
Under supervision, compare their response to gentle hammering.
Metals flatten; coal and sulfur break; wood may do neither.
Conclude malleability or brittleness from the evidence.
Sonority Test
Use objects of comparable size when possible.
Drop a metal spoon, coin, coal and wood carefully from the same height.
Compare ringing and dull sounds.
Do not identify a material from sound alone; combine properties.
Heat Conduction Test
Place similar metal and wooden spoons in hot water.
Keep immersion depth and time the same.
The upper end of the metal spoon becomes hot sooner.
Conclude that metal conducts heat better than wood.
Electrical Conduction Test
Prepare a working cell–lamp tester with free wire ends.
Insert one test material at a time.
A glowing lamp indicates electrical conduction.
Keep all other components unchanged for a fair test.
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Complete Chapter Mind Map
Metals and Non-metalsProperties → reactions → corrosion → uses → exceptions
🔩 Metals
- Usually lustrous and hard
- Malleable and ductile
- Sonorous
- Good conductors
🌿 Non-metals
- Usually dull
- Brittle if solid
- Non-sonorous
- Poor conductors
🧪 Oxides
- Metal oxide: basic
- Red litmus → blue
- Non-metal oxide: acidic
- Blue litmus → red
🟤 Corrosion
- Metal surface deteriorates
- Iron rusts in air + water
- Paint, oil, grease
- Galvanisation with zinc
🏠 Uses
- Vessels and tools
- Wires and foils
- Bells and jewellery
- Life and agriculture
⚠️ Exceptions
- Mercury: liquid metal
- Sodium: soft metal
- Iodine: lustrous non-metal
- Graphite: conductor
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Key Points for Examination
Metals and non-metals are categories of elements.
Malleability means sheets; ductility means wires.
Metals are generally lustrous, sonorous and hard.
Metals generally conduct heat and electricity well.
Most solid non-metals are brittle rather than malleable.
Metal oxides are generally basic.
Non-metal oxides are generally acidic.
Magnesium burns to form basic magnesium oxide.
Sulfur burns to form sulfur dioxide and an acidic solution.
Both air and water are necessary for rusting.
Rusting is a specific example of corrosion.
Painting, oiling, greasing and galvanising prevent rust.
Sodium is kept in kerosene; phosphorus is kept in water.
Material properties determine practical uses.
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Important Questions and Answers
These questions are independently written or adapted to cover NCERT exercise concepts, Exemplar-style reasoning and Olympiad-level application. Tap each question to reveal its answer.
NCERT-Based Questions Core Textbook
Q1.Which metal is preferred for flexible food-packaging foil because it is affordable and malleable?
Answer: Aluminium. It can be rolled into very thin sheets, is light and is less costly than metals such as gold or silver.
Q2.Which common metal may catch fire on contact with water, and how is it stored?
Answer: Sodium reacts vigorously with water and may catch fire because much heat is released. It is stored under kerosene to prevent contact with moisture and air.
Q3.Correct the statement: “Aluminium and copper are non-metals used for utensils and statues.”
Answer: Aluminium and copper are metals. They are useful because they can be shaped, are durable and conduct heat; copper is also valued for its appearance.
Q4.Correct the statement: “Solutions of metal oxides turn blue litmus red.”
Answer: Metal oxides are generally basic, so their solutions turn red litmus blue. Turning blue litmus red indicates an acidic solution.
Q5.Why are only a few metals commonly used for jewellery?
Answer: Jewellery metals such as gold and silver combine attractive lustre with malleability and ductility, so they can be shaped into detailed designs and wires. They are also comparatively resistant to rapid corrosion.
Q6.Match each use with a substance: electrical wiring, most malleable metal, respiration, fertilisers and water purification.
Answer:
- Electrical wiring — copper
- Most malleable and ductile metal — gold
- Essential for respiration — oxygen
- Used in fertilisers — nitrogen
- Used in water purification — chlorine
Q7.Compare what happens when magnesium and sulfur react with oxygen.
Answer: Magnesium burns with a dazzling white flame and produces white magnesium oxide. Its solution is basic and turns red litmus blue. Sulfur forms sulfur dioxide; when dissolved in water it gives an acidic solution that turns blue litmus red. Thus, the metal oxide is basic while the non-metal oxide is acidic.
Q8.Choose the most suitable material for a pan from iron, copper, sulfur, coal, plastic, wood and cardboard. Give reasons.
Answer: Copper is the best choice from the list because it conducts heat efficiently and can be shaped into a pan. Iron could also be used but conducts heat less efficiently. Sulfur and coal are brittle; plastic, wood and cardboard are poor heat conductors and may burn or soften.
Q9.Iron nails are separately immersed in oil, water and vinegar. Which nail is least likely to rust, and why?
Answer: The nail immersed in oil is least likely to rust because oil keeps both water and air away from its surface. Water contains dissolved air and can support rusting; vinegar may speed up corrosion.
Q10.How do properties determine the everyday uses of metals and non-metals?
Answer: Conductive metals are used for wires and cookware; malleable metals form sheets and containers; ductile metals form wires; sonorous metals make bells; strong metals make tools. Oxygen supports respiration, nitrogen supports plant growth and fertiliser production, chlorine purifies water, and iodine solution acts as an antiseptic.
Q11.Why cannot sulfur replace zinc as a protective coating on iron merely because sulfur does not react with water?
Answer: A protective coating must form a tough, continuous and strongly attached layer. Zinc is a malleable metal that can coat iron effectively. Sulfur is brittle and non-malleable, so it cannot form a durable protective sheet over iron. Non-reaction with water alone is not sufficient.
Q12.Why does an ironsmith heat iron before shaping it into tools?
Answer: Heating makes iron softer and easier to deform. Its malleability increases, so the ironsmith can hammer it into the required shape with less effort. After cooling, the tool becomes hard again.
Exemplar-Style Questions Reasoning & Application
Q13.A shiny solid breaks into pieces when hammered and does not conduct electricity. Can it be classified as a metal from shine alone?
Answer: No. One property is insufficient. Although it is shiny, its brittleness and poor conductivity are typical of a non-metal. Some non-metals, such as iodine, are lustrous. Classification should use several properties.
Q14.Why are metal cooking vessels provided with wooden or heat-resistant plastic handles?
Answer: The metal body conducts heat efficiently to the food. Wood or suitable plastic conducts heat poorly, so the handle remains cooler and safer to hold.
Q15.Why is magnesium ribbon cleaned with sandpaper before burning?
Answer: Magnesium develops a thin oxide coating in air. Rubbing removes this coating and exposes fresh metal, allowing the ribbon to ignite and burn more readily.
Q16.In the rusting experiment, why is water boiled and then covered with oil in Bottle B?
Answer: Boiling removes much of the dissolved air from water. The oil layer prevents atmospheric air from dissolving again. Thus, the nail has water but little or no oxygen, testing whether water alone causes rusting.
Q17.Why is silica gel placed in Bottle A?
Answer: Silica gel absorbs moisture and keeps the air dry. This creates a condition with air but without water, allowing a fair test of whether dry air alone causes rust.
Q18.Distinguish rusting and corrosion using one example of each.
Answer: Rusting is the formation of reddish-brown rust specifically on iron in air and water. Corrosion is the wider deterioration of metals, such as the green coating on copper. Rusting is therefore one type of corrosion.
Q19.A substance is ductile, sonorous and conducts electricity. What is its most likely category?
Answer: It is most likely a metal because ductility, sonority and good electrical conductivity together are characteristic metallic properties. Multiple observations make the conclusion stronger.
Q20.Why is “all non-metals are poor conductors” an unsafe absolute statement?
Answer: It ignores exceptions. Graphite, a form of the non-metal carbon, conducts electricity. Therefore, the scientifically accurate statement is that non-metals are generally poor conductors.
Q21.A white oxide solution turns red litmus blue. Was the original element more likely magnesium or sulfur?
Answer: Magnesium. Magnesium is a metal and forms magnesium oxide, which produces a basic solution. A basic solution turns red litmus blue. Sulfur forms an acidic oxide.
Q22.Why should the size, immersion depth and time be kept similar in the metal-spoon and wooden-spoon heat experiment?
Answer: These are control variables. Keeping them similar ensures that the observed difference is mainly due to the spoon material rather than size, exposed length or heating time.
Olympiad Challenge Higher-Order Thinking
Q23.A material is liquid at room temperature, shiny and conducts electricity. Identify a likely element.
Answer: Mercury. It is an important exception because it is a metal but remains liquid at room temperature.
Q24.Four nails are kept in dry air, boiled water with oil, ordinary tap water open to air, and salty water open to air. Arrange the expected rusting from least to greatest.
Answer: Dry air ≈ boiled water protected by oil < ordinary tap water open to air < salty water open to air. The first two lack one essential condition. Tap water has air and water. Dissolved salt generally speeds the corrosion process.
Q25.Design the safest pan using copper, wood and plastic. Which material goes where?
Answer: Use copper for the pan body because it conducts heat well and can be shaped. Use a suitable heat-resistant poor conductor for the handle—wood is appropriate when properly designed. Ordinary plastic should be used only if it is heat-resistant and kept away from direct flame.
Q26.Why can steel wire ropes support suspension bridges even though carbon is a non-metal?
Answer: Steel is an alloy in which iron is combined with carbon and sometimes other elements. The combination gives high strength and toughness, while the metal-rich alloy can be formed into strong wires. An alloy’s properties differ from those of its individual components.
Q27.A student concludes that wood is a brittle non-metal because it does not flatten under a hammer. Find two errors.
Answer: First, failure to flatten does not automatically mean brittleness; brittle materials break into pieces, while wood may do neither. Second, wood is a complex material and not an element, so it is not classified as a non-metal element.
Q28.Which is the better evidence that an unknown sample is a metal: shine alone or malleability plus electrical conductivity? Explain.
Answer: Malleability plus electrical conductivity is stronger evidence because it combines two independent characteristic properties. Shine alone is unreliable since lustrous non-metals such as iodine exist and surfaces can be coated or polished.
Q29.Magnesium oxide solution and sulfur dioxide solution are unlabeled. How can litmus identify them?
Answer: Test separate samples with both red and blue litmus. Magnesium oxide solution is basic and turns red litmus blue. Sulfur dioxide solution is acidic and turns blue litmus red. Use fresh strips and separate droppers.
Q30.Why do painting, oiling and galvanising all prevent rust despite using different materials?
Answer: Each method creates a barrier that prevents or reduces contact between iron and the two substances needed for rusting—oxygen and water. Galvanising additionally provides a firmly attached zinc layer.
Q31.Assertion: An iron nail fully covered with grease does not rust easily. Reason: Grease separates iron from air and moisture.
Answer: Both the Assertion and Reason are true, and the Reason correctly explains the Assertion. Grease forms a protective barrier, so the conditions required for rusting are not available at the iron surface.
Q32.A smartphone contains conducting metals, insulating materials and several non-metals. Why is no single category sufficient?
Answer: Different functions require different properties. Metals carry current, form contacts, dissipate heat and provide strength. Insulators separate conducting paths. Non-metals occur in display materials, battery compounds and electronic components. A working phone therefore depends on carefully selected combinations.
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One-Minute Revision Capsule
IDENTIFY
Observe lustre, hardness, malleability, ductility, sound and conductivity.
Observe lustre, hardness, malleability, ductility, sound and conductivity.
→
TEST
Study behaviour with oxygen, water and indicators; use several properties.
Study behaviour with oxygen, water and indicators; use several properties.
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APPLY
Select materials for tools, wires, vessels, protection, health and agriculture.
Select materials for tools, wires, vessels, protection, health and agriculture.
Final recall: Metals—shine, sheets, wires, ringing, conduction and basic oxides. Non-metals—generally dull, brittle, poor-conducting and acidic oxides. Air + water causes rust.
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