Chapter 3: Metals and Non-metals

Science · CBSE Class 10 · NCERT Solutions

📖 Chapter 3 — Metals and Non-metals (CBSE Class 10 Science): Detailed notes — physical & chemical properties, reactivity series, ionic bonding, metallurgy, corrosion.

Chapter 3 — Metals and Non-metals

🔍 1. Physical Properties

Property	Metals	Non-metals
Lustre	Shiny	Dull (except iodine, diamond)
Malleability/Ductility	Malleable & ductile	Brittle
Conductivity	Good (heat/electricity)	Poor (except graphite)
Sonority	Sonorous	Not sonorous
State/M.P.	Solid, high (exc. Hg liquid; Na/K soft)	Solid/liquid/gas, low

⚗️ 2. Chemical Properties

With O₂: Metal → basic oxide (Na₂O, MgO) ; Non-metal → acidic oxide. Amphoteric oxides (Al₂O₃, ZnO) react with both acids and bases.
With water: K, Na react violently (cold water); Mg with hot; Fe with steam; Cu/Ag/Au — no reaction.
With acids: Metal + dilute acid → salt + H₂↑ (Cu, Ag, Au do not react).
With salt solutions: more reactive metal displaces less reactive (Fe + CuSO₄ → FeSO₄ + Cu).

📶 3. Reactivity Series

K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > Au (most → least reactive)

🔗 4. Ionic (Electrovalent) Bonding

Metal loses electron(s) → cation (Na⁺); non-metal gains → anion (Cl⁻); attraction forms an ionic compound (Na⁺Cl⁻). Properties: solid crystals, high melting/boiling points, soluble in water, conduct electricity in molten/aqueous state.

⛏️ 5. Metallurgy (Extraction)

Minerals/Ores: ore = mineral with high metal content, economical to extract.
Enrichment of ore → Roasting (sulphide ore →oxide, with air) / Calcination (carbonate ore →oxide, without air) → Reduction (oxide → metal, using C for moderately reactive metals; electrolysis for reactive K, Na, Ca, Mg, Al).
Refining: electrolytic refining (anode = impure metal, cathode = pure metal, electrolyte = metal-salt solution).

🛡️ 6. Corrosion & Alloys

Corrosion: iron rusts (needs air + water), silver blackens, copper turns green. Prevented by painting, oiling, galvanising (zinc coat), alloying, electroplating. Alloys: steel (Fe+C), stainless steel (Fe+Cr+Ni), brass (Cu+Zn), bronze (Cu+Sn), solder (Pb+Sn); amalgam contains mercury.

🧠 Remember: Amphoteric = Al₂O₃, ZnO. Roasting=sulphide, Calcination=carbonate. Reactive metals (K,Na,Ca,Mg,Al) → electrolysis. Na/K under oil. Food cans → tin (not zinc, zinc more reactive).

⭐ Exam Tips: ① Physical property table + exceptions. ② Reactions (O₂/water/acid/salt). ③ Reactivity series. ④ Ionic compound properties. ⑤ Roasting vs calcination, electrolytic refining. ⑥ Corrosion prevention, alloys.

📘 Textbook Question Answers

Q1-4MCQs: displacement pair; rust prevention; oxide element; food cans.

Q1: (d) AgNO₃ + copper (Cu is more reactive than Ag). Q2: (d) All of the above. Q3: (a) calcium (CaO — high m.p., soluble giving Ca(OH)₂). Q4: (c) zinc is more reactive than tin (would react with food acids).

Q5Using hammer, battery, bulb — distinguish metals from non-metals.

(a) Malleability test: hammer the sample — metals flatten into sheets, non-metals break. Conductivity test: put the sample in a battery-bulb circuit — the bulb glows for metals (conductors), not for non-metals. (b) Useful in most cases, but not fully reliable — graphite (non-metal) conducts, and some metals are brittle.

Q6-7Amphoteric oxides; metals that displace H₂ and those that don't.

Q6: Amphoteric oxides react with both acids and bases. Examples: Al₂O₃, ZnO. Q7: Displace H₂ from dilute acids: Mg, Zn (also Fe, Al). Do not: Cu, Ag (also Au).

Q8Electrolytic refining — anode, cathode, electrolyte for metal M.

Anode: impure metal M. Cathode: a thin strip of pure metal M. Electrolyte: a solution of a salt of the metal M.

Q9Sulphur heated → gas; action on litmus; equation.

The gas is SO₂. (a)(i) No action on dry litmus paper. (ii) Turns moist blue litmus red (SO₂ is acidic). (b) S + O₂ → SO₂.

Q10-11Two ways to prevent rusting; oxides formed by non-metals + O₂.

Q10: Painting/greasing and galvanising (zinc coating). Q11: Non-metals form acidic (or neutral) oxides (e.g., CO₂, SO₂).

Q12Give reasons (jewellery; Na/K under oil; Al utensils; oxide conversion).

(a) Pt, Au, Ag are lustrous and non-reactive (don't corrode), so used for jewellery. (b) Na, K, Li are very reactive — they catch fire with air/moisture — so stored under oil. (c) Al forms a protective oxide layer that prevents further reaction, so it is safe for cooking utensils. (d) It is easier to reduce oxides to metal than carbonates/sulphides, so they are first converted to oxides.

Q13-14Cleaning tarnished copper with lemon; metal vs non-metal (chemical).

Q13: The tarnish is basic copper oxide/carbonate; the acids in lemon/tamarind (citric/tartaric) dissolve it, restoring shine. Q14: Metals form basic oxides, lose electrons (electropositive), displace H₂ from acids, act as reducing agents. Non-metals form acidic oxides, gain electrons (electronegative), do not displace H₂, act as oxidising agents.

Q15-16Goldsmith story — what solution reduced the gold's weight?

He dipped the bangles in aqua regia (a 3:1 mixture of concentrated HCl and HNO₃), which dissolves gold. The outer layer of gold dissolved, giving a shine but reducing the weight.

Extra practice (4× the textbook) — MCQ, short answer, long answer & equations.

🎯 Extra MCQ

1Which metal reacts with cold water?

Sodium/Potassium (very reactive).

2The most ductile metal is —

Gold (also silver).

3Which oxide is neither acidic nor basic?

Neutral oxides like H₂O, CO, N₂O.

4Thermite reaction uses which metal as reducing agent?

Aluminium (Fe₂O₃ + 2Al → 2Fe + Al₂O₃).

📝 Short Answer

5Why is sodium kept immersed in kerosene oil?

It reacts vigorously with air and water (catches fire); oil prevents contact with them.

6What is an alloy? Why are alloys used?

A homogeneous mixture of metals (or metal + non-metal). Alloys have better properties — more strength, resistance to corrosion, etc.

7Why does aluminium not corrode easily?

It forms a thin, tough oxide layer (Al₂O₃) that protects the metal underneath.

8Define roasting and calcination.

Roasting: heating a sulphide ore strongly in air to form its oxide. Calcination: heating a carbonate ore in limited air to form its oxide.

9Why is copper used for making electric wires?

It is a very good conductor of electricity and is ductile.

⚗️ Equations

10Reaction of sodium with water.

2Na + 2H₂O → 2NaOH + H₂↑ (+ heat).

11Reaction of zinc with dilute sulphuric acid.

Zn + H₂SO₄ → ZnSO₄ + H₂↑.

12Reaction of aluminium oxide with NaOH (amphoteric).

Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O.

📖 Long Answer

13Explain the extraction of a metal of medium reactivity (e.g., zinc).

The ore is enriched, then roasted (ZnS → ZnO) or calcined (ZnCO₃ → ZnO), and the oxide is reduced with carbon: ZnO + C → Zn + CO. The metal is then purified by electrolytic refining.

14How does an ionic bond form in NaCl? List its properties.

Na loses one electron to become Na⁺; Cl gains it to become Cl⁻; opposite charges attract to form Na⁺Cl⁻. Properties: solid crystals, high melting point, soluble in water, conduct electricity when molten or dissolved.

15Explain corrosion and four methods to prevent it.

Corrosion is the slow eating of a metal surface by air/moisture (rusting of iron). Prevention: (1) painting/greasing, (2) galvanisation (zinc coating), (3) electroplating, (4) alloying (e.g., stainless steel).