Materials around us can be classified into two main groups: **Metals** and **Non-metals**. Understanding their properties helps us use them wisely in daily life.
**Exceptions:** Not all metals follow all these rules:
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**Definition:** The property by which materials can be beaten into thin sheets without breaking is called **malleability**. Materials showing this property are called **malleable**.
**Which materials are malleable?**
**Real-life examples:**
**Which materials are NOT malleable?**
**Brittleness:** Materials that break into small pieces when beaten are called **brittle**. Coal and sulfur are examples of brittle non-metals.
**Activity 4.1 Observation Table:**
When you hammer different materials:
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**Definition:** The property by which materials can be drawn into thin wires is called **ductility**. Materials showing this property are called **ductile**.
**Which materials are ductile?**
**Real-life examples from India:**
**Important fact:** Steel is a mixture of iron (metal) and carbon (non-metal). Steel wire ropes are very strong and can support heavy loads.
**Which materials are NOT ductile?**
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**Definition:** The property of metals that enables them to produce a **ringing sound** when struck is called **sonority**. Such metals are called **sonorous**.
**Real-life examples from India:**
**Sound comparison:**
**Activity 4.2:** When you drop metal objects and non-metal objects from the same height, metals produce a clear ringing sound while coal and wood produce dull sounds.
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**Definition:** The transfer of heat from one point to another within a material is called **conduction**. Materials that allow heat to pass through easily are called **conductors of heat**.
**Good conductors of heat:**
**Poor conductors of heat (insulators):**
**Activity 4.3 - Experiment with metal and wooden spoons:**
**Procedure:**
1. Take a glass tumbler and fill it with hot water
2. Place a metal spoon and wooden spoon of same size in the water simultaneously
3. Leave them undisturbed for a few minutes
4. Carefully touch the upper end of each spoon
**Observation:**
**Why?** Metals are good conductors of heat, so heat travels through them quickly. Wood is a poor conductor, so heat travels slowly.
**Real-life applications in Indian kitchens:**
**Important:** This property of metals makes them perfect for cooking because heat transfers quickly from the flame to the food.
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**Definition:** The property of materials to allow electric current to flow through them is called **electrical conductivity**. Materials that allow electricity to flow easily are **good conductors** of electricity. Those that prevent electricity flow are **poor conductors** (insulators).
**Good conductors of electricity:**
**Poor conductors of electricity (insulators):**
**Activity 4.4 - Electrical Tester Activity:**
**Materials tested:**
**Pattern:** All materials that make the bulb glow are **metals**. All materials that don't conduct electricity are **non-metals**.
**Real-life safety applications:**
**Why this matters:** Using insulating materials (poor conductors) around electrical equipment protects us from dangerous electric shocks.
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**Definition:** The brown deposit that forms on iron objects is called **rust**. The process of formation of rust on iron is called **rusting**.
**What causes rust?**
Rust forms only when iron comes into contact with **BOTH air AND water (moist air)**. Neither air alone nor water alone causes rusting.
**Activity 4.5 - Rusting Experiment:**
**Setup with three glass bottles (A, B, C):**
**Bottle A - Dry air only:**
**Bottle B - Water only (no air):**
**Bottle C - Both air and water (moist air):**
**Key finding:** **Moist air is responsible for rusting of iron**. The presence of both oxygen (from air) and water is essential.
**Chemical process:** When iron is exposed to moist air, it reacts with oxygen and water to form iron oxide (rust).
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**Definition:** **Corrosion** is the gradual deterioration of metal surfaces caused by air, water, or other substances.
**Examples of corrosion in different metals:**
**Difference between rusting and corrosion:**
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**Problem:** Rusting of iron is a serious economic problem in India. Every year, enormous amounts of money are spent to replace or repair iron structures damaged by rusting.
**Methods to prevent rusting:**
1. **Painting** - sealed coat prevents air and water contact
2. **Oiling** - oil layer prevents moisture
3. **Greasing** - grease layer prevents air and water contact
4. **Galvanisation** - coating with protective zinc metal layer
**Real-life examples:**
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**The Iron Pillar (Delhi):**
**What this tells us:**
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**Activity 4.6 - Magnesium Burning Experiment:**
**Materials:**
**Procedure:**
1. Clean magnesium ribbon by rubbing with sandpaper
2. Hold it with tongs
3. Ignite the ribbon using spirit lamp or candle
4. Let it burn completely
5. Collect the white powder in a watch glass
**Observations:**
**Chemical reaction:**
Magnesium + Oxygen (from air) → **Magnesium oxide** (white powder)
**Testing the nature of magnesium oxide:**
1. Add a few drops of warm water to the white powder
2. Stir well
3. Test with **red litmus paper** and **blue litmus paper**
**Result:** Red litmus paper turns **blue** → magnesium oxide solution is **basic in nature**
**Important fact:** **Oxides of metals are generally basic in nature**
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**Sodium characteristics:**
**Why kerosene storage?**
**Oxide nature:** Sodium oxide is also basic in nature (like other metal oxides)
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**Activity 4.7 - Burning of Sulfur:**
**Materials:**
**Procedure:**
1. Place sulfur powder in deflágrating spoon
2. Heat it on a flame
3. When sulfur starts burning, introduce the spoon into a gas jar
4. Cover the gas jar with a lid
5. After 3-4 minutes, remove the lid and take out the spoon
6. Add small quantity of water into the gas jar
7. Quickly place lid back and shake vigorously
8. Test the solution with acid-base indicator
**Observations:**
**Chemical reactions:**
Sulfur + Oxygen (from air) → **Sulfur dioxide gas**
Sulfur dioxide + Water → **Sulfurous acid**
**Testing the nature:**
Sulfurous acid solution is **acidic in nature** (turns blue litmus paper red)
**Important difference:**
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**In air and water reactions:**
| Property | Metals (Iron, Magnesium) | Non-metals (Sulfur) |
|----------|--------------------------|---------------------|
| Oxide nature | Basic | Acidic |
| Reaction with air | Forms oxides (basic) | Forms acidic oxides |
| Reaction with water | Can react vigorously | Generally don't react |
| Heat generation | Can generate heat | May burn with heat |
| Oxide in water | Forms base | Forms acid |
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**Activity 4.8 - Sulfur with water:**
**Materials:**
**Procedure:**
1. Take sulfur powder in a glass tumbler
2. Add water to it
3. Stir and observe
**Observation:** Sulfur does NOT dissolve in water. It remains as a powder suspended in water.
**Key finding:** Unlike metals (especially sodium), sulfur does not react with water at room temperature. It is chemically inert in normal conditions.
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| Property | Metals | Non-metals |
|----------|--------|------------|
| Lustre | Lustrous (shiny) | Non-lustrous (dull) |
| Hardness | Generally hard | Variable (brittle/soft) |
| Malleability | Malleable (flatten easily) | Brittle (break) or Non-malleable |
| Ductility | Ductile (drawn into wires) | Not ductile |
| Sonority | Sonorous (ringing sound) | Not sonorous (dull sound) |
| Heat conduction | Good conductors | Poor conductors |
| Electricity conduction | Good conductors | Poor conductors |
| Oxide nature | Basic | Acidic |
| Examples | Cu, Fe, Al, Ag, Au | S, C, Coal, Wood, Sulfur |
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**Brittleness:** Property of breaking into pieces when beaten (coal, sulfur)
**Corrosion:** Gradual deterioration of metal surfaces by air, water, or other substances
**Conduction:** Transfer of heat from one point to another through a material
**Conductor:** Material that allows heat or electricity to pass through it
**Ductility:** Property of being drawn into thin wires
**Galvanisation:** Coating iron with protective zinc layer to prevent rusting
**Insulator:** Material that prevents heat or electricity from passing through
**Lustre:** Shiny or reflective appearance of metals (metallic lustre)
**Malleability:** Property of being beaten into thin sheets without breaking
**Metallic lustre:** Shiny appearance characteristic of metals
**Non-metal:** Substance lacking metallic properties (usually dull, poor conductors)
**Oxide:** Compound formed when a substance combines with oxygen
**Rust:** Brown deposit formed on iron due to reaction with moist air
**Rusting:** Process of formation of rust on iron
**Silica gel:** Drying agent used to remove moisture from air
**Sonority:** Property of producing ringing sound when struck
**Sonorous:** Capable of producing ringing sound
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1. **Metals are:** lustrous, generally hard, malleable, ductile, sonorous, good conductors of heat and electricity
2. **Rusting needs BOTH:** air (oxygen) and water. Neither alone causes rusting. Moist air is the culprit.
3. **Metal oxides are basic** while **non-metal oxides are acidic**
4. **Good heat conductors:** All metals (use metal vessels for cooking)
5. **Heat insulators:** Wood, plastic, rubber (use these for handles)
6. **Good electricity conductors:** All metals (protect from electric shock with insulators)
7. **Prevent rusting by:** painting, oiling, greasing, or galvanisation
8. **Most malleable metals:** Gold and silver
9. **Most ductile metal:** Gold (can make 2 km wire from 1 gram)
10. **Most sonorous metals:** Copper and iron (bells, musical instruments)
11. **Exceptions to metal properties:** Sodium (soft), Mercury (liquid at room temperature)
12. **Iron Pillar of Delhi:** 1600 years old, barely rusted, shows ancient Indian metallurgical skill
13. **Magnesium burns** with white flame to form basic magnesium oxide
14. **Sulfur burns** to form acidic sulfur dioxide, which dissolves in water to make sulfurous acid
15. **Sulfur does NOT react** with water at room temperature (unlike sodium)
Q1. Which of the following is a property of metals?
Answer: A — Metals are shiny (lustrous) and are good conductors of both heat and electricity, while non-metals are dull and brittle.
Q2. What happens when a piece of copper is beaten with a hammer?
Answer: B — Copper is malleable, so it can be beaten into thin sheets without breaking, which is why thin copper foils can be made.
Q3. Which material would be best for making the handle of a cooking pot?
Answer: C — Wood and plastic are poor conductors of heat, so they protect hands from burns, while metal handles would conduct heat and burn hands.
Q4. What is the property by which metals can be drawn into wires?
Answer: B — Ductility is the specific property that allows metals to be stretched and drawn into wires used in electrical fittings and instruments like sitar.
Q5. In Activity 4.3, why did the metal spoon get hotter than the wooden spoon?
Answer: B — Metals conduct heat rapidly from hot water through the spoon, while wood conducts heat poorly, remaining cooler longer.
Q6. Why does Sudarshan heat iron before beating it into an axe?
Answer: B — Heating iron increases its malleability, making it easier to beat and shape into desired forms like axes and tools without breaking.
Q7. Which of the following materials would make the bulb glow in an electrical tester circuit?
Answer: C — Copper and iron are metals that are good conductors of electricity and allow current to flow, making the bulb glow in the tester.
Q8. A suspension bridge uses steel wire ropes instead of wooden ropes because steel is—
Answer: C — Steel is ductile (can be drawn into wires) and strong, making it capable of supporting the heavy loads of bridges and cranes.
Q9. Why did Sudarshan need to use coal in his furnace to heat the iron?
Answer: B — Coal burns to produce high heat that makes iron hot and malleable, allowing the ironsmith to beat and shape it into useful tools and utensils.
Q10. An iron nail develops a brown deposit when left in the open for several days because—
Answer: C — Rust forms only when iron is exposed to both oxygen in air and water (moisture) simultaneously; either one alone does not cause rusting.
What is malleability?
The property of metals by which they can be beaten into thin sheets without breaking.
Define ductility with an example.
The property of metals to be drawn into wires; copper wires in electrical fittings show ductility.
What is sonority?
The property of metals to produce a ringing sound when struck or dropped.
Why are cooking vessel handles made of wood instead of metal?
Wood is a poor conductor of heat, so it protects hands from burns while metal vessel conducts heat.
Why does an electrician wear rubber gloves?
Rubber is a poor conductor of electricity and prevents electric shock by not allowing current to flow.
What is the difference between a conductor and an insulator?
A conductor allows heat or electricity to flow through it easily; an insulator prevents or slows down this flow.
Name one metal that is liquid at room temperature.
Mercury is the only metal that is liquid at room temperature and is used in thermometers.
What conditions cause iron to rust?
Iron rusts when it comes into contact with both air and water together, not just one alone.
What is the brown deposit that forms on iron objects called?
The brown deposit is called rust, which forms due to corrosion of iron in presence of air and moisture.
Which metal is the most malleable and ductile?
Gold is the most malleable and ductile metal; one gram can be drawn into 2 kilometre-long wire.
What is malleability? Give one example. [1 mark]
Define as ability to be beaten into sheets. Example: copper foil, aluminium foil, or gold foil used for wrapping food or sweets.
Explain why metal cooking vessels have wooden or plastic handles. What property of materials is involved? [2 marks]
Metals conduct heat (good conductors), wood and plastic do not conduct heat (poor conductors). This protects hands from burns.
In Activity 4.1, why did the copper piece flatten when hammered but the coal lump broke into pieces? Name the properties involved. [3 marks]
Copper is malleable (flattens when beaten). Coal is brittle (breaks into pieces when beaten). Explain that metals are malleable while non-metals are brittle and cannot be shaped by beating.
Describe Activity 4.3 to show that metals are good conductors of heat. What can you conclude about using metals for cooking vessels? Draw and label a diagram of the experimental setup. [5 marks]
Diagram: glass tumbler with hot water, metal spoon and wooden spoon immersed. Observation: metal spoon becomes hotter. Conclusion: metals conduct heat quickly, so they are suitable for cooking. Wood is poor conductor, making handles safe.
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