Chapter 4 – The World of Metals and Non-metals

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4.1 Properties of Materials

Activity 4.1 – Table 4.1: “Are they lustrous? Hard or soft? What happens when hammered?”

S. No. Object / material Appearance Hard / soft Effect of hammering
1 Piece of copper Shiny (lustrous) Hard Flattens into a thin sheet
2 Piece of aluminium Shiny (lustrous) Hard Flattens into a thin sheet
3 Iron nail Shiny grey (lustrous) Hard Flattens slightly
4 Lump of sulfur Dull yellow (non-lustrous) Soft & brittle Breaks into powder
5 Piece of coal Dull black (non-lustrous) Brittle Breaks into pieces
6 Block of wood Dull brown (non-lustrous) Hard-ish Neither flattens nor breaks

Which objects did you find become flat on beating with a hammer?

The copper piece, aluminium piece and iron nail all became flatter; these three are metals and are malleable.

Can we do this with other metals as well?

Yes. Most metals (gold, silver, tin, zinc, etc.) can be hammered into sheets because malleability is a common metal property.

Can you give some examples of metal sheets?

  • Thin aluminium foil used to wrap food.

  • Silver foil on Indian sweets.

  • Steel sheets used for car bodies.

  • Corrugated iron sheets for roofs.

What could be the potential reason that it is generally considered that copper was discovered earlier as compared to iron?

Copper melts at a much lower temperature and is found in nature mainly as colourful surface ores, so ancient people could spot and smelt it in open fires. Iron needs a much hotter furnace and its ores look like ordinary stones, so it was mastered later.

4.1.2 Ductility

Where do you find the use of metal wires?

In electric wiring, fences, musical-instrument strings, bicycle spokes, jewellery chains and steel ropes on bridges and cranes.

4.1.3 Sonority

Do you notice any difference in the sound produced by these objects?

Yes. Metal objects (spoon, coin) give a clear ringing sound, while coal and wood give a dull thud. This ringing property is called sonority and belongs to metals.

4.1.4 Conduction of Heat

Which of the spoons gets hotter?

The metal spoon becomes noticeably hotter.

What does this experiment tell us about heat transfer along the two spoons?

Heat travels quickly through metal but very slowly through wood. Metals are good conductors of heat; wood is a poor conductor.

4.1.5 Conduction of Electricity – Activity 4.4 (Table 4.2)

S. No. Object / material Bulb glows? Good or poor conductor
1 Aluminium foil Yes Good conductor
2 Iron nail Yes Good conductor
3 Copper wire Yes Good conductor
4 Lump of sulfur No Poor conductor
5 Piece of coal No Poor conductor
6 Dry wood piece No Poor conductor
7 Stone No Poor conductor
8 Rubber eraser No Poor conductor
9 Nylon rope piece No Poor conductor

Pattern noticed: All materials that let the bulb glow are metals.

4.2 Rusting of Iron

In which conditions would an iron object develop brown deposits?

Only when it is in contact with both air and water together (moist air).

What can you conclude from this experiment?

Rust forms only when iron has both water and oxygen. Dry air alone or water alone does not rust iron.

What does this observation indicate?

It shows that moist air (air + water) is the real cause of the brown rust on iron.

4.3 Effect of Air on Magnesium

What do you observe?

The burning magnesium ribbon gives a very bright white flame and leaves behind a fluffy white ash (magnesium oxide).

Is the solution of magnesium oxide acidic, basic or neutral? What does it do to litmus?

It is basic. It turns red litmus blue and leaves blue litmus unchanged.

Can you predict the nature of sodium oxide?

Yes. Like magnesium oxide, sodium oxide is also basic.

4.4 Burning Sulfur

What do you observe?

Sulfur burns with a pale blue flame and forms a gas with a sharp smell. The gas solution is acidic (turns blue litmus red).

Does sulfur behave in water the same way metals do?

No. Sulfur does not react with or dissolve in cold water.

Activity 4.8 – What do you observe?

The sulfur powder just sinks and nothing happens—no heat, no fizz, no colour change.

4.5 Non-metals in Life

Can you think of any other uses of oxygen?

  • Hospitals give oxygen cylinders to patients.

  • Oxygen is used in welding torches.

  • It helps steel-making furnaces burn hotter.

  • Astronauts and divers carry oxygen tanks.

LET US ENHANCE OUR LEARNING (Exercises)

1. Metal used for cheap foldable food-packs

(i) Aluminium

2. Metal that catches fire on contact with water

(iv) Sodium

3. True / False

Statement True / False Reason
(i) Aluminium and copper are non-metals False – both are metals.
(ii) Metal oxides turn blue litmus red False – metal-oxide solutions are usually basic, so they turn red litmus blue.
(iii) Oxygen is a non-metal essential for respiration True – we breathe it in.
(iv) Copper vessels are used for boiling water because they are good conductors of electricity False – They are chosen mainly for good heat conduction.

4. Why are only a few metals suitable for jewellery?

Jewellery needs metals that are shiny, do not rust, are easily shaped, and do not hurt the skin. Only a few metals—mainly gold, silver and platinum—meet all these requirements.

5. Match the uses (Column I) with metals / non-metals (Column II)

Column I (Use) Letter Correct name
(i) Used in electrical wiring (c) P E P O R C COPPER
(ii) Most malleable and ductile (e) O G D L GOLD
(iii) Living organisms cannot survive without it (a) E N X Y G O OXYGEN
(iv) Makes plants grow healthy in fertilisers (d) T E N G O I N R NITROGEN
(v) Used in water purification (b) N E C O H I R L CHLORINE

6. What happens when oxygen reacts with magnesium and sulfur?

  • Magnesium + oxygen → magnesium oxide (a white solid, basic).

  • Sulfur + oxygen → sulfur dioxide gas → with water gives sulfurous acid (acidic).
    So the metal oxide is basic, the non-metal oxide is acidic.

7. Complete the flow chart

sql
Substance ➜ Air + Heat ➜ Ash / oxide ➜ Add water ➜ Test with litmus
Magnesium ✔ White ash Basic Turns red litmus blue
Sulfur ✔ Gas, dissolves Acidic Turns blue litmus red

(Blue litmus stays blue for magnesium oxide; red litmus turns blue.
Blue litmus turns red for sulfurous solution; red litmus stays red.)

8. Best material to make a pan for boiling water? Why?

Copper is the best: it conducts heat very fast, is strong enough for a pan, and does not react dangerously with water. Non-metals like sulfur, coal, plastic, wood or cardboard cannot stand heat or flames.

9. Three iron nails dipped in oil, water and vinegar – which will not rust and why?

The nail kept in oil will not rust because the oil keeps out both air and water, so no moisture reaches the iron.

10. How do different properties decide the uses of metals and non-metals?

  • Metals are shiny, strong, malleable, ductile and conduct heat & electricity, so we use them in pots, wires, machines, vehicles.

  • Non-metals can be gases or brittle solids and often form acids or essential chemicals, so we use them for breathing (oxygen), fertilisers (nitrogen), antiseptics (iodine), water-cleaning (chlorine).

11. Could sulfur coating protect iron from rust like zinc does? Why / why not?

No. Sulfur does not stick as a tough metal layer and it is brittle. It would crack and fall off, letting moisture reach the iron. Zinc works because it is a reactive metal that forms a tight, protective coat (galvanising).

12. Why does an ironsmith heat iron before making tools?

Heating makes iron softer and easier to bend or hammer, so the smith can shape it into spades, axes, etc., before it cools and hardens again.

Other short in-text questions

Question Simple answer
“Can you predict the nature of its (sodium) oxide?” Sodium oxide is basic.
“Do you know why screw-driver handles are plastic and electricians wear rubber gloves?” Because plastic and rubber do NOT conduct electricity, so they protect against shocks.
“Can we do this with other metals as well?” Yes, most metals can be shaped when hammered or rolled.
“Have you ever noticed the formation of a green coating on copper or black on silver?” These coatings are also corrosion products like rust.

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