Class 10 › Science › Chapter 3
Metals and Non-metals
Physical and chemical properties of metals and non-metals, the reactivity series, ionic compounds, extraction and refining of metals, corrosion and alloys.
1. Physical Properties of Metals and Non-metals
| Property | Metals | Non-metals |
|---|---|---|
| Lustre | Shining surface in pure state (metallic lustre) | Dull |
| Hardness | Generally hard | Generally soft |
| Malleability | Can be beaten into sheets (gold and silver the most malleable) | Not malleable (brittle) |
| Ductility | Can be drawn into wires (gold the most ductile: ~2 km wire from 1 g) | Not ductile |
| Heat conduction | Good; high melting points. Best: silver and copper; lead and mercury are poor | Bad conductors |
| Electrical conduction | Good conductors | Bad conductors |
| Sonority | Sonorous (ring when struck; school bells) | Not sonorous |
| State at room temp. | Solids, except mercury (liquid) | Solids or gases, except bromine (liquid) |
Exceptions
Metals
Gallium and caesium melt on your palm. Lithium, sodium, potassium are soft enough to cut with a knife, with low density and low melting points.
Exceptions
Non-metals
Iodine is lustrous. Diamond (allotrope of carbon) is the hardest natural substance with very high melting and boiling points. Graphite conducts electricity.
- Allotropes: different forms of the same element (diamond, graphite).
- Physical properties alone cannot classify elements because of exceptions, so chemical properties are used.
- Electric wires are coated with PVC or rubber because these are insulators.
2. Chemical Properties: Reaction with Oxygen
Metal + OxygenMetal + Oxygen → Metal oxide (basic in nature)
2Cu + O2 → 2CuOCopper(II) oxide is black.
4Al + 3O2 → 2Al2O3
Amphoteric oxides: metal oxides that react with both acids and bases to give salt and water. Examples: Al2O3 and ZnO.
Al2O3 + 6HCl → 2AlCl3 + 3H2O
Al2O3 + 2NaOH → 2NaAlO2 + H2OSodium aluminate.
- Most metal oxides are insoluble in water; Na2O and K2O dissolve to form alkalis: Na2O(s) + H2O(l) → 2NaOH(aq).
- Non-metal oxides are acidic (or neutral). Burn Mg: its ash turns red litmus blue (basic). Burn S: SO2 dissolves in water and turns blue litmus red (acidic).
- Reactivity with oxygen varies: K and Na catch fire in air, so they are kept under kerosene oil. Mg, Al, Zn, Pb get a thin protective oxide layer. Iron does not burn on heating, but iron filings burn vigorously. Copper forms black CuO on heating. Silver and gold do not react with oxygen even at high temperatures.
Do You Know? Anodising
A thick oxide layer is formed on aluminium by making a clean aluminium article the anode and electrolysing dilute sulphuric acid. The oxygen released at the anode thickens the protective layer, which can also be dyed.
3. Reaction with Water
GeneralMetal + Water → Metal oxide + H2; Metal oxide + Water → Metal hydroxide
| Metal | Condition | Reaction |
|---|---|---|
| K, Na | Cold water; violent | 2K + 2H2O → 2KOH + H2 + heat 2Na + 2H2O → 2NaOH + H2 + heat Heat is enough for H2 to catch fire. |
| Ca | Cold water; less violent | Ca + 2H2O → Ca(OH)2 + H2 Ca floats as H2 bubbles stick to it; no fire. |
| Mg | Hot water only | Forms Mg(OH)2 and H2; also floats. |
| Al, Fe, Zn | Steam only | 2Al + 3H2O(g) → Al2O3 + 3H2 3Fe + 4H2O(g) → Fe3O4 + 4H2 |
| Pb, Cu, Ag, Au | No reaction with water at all | - |
4. Reaction with Acids
Metal + Dilute acidMetal + Dilute acid → Salt + Hydrogen
Mg + 2HCl → MgCl2 + H2 | 2Al + 6HCl → 2AlCl3 + 3H2
Zn + 2HCl → ZnCl2 + H2 | Fe + 2HCl → FeCl2 + H2
- Rate of bubbling and heat released: Mg is fastest and most exothermic; order Mg > Al > Zn > Fe. Copper does not react with dilute HCl.
- Nitric acid does not give H2: HNO3 is a strong oxidising agent that oxidises H2 to water and is itself reduced to nitrogen oxides (N2O, NO, NO2). Only Mg and Mn give H2 with very dilute HNO3.
- Aqua regia (3 parts conc. HCl : 1 part conc. HNO3) dissolves gold and platinum.
5. Reaction with Solutions of Other Metal Salts
DisplacementMetal A + Salt solution of B → Salt solution of A + Metal B
Fe + CuSO4 → FeSO4 + CuIron nail in CuSO4: the blue colour fades and copper coats the nail. Copper wire in FeSO4: no reaction.
- A more reactive metal displaces a less reactive metal from its salt solution or molten salt. So Fe is more reactive than Cu.
- Zinc added to iron(II) sulphate displaces iron: Zn + FeSO4 → ZnSO4 + Fe.
6. The Reactivity (Activity) Series
Reactivity series: a list of metals arranged in order of decreasing reactivity.
K > Na > Ca > Mg > Al > Zn > Fe > Pb > [H] > Cu > Hg > Ag > AuPotassium is most reactive; gold is least reactive.
- Metals above hydrogen displace H2 from dilute acids.
- Displacement reactions (Act. 1.9 and 3.12) give the best evidence for the order.
- Aluminium is highly reactive but is used for cooking utensils because its protective oxide layer prevents further corrosion.
7. How Metals and Non-metals React: Ionic Bonding
- Noble gases have a completely filled valence shell and show little chemical activity. Other elements react to attain a filled valence shell (octet).
- Metals lose electrons to form positive ions (cations); non-metals gain electrons to form negative ions (anions).
Formation of NaCl
Na (2,8,1) → Na+ (2,8) + e−: sodium loses 1 electron to get a stable octet.
Cl (2,8,7) + e− → Cl− (2,8,8): chlorine gains 1 electron.
The oppositely charged ions attract by strong electrostatic force to form NaCl. NaCl exists as an aggregate of ions, not molecules.
Mg (2,8,2) → Mg2+ (2,8) + 2e− | 2Cl + 2e− → 2Cl−MgCl2: cation Mg2+, anion Cl−, ratio 1 : 2.
Ionic (electrovalent) compound: a compound formed by transfer of electrons from a metal to a non-metal.
8. Properties of Ionic Compounds
Physical nature
Hard, brittle solids
Strong attraction between ions makes them somewhat hard; they break into pieces under pressure.
Melting / boiling
High
Large energy is needed to break strong inter-ionic attraction. Example: NaCl m.p. 1074 K, b.p. 1686 K.
Solubility
Soluble in water
Generally insoluble in kerosene, petrol, etc.
Conduction
Molten or dissolved only
Solid: no (ions cannot move in the rigid structure). Solution or molten: yes (ions move freely).
9. Occurrence and Extraction of Metals
Mineral
Naturally occurring
Elements or compounds found in the earth's crust.
Ore
Metal can be profitably extracted
A mineral with a very high percentage of the metal.
Gangue
Impurities in ore
Soil, sand, etc., removed before extraction (enrichment).
| Group (by reactivity) | Occurrence | Method |
|---|---|---|
| Low: Ag, Au (Hg, Cu) | Free state (Au, Ag, Pt, Cu); Cu and Hg also as sulphide or oxide ores | Roasting of sulphide, then heating oxide alone |
| Medium: Zn, Fe, Pb, etc. | Oxides, sulphides, carbonates | Convert to oxide, then reduce with carbon (or by displacement) |
| High: K, Na, Ca, Mg, Al | Never free | Electrolytic reduction of molten compound |
Low reactivity metals: heat alone
Mercury: 2HgS + 3O2 → 2HgO + 2SO2 (heat), then 2HgO → 2Hg + O2 (heat). Ore: cinnabar (HgS).
Copper: 2Cu2S + 3O2 → 2Cu2O + 2SO2, then 2Cu2O + Cu2S → 6Cu + SO2.
Medium reactivity metals: oxide, then reduction
Roasting (sulphide ore, heat strongly in excess air): 2ZnS + 3O2 → 2ZnO + 2SO2.
Calcination (carbonate ore, heat strongly in limited air): ZnCO3 → ZnO + CO2.
Reduction with carbon: ZnO + C → Zn + CO. Oxides are easier to reduce than sulphides or carbonates, which is why ores are first converted to oxides.
Displacement: highly reactive Na, Ca, Al act as reducing agents. 3MnO2 + 4Al → 3Mn + 2Al2O3 + heat (MnO2 is reduced, Al is oxidised).
Thermit reaction: Fe2O3 + 2Al → 2Fe(l) + Al2O3 + heat. The molten iron joins railway tracks and cracked machine parts.
High reactivity metals: electrolysis
Carbon cannot reduce oxides of Na, Mg, Ca, Al because these metals have more affinity for oxygen than carbon does.
Electrolyse the molten chloride (e.g. NaCl). Cathode (−): Na+ + e− → Na. Anode (+): 2Cl− → Cl2 + 2e−. Aluminium is obtained by electrolytic reduction of Al2O3.
10. Refining of Metals: Electrolytic Refining
Anode (+)
Impure metal
Dissolves into the electrolyte.
Cathode (−)
Thin strip of pure metal
Pure metal is deposited here.
Electrolyte
Solution of metal salt
For copper: acidified copper sulphate.
- Soluble impurities stay in solution; insoluble impurities settle below the anode as anode mud.
- Used for copper, zinc, tin, nickel, silver, gold, etc.
11. Corrosion, its Prevention and Alloys
Silver
Black coating
Silver reacts with sulphur in air to form silver sulphide.
Copper
Green coating
Reacts with moist CO2 to form basic copper carbonate.
Iron
Rust
Brown flaky coating on exposure to moist air. Rusting needs both air and water (Act. 3.14).
- Prevention of rusting: painting, oiling, greasing, galvanising, chrome plating, anodising, making alloys.
- Galvanisation: coating iron or steel with zinc. It protects even when the coating is broken, since zinc is more reactive than iron and corrodes first.
Alloy: a homogeneous mixture of two or more metals, or a metal and a non-metal. Made by melting the main metal, dissolving the other elements in definite proportions, then cooling.
| Alloy | Made of | Note |
|---|---|---|
| Steel | Iron + ~0.05% carbon | Pure iron is soft and stretches when hot; carbon makes it hard and strong |
| Stainless steel | Iron + nickel + chromium | Hard and does not rust |
| Brass | Copper + zinc | Poor electrical conductor |
| Bronze | Copper + tin | Poor electrical conductor |
| Solder | Lead + tin | Low melting point; welds electrical wires |
| Amalgam | Any alloy containing mercury | - |
- Alloys have lower electrical conductivity and melting point than the pure metals.
- 22 carat gold: 22 parts pure gold + 2 parts copper or silver. Pure 24 carat gold is too soft for jewellery.
- Delhi iron pillar (over 1600 years old, 8 m high, ~6 tonnes) is famous for its rust resistance.
12. Quick Revision
| Topic | Remember |
|---|---|
| Metal oxides | Basic; Al2O3 and ZnO are amphoteric |
| Non-metal oxides | Acidic or neutral |
| Metals + dilute acid | Salt + H2 (only metals above hydrogen) |
| Non-metals | Do not displace H2 from acids; react with hydrogen to form hydrides |
| Metal + non-metal | Metal loses electrons, non-metal gains: ionic bond |
| Roasting vs calcination | Sulphide, excess air vs carbonate, limited air |
| Extraction | Top: electrolysis; middle: carbon reduction; bottom: heat alone / native |
| Electrolytic refining | Impure anode, pure cathode, metal salt electrolyte |
Common mistakes:
• Saying all metals are solid; mercury is a liquid, and Na, K, Li are soft.
• Saying all non-metals are brittle, dull and non-conducting; graphite conducts and iodine is lustrous.
• Mixing up roasting (sulphide, excess air) and calcination (carbonate, limited air).
• Expecting H2 from nitric acid reactions.
• Thinking ionic compounds conduct as solids; they conduct only when molten or dissolved.
• Writing the reactivity series in the wrong order: remember K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au.
• Forgetting that rusting needs both air and water.
• Saying all metals are solid; mercury is a liquid, and Na, K, Li are soft.
• Saying all non-metals are brittle, dull and non-conducting; graphite conducts and iodine is lustrous.
• Mixing up roasting (sulphide, excess air) and calcination (carbonate, limited air).
• Expecting H2 from nitric acid reactions.
• Thinking ionic compounds conduct as solids; they conduct only when molten or dissolved.
• Writing the reactivity series in the wrong order: remember K, Na, Ca, Mg, Al, Zn, Fe, Pb, H, Cu, Hg, Ag, Au.
• Forgetting that rusting needs both air and water.