Chapter 4: The World of Metals & Non-metals
Properties • Reactions with Air/Water • Oxides • Corrosion • Everyday Uses • Safety
🔩 Metals • 🧪 Reactions • 🧯 Safety • 🌍 Applications
🗝️20 Most-Important Words (Meanings in Simple Hindi)
| Word | Meaning (Hindi) |
|---|---|
| Metal | चमकीला, कड़ा पदार्थ जो गर्मी/बिजली अच्छी तरह पहुँचाता है। |
| Non-metal | आम तौर पर धुंधला, नरम/भंगुर, गर्मी/बिजली का कमजोर वाहक। |
| Metallic lustre | धातु जैसा चमकदार रूप। |
| Malleability | हथौड़े से पीटकर पतली चादर बनाने की क्षमता। |
| Ductility | खींचकर तार बनाने की क्षमता। |
| Sonority | धारदार/घंटी जैसी बजने वाली ध्वनि पैदा करने का गुण। |
| Heat conductor | जो गर्मी को आसानी से आगे बढ़ाए (जैसे तांबा, एल्युमिनियम)। |
| Electrical conductor | जो बिजली को आसानी से बहने दे (जैसे धातुएँ)। |
| Insulator | जो गर्मी/बिजली के प्रवाह को रोके (जैसे प्लास्टिक, रबर, लकड़ी)। |
| Brittleness | पीटने पर टूट जाना, चादर न बन पाना (जैसे गंधक, कोयला)। |
| Alloy | दो या अधिक धातुओं/धातु-अधातु का मिश्रण। |
| Corrosion | हवा/पानी आदि से धातु की सतह का धीरे-धीरे खराब होना। |
| Rust | लोहे पर नम हवा से बनने वाली भूरी परत। |
| Galvanisation | लोहे पर जस्ता की पतली परत चढ़ाकर जंग से बचाना। |
| Oxide | ऑक्सीजन से मिलकर बना यौगिक (जैसे मैग्नीशियम ऑक्साइड)। |
| Basic oxide | धातु का ऑक्साइड जो क्षारीय प्रकृति दिखाए। |
| Acidic oxide | अधातु का ऑक्साइड जो अम्लीय प्रकृति दिखाए। |
| Element | सबसे सरल पदार्थ, जिसे और सरल भागों में नहीं तोड़ा जा सकता। |
| Mercury | एकमात्र धातु जो कमरे के ताप पर द्रव रूप में होती है। |
| Silica gel | नमी सोखने वाला पदार्थ, वस्तुओं को सूखा रखता है। |
📚Detailed Notes — The World of Metals & Non-metals
🏭Craft & Context
Village ironsmiths (lohar) make tawa, bucket, chimta and farm tools (spade, axe, khurpi, rake). Iron is heated (often with coal fuel) and hammered to shape — showing a key metal property: malleability.
- Handles may be wood (an insulator, safer to hold when hot).
- Hammering a hot iron block into an axe illustrates “metals can be beaten into sheets/shapes”.
🧭Classifying Materials (Recall)
- Metals: lustrous (metallic shine), generally hard, malleable, ductile, sonorous; conduct heat & electricity.
- Non-metals: usually dull, not malleable/ductile, not sonorous; poor conductors; their oxides are acidic.
- Exceptions: Sodium & potassium are soft; mercury is liquid at room temperature.
🧪Key Properties of Metals & Non-metals
- Metallic lustre & hardness: Copper, aluminium, iron are shiny & hard; coal/sulfur are dull and softer.
- Malleability: Metals can be hammered into thin sheets (silver foil on sweets, aluminium foil). Coal/sulfur are brittle. Wood is neither malleable nor brittle.
- Ductility: Metals can be drawn into wires (electric wiring, jewellery, instrument strings). Gold is extremely ductile; steel ropes (iron + carbon) lift heavy loads.
- Sonority: Metals give a ringing sound (school bell, ghungroo). Wood/coal give dull thuds.
- Conduction of heat: Metals heat up quickly (cooking vessels). Handles are made of wood/plastic (poor conductors) for safety.
- Conduction of electricity: Metals (Cu, Al, Fe) allow current; non-metals like sulfur, coal, wood, rubber do not. Electrician tools have plastic/rubber grips for protection.
Safety: Our body conducts electricity. Never touch switches with wet hands; use only cells for school experiments, not mains.
🌧️Iron: Air & Water Effects — Rusting
- Experiment with three bottles:
- A: Dry air (silica gel) → no rust.
- B: Only water (boiled & cooled, oil layer prevents air) → no rust.
- C: Moist air (air + water) → brown rust forms.
- Conclusion: Both air and water are essential for rusting (iron + moist air).
- Corrosion: General surface damage of metals by air/water; e.g., copper turns green; silver turns black.
- Prevention: Painting, oiling/greasing, and galvanisation (zinc coating on iron).
🏛️Wonder of Metallurgy
Iron Pillar of Delhi (~1600+ years old) shows minimal rust — evidence of advanced ancient Indian metallurgy and protective composition/conditions.
🔥Other Metals with Air/Water
- Magnesium ribbon: burns with dazzling white flame → forms magnesium oxide (white powder).
- MgO in warm water gives a basic solution (turns red litmus blue), showing that most metal oxides are basic.
- Sodium: extremely reactive with air/water; stored in kerosene. Its oxide is expected to be basic.
🌫️Substances Behaving Differently (Non-metals)
- Sulfur: burns in air → sulfur dioxide (SO₂); dissolving in water forms sulfurous acid (solution is acidic, turns blue litmus red).
- Sulfur + water (without burning): no reaction.
- Phosphorus: catches fire in air; stored under water for safety.
🧱Elements: Building Blocks
- Elements can’t be broken into simpler substances; about 118 known.
- Metals and non-metals are two major element groups.
- Materials like plastic, glass, wood, rubber, paper are not elements; they are substances/mixtures/polymers.
🌱Why Non-metals Matter
- Oxygen: essential for breathing, combustion, medical and industrial uses.
- Carbon: backbone of life (proteins, fats, carbohydrates).
- Nitrogen: used to make fertilisers; vital for plant growth.
- Chlorine: water purification; Iodine solution: antiseptic for wounds.
🌐Science & Society
- Metals & alloys (e.g., steel, brass) are vital for utensils, tools, machines, transport, electronics, aerospace (titanium), and atomic energy (zirconium).
- India recycles large amounts of iron & aluminium — reducing waste and supporting sustainability.
🧠In a Nutshell (Quick Revision)
- Metals: generally lustrous, hard, malleable, ductile, sonorous; good conductors of heat/electricity.
- Non-metals: generally dull, not malleable/ductile/sonorous; poor conductors.
- Metal oxides are usually basic (e.g., MgO); non-metal oxides are usually acidic (e.g., SO₂ → sulfurous acid).
- Iron rusts only in moist air (air + water). Prevent with painting, oiling, galvanisation.
- Non-metals like oxygen, carbon, nitrogen, chlorine, iodine are essential in daily life.
- Elements are fundamental substances; metals & non-metals are major categories.
- Follow electrical & lab safety at all times.
Practice Pack — The World of Metals & Non-metals
One-word • Fill in the Blanks • True/False • Very Short • Short Answers
🔩🧪🔥🌧️🛡️
🎯Section 1 — One-Word Answers (10)
1) Property by which metals are beaten into sheets:
Malleability
2) Property by which metals are drawn into wires:
Ductility
3) Ringing sound producing property of metals:
Sonority
4) Shiny appearance of metals is called metallic ______:
Lustre
5) General nature of metal oxides in water:
Basic
6) General nature of non-metal oxides in water:
Acidic
7) Brown coating formed on iron in moist air:
Rust
8) Process of formation of rust on iron:
Rusting
9) Zinc coating on iron to prevent rusting is called:
Galvanisation
10) Only liquid metal at room temperature:
Mercury
🧩Section 2 — Fill in the Blanks (10)
| Question | Answer |
|---|---|
| 1) Gold and silver are the most ______ metals. | malleable |
| 2) Metals are generally good ______ of heat and electricity. | conductors |
| 3) Non-metals are usually ______ in appearance. | dull (non-lustrous) |
| 4) Magnesium ribbon burns with a ______ white flame. | dazzling |
| 5) Sulfur burns in air to form ______ dioxide gas. | sulfur (→ sulfur dioxide, SO₂) |
| 6) SO₂ dissolved in water forms ______ acid. | sulfurous |
| 7) Iron rusts only in the presence of both ______ and ______. | air and water (moist air) |
| 8) Highly reactive sodium metal is stored in ______. | kerosene |
| 9) Phosphorus is stored under ______ to prevent catching fire. | water |
| 10) Copper objects often develop a ______-coloured coating in air. | green |
✅Section 3 — True / False with Explanations (10)
| # | Statement | Answer | Explanation |
|---|---|---|---|
| 1 | Metals are generally dull and poor conductors. | False | Metals are typically lustrous and good conductors of heat and electricity. |
| 2 | Non-metals are malleable and ductile like metals. | False | Non-metals are neither malleable nor ductile; many are brittle or soft. |
| 3 | Metal oxides in water generally show basic nature. | True | Example: Mg burns to MgO; its solution turns red litmus blue. |
| 4 | Non-metal oxides generally show acidic nature. | True | SO₂ dissolves to sulfurous acid; turns blue litmus red. |
| 5 | Iron rusts in dry air alone. | False | Rusting needs both air and water (moist air), as shown by the bottle experiment. |
| 6 | Sulfur reacts with water the same way metals do. | False | Sulfur shows no reaction with water at room conditions; metals differ. |
| 7 | Galvanisation protects iron from rusting. | True | A thin zinc layer isolates iron from moist air and offers sacrificial protection. |
| 8 | All metals are hard solids at room temperature. | False | Mercury is liquid; sodium and potassium are very soft and cuttable. |
| 9 | Wooden or plastic handles are used because they are insulators. | True | They conduct heat poorly, protecting hands during cooking or work. |
| 10 | Steel ropes are weaker than pure iron wires. | False | Steel (iron + carbon alloy) is stronger; used in cranes and suspension bridges. |
✍️Section 4 — Very Short Answers (10) • 2–3 lines each
1) Define malleability with one example.
Malleability is the ability of a material to be beaten into thin sheets. Aluminium foil and silver varq on sweets are examples.
2) What is ductility? Give a use.
Ductility is the ability to be drawn into wires. Copper and aluminium wires are used in electrical wiring and in musical instruments.
3) Why are cooking vessels metallic but handles non-metallic?
Metals conduct heat efficiently to cook food. Handles are wood/plastic as they are poor conductors and safe to hold.
4) What is sonority? Where do you notice it?
Sonority is the ringing sound produced by metals when hit. School bells, temple bells and ghungroos show sonority.
5) Define corrosion with two examples.
Corrosion is gradual surface damage of metals by air/water. Iron rusts (brown), copper develops green coating, silver turns black.
6) State the conditions required for rusting.
Rusting of iron needs both air and water (moist air). It does not occur in dry air alone or in air-free water alone.
7) Why is sodium stored in kerosene?
Sodium reacts vigorously with oxygen and water releasing heat. Kerosene isolates it from air and moisture, preventing reaction.
8) What happens when sulfur burns in air and the gas dissolves in water?
Sulfur burns to SO₂; dissolved in water it forms sulfurous acid. The solution is acidic and turns blue litmus red.
9) Why does magnesium oxide solution turn red litmus blue?
Mg burns to magnesium oxide, a metal oxide. Its aqueous solution is basic, so it turns red litmus blue.
10) Mention two essential roles of non-metals in daily life.
Oxygen (breathing, combustion) and carbon (backbone of proteins, fats, carbohydrates). Nitrogen aids plant growth via fertilisers.
📝Section 5 — Short Answers (10) • 3–4 lines each
1) Distinguish metals and non-metals on four properties with examples.
Metals: lustrous, malleable, ductile, sonorous; good conductors (Cu, Al, Fe). Non-metals: dull, brittle/soft, not sonorous; poor conductors (S, C, P). Uses follow from these properties—wires, foils, bells vs. antiseptics, fertilisers, purification.
2) Describe the three-bottle nail experiment and its conclusion.
A: dry air (silica gel) → no rust; B: only water (air excluded by oil) → no rust; C: air + water (moist air) → rust. Conclusion: iron rusts only when both air and water are present.
3) Explain sonority with daily applications.
Sonority is the ringing sound of metals when struck. It enables loud, clear sound in bells and instruments. Wood/coal produce dull sounds and are not suited for bells.
4) How can you test whether a material is a conductor or an insulator?
Make a tester (cell + lamp + two wires). Touch the free wire ends to the material’s ends. If the lamp glows, it conducts (metals); if not, it’s an insulator (plastic, rubber, wood).
5) What is galvanisation and why is it useful?
Galvanisation is coating iron with a thin layer of zinc. It prevents contact with moist air and offers sacrificial protection, thus delaying rusting of iron objects.
6) Connect a property of metals to one use each (three examples).
Malleability → aluminium foil/utensils; Ductility → copper/aluminium wires; Conductivity → cooking pots and heat exchangers. Properties guide material selection.
7) Why are alloys often preferred over pure metals? Give one example.
Alloys offer improved strength/corrosion resistance. Steel (iron + carbon) is stronger than pure iron and is used in cranes, bridges and cables.
8) Why is phosphorus stored under water while sulfur is not?
Phosphorus ignites easily in air; storing under water prevents contact with oxygen. Sulfur does not catch fire spontaneously and is safer in air.
9) Describe magnesium’s reaction with oxygen and the nature of the product.
Magnesium burns with a dazzling white flame to form MgO (white powder). MgO in water produces a basic solution that turns red litmus blue.
10) Which metal is most suitable for an economical pan for boiling water and why?
Aluminium is commonly used: it is a good heat conductor, light, malleable, and cheaper than copper. Hence it heats water efficiently at lower cost.