Metals and Non-metals Class 10: Notes and Important Questions

Metals and Non-metals is chapter 3 of Class 10 Science. This guide follows the chapter in order: physical properties and exceptions, how metals react with oxygen, water and acids, the reactivity series, ionic bonding, how metals are extracted and refined, and how corrosion is prevented. Every key equation is included, and important questions with model answers come at the end.

Physical properties of metals

• Lustre: pure metals shine. The shine may be hidden by oxide or tarnish, which sandpaper can remove.
• Hardness: metals are generally hard, though this varies.
• Malleability: can be beaten into thin sheets. Gold and silver are the most malleable metals.
• Ductility: can be drawn into thin wires. One gram of gold can be drawn into a wire nearly 2 km long.
• Conductivity: good conductors of heat and electricity. Silver and copper are the best conductors of heat; lead and mercury are poor conductors.
• Melting point: generally high.
• Sonorous: they ring when struck, which is why bells are made of metal.

Non-metals and the exceptions

Non-metals are fewer in number: carbon, sulphur, iodine, oxygen and hydrogen are examples. They are solids or gases, except bromine, which is a liquid. Solid non-metals are brittle and not lustrous.

Carbon exists in different forms called allotropes. Diamond is the hardest natural substance and has a very high melting point. Graphite conducts electricity.

Reaction with oxygen

Metal + oxygen → metal oxide

• 2Cu + O₂ → 2CuO (black copper(II) oxide)
• Most metal oxides are basic.
• Amphoteric oxides such as Al₂O₃ and ZnO react with both acids and bases to give salt and water. Example: Al₂O₃ + 2NaOH → 2NaAlO₂ + H₂O (sodium aluminate).

How strongly they react:

• Sodium and potassium catch fire in air, so they are stored under kerosene.
• Magnesium, aluminium and zinc form a thin protective oxide layer.
• Iron does not burn on heating, but iron filings burn when sprinkled in a flame.
• Copper does not burn but gets a black oxide coating.
• Silver and gold do not react with oxygen even at high temperatures.

Reaction with water

Metal + water → metal oxide + hydrogen (a soluble oxide then forms a hydroxide).

• Sodium and potassium: react violently with cold water; the hydrogen catches fire. 2Na(s) + 2H₂O(l) → 2NaOH(aq) + H₂(g) + heat energy
• Calcium: reacts less violently; it floats because hydrogen bubbles stick to it.
• Magnesium: reacts with hot water, not cold, and also floats.
• Aluminium, iron, zinc: react only with steam. 3Fe(s) + 4H₂O(g) → Fe₃O₄(s) + 4H₂(g)
• Lead, copper, silver, gold: do not react with water at all.

Reaction with acids

Metal + dilute acid → salt + hydrogen

• Order of reactivity with dilute HCl: Mg > Al > Zn > Fe.
• Copper does not react with dilute HCl.
• Nitric acid usually gives no hydrogen, because HNO₃ is a strong oxidising agent. It oxidises the hydrogen to water and is reduced to nitrogen oxides (NO₂ or NO). Very dilute HNO₃ does give hydrogen with magnesium and manganese.
• Aqua regia ("royal water") is a freshly prepared 3:1 mixture of concentrated HCl and concentrated HNO₃. It dissolves gold and platinum.

The reactivity series and displacement

A more reactive metal displaces a less reactive metal from its salt solution.

Fe(s) + CuSO₄(aq) → FeSO₄(aq) + Cu(s)

The blue solution turns light green, and reddish-brown copper coats the iron nail.

In the reactivity series, potassium and sodium are at the top, zinc and iron in the middle, and silver and gold at the bottom. Hydrogen is included as a reference: metals above it displace hydrogen from dilute acids; metals below it (such as copper and gold) cannot.

Ionic bonding

Atoms react to get a full outer shell like a noble gas. Metals (1 to 3 outer electrons) lose electrons to form cations; non-metals (5 to 7 outer electrons) gain electrons to form anions.

• NaCl: Na loses one electron to become Na⁺; Cl gains it to become Cl⁻. The ions attract each other.
• MgCl₂: Mg (2, 8, 2) gives one electron to each of two Cl atoms (2, 8, 7). Mg²⁺ becomes 2, 8 and each Cl⁻ becomes 2, 8, 8.

Properties of ionic compounds:

1. Hard, brittle solids.
2. High melting and boiling points (strong forces between ions).
3. Soluble in water, insoluble in kerosene.
4. Conduct electricity only when molten or dissolved, because only then can the ions move.

Extraction of metals

A mineral that a metal can be extracted from profitably is an ore. The unwanted soil and sand in it is gangue, removed first (enrichment).

Low reactivity (mercury, copper): heating alone is enough.

• Cinnabar (HgS) is heated in air to form HgO, then: 2HgO(s) → 2Hg(l) + O₂(g)
• 2Cu₂S(s) + 3O₂(g) → 2Cu₂O(s) + 2SO₂(g), then 2Cu₂O(s) + Cu₂S(s) → 6Cu(s) + SO₂(g)

Middle reactivity (zinc, iron): convert the ore to an oxide, then reduce it.

• Roasting (sulphide ore, strong heat, excess air): 2ZnS(s) + 3O₂(g) → 2ZnO(s) + 2SO₂(g)
• Calcination (carbonate ore, strong heat, limited air): ZnCO₃(s) → ZnO(s) + CO₂(g)
• Reduction with carbon: ZnO(s) + C(s) → Zn(s) + CO(g)
• Thermit reaction: Fe₂O₃(s) + 2Al(s) → 2Fe(l) + Al₂O₃(s) + heat. The molten iron joins cracked railway tracks and machine parts.

High reactivity (sodium, magnesium, calcium, aluminium): carbon cannot reduce their oxides, so they are extracted by electrolysis of their molten chlorides (aluminium from aluminium oxide).

• At cathode: Na⁺ + e⁻ → Na
• At anode: 2Cl⁻ → Cl₂ + 2e⁻

Electrolytic refining

Used to purify copper, zinc, tin and gold.

• Anode: thick block of impure metal.
• Cathode: thin strip of pure metal.
• Electrolyte: a salt solution of the metal (acidified copper sulphate for copper).

Pure metal dissolves from the anode and deposits on the cathode. Soluble impurities stay in solution; insoluble ones settle below the anode as anode mud.

Corrosion and its prevention

• Iron rusts, silver turns black (silver sulphide), copper gets a green coating (basic copper carbonate).
• Rusting needs both air and water. In the three-test-tube activity, only the nail in tube A (water, open to air) rusts. Tube B (boiled water under oil, no air) and tube C (anhydrous calcium chloride, no moisture) show no rust.
• Prevention: painting, oiling, greasing, chrome plating, galvanisation (coating with zinc; zinc protects iron even when scratched, because zinc is more reactive) and alloying.

Alloys: stainless steel (iron with nickel and chromium), brass (copper and zinc), bronze (copper and tin), solder (lead and tin, low melting point, used for welding electrical wires). An alloy containing mercury is an amalgam.

Important questions with answers

1. Why are bells made of metal? Metals are sonorous; they ring when struck.

2. Name a non-metal that conducts electricity and a metal with a very low melting point. Graphite; gallium (or caesium).

3. What are amphoteric oxides? Give two examples. Oxides that react with both acids and bases to give salt and water: Al₂O₃ and ZnO.

4. Why is sodium kept under kerosene? It reacts so strongly with oxygen that it catches fire at room temperature.

5. Why do calcium and magnesium float in water? Hydrogen bubbles formed in the reaction stick to the metal.

6. Why is hydrogen not given off when most metals react with nitric acid? HNO₃ is a strong oxidising agent. It oxidises the hydrogen to water and is reduced to nitrogen oxides.

7. Metal A displaces metal B from its salt solution. Which is more reactive? Metal A.

8. Why does molten NaCl conduct electricity but solid NaCl does not? In the solid, ions are fixed. In the molten state, they can move and carry current.

9. Differentiate between roasting and calcination. Roasting heats sulphide ores strongly in excess air; calcination heats carbonate ores strongly in limited air. Both give oxides.

10. Why can't sodium be extracted by heating its oxide with carbon? Sodium has a higher affinity for oxygen than carbon has, so carbon cannot remove the oxygen.

Common mistakes to avoid

• Saying copper reacts with dilute HCl. It does not.
• Mixing up roasting (sulphide, excess air) and calcination (carbonate, limited air).
• Writing that ionic compounds conduct as solids.
• Swapping anode and cathode in refining: the impure block is the anode.
• Forgetting that rusting needs both air and water.

To practise every equation and question in this chapter, study this chapter with Joy on Learnijoy.