Notes Class 10 Science Chapter 3 Metals and Non-metals

Notes For All Chapters Science Class 10 CBSE

1. Classification of Elements

Elements are broadly classified into metals and non-metals based on their physical and chemical properties.

Metals: e.g. Iron, Copper, Aluminium, Sodium, Zinc, Gold, Silver.

Non-Metals: e.g. Carbon, Sulphur, Iodine, Oxygen, Hydrogen, etc.

2. Physical Properties

Metals

• Lustre – Shiny surface (metallic lustre).
• Malleability – Can be beaten into thin sheets (gold, silver most malleable).
• Ductility – Can be drawn into wires (gold most ductile).
• Hardness – Generally hard (except sodium, potassium, lithium – soft, cut with knife).
• Conductivity – Good conductors of heat and electricity (copper, silver best).
• Melting & Boiling points – Generally high.
  • Exceptions: Gallium, Caesium – low melting points (melt in palm).
• Sonority – Produce ringing sound (school bells).
• State – Solids at room temperature (except mercury – liquid).

Non-Metals

• Usually brittle, not lustrous (except iodine – lustrous).
• Not malleable or ductile.
• Poor conductors of heat and electricity (except graphite – good conductor).
• Exist as solids or gases; bromine is liquid.
• Lower melting and boiling points compared to metals.

3. Chemical Properties

3.1 Reaction with Oxygen

Metals form metal oxides.

• Example: 2Cu + O₂ → 2CuO (black).
• 4Al + 3O₂ → 2Al₂O₃.

Metal oxides are basic in nature.

Some are amphoteric: react with both acids and bases (e.g. Al₂O₃, ZnO).

Exceptions:

• Na₂O, K₂O dissolve in water → alkalis (NaOH, KOH).
• Mg burns with dazzling white flame.
• Ag, Au – do not react with oxygen.

3.2 Reaction with Water

• Metals + Water → Metal oxide/hydroxide + Hydrogen gas.
• Sodium, Potassium: react violently, hydrogen catches fire.
• Calcium: less violent, H₂ does not catch fire.
• Magnesium: reacts with hot water, not cold.
• Aluminium, Zinc, Iron: react with steam → oxides + hydrogen.
• Lead, Copper, Silver, Gold: no reaction.

3.3 Reaction with Acids

Metals + Dilute acid → Salt + Hydrogen.

• Example: Zn + 2HCl → ZnCl₂ + H₂.

Order of reactivity: Mg > Al > Zn > Fe.

Copper does not react with dilute HCl.

Exception: Nitric acid (HNO₃) does not give H₂ (strong oxidising agent).

Aqua regia (3 parts HCl + 1 part HNO₃) dissolves gold & platinum.

3.4 Reaction with Salt Solutions (Displacement)

More reactive metal displaces less reactive metal.

Fe + CuSO₄ → FeSO₄ + Cu.

Basis of Reactivity Series:

• Most reactive: K, Na, Ca.
• Moderately reactive: Al, Zn, Fe, Pb.
• Less reactive: Cu, Ag, Au.

4. Reactivity Series

Arranged in decreasing order of reactivity.

K > Na > Ca > Mg > Al > Zn > Fe > Pb > (H) > Cu > Hg > Ag > Au.

Metals above H: displace hydrogen from acids.

Metals below H: do not displace hydrogen.

5. Ionic Compounds

Formed by transfer of electrons from metal to non-metal.

Example:

Na + Cl → Na⁺ + Cl⁻ → NaCl.

Mg + Cl₂ → Mg²⁺ + 2Cl⁻ → MgCl₂.

Properties:

1. Solid, hard, brittle.
2. High melting and boiling points.
3. Soluble in water, insoluble in petrol/kerosene.
4. Conduct electricity in molten state or in aqueous solution, not in solid state.

6. Occurrence of Metals

Minerals – naturally occurring substances with metals.

Ores – minerals from which metals can be extracted profitably.

Gangue – impurities (sand, soil, etc.).

Extraction of Metals

• Depends on position in reactivity series.
• Low reactivity metals (Cu, Ag, Au)
• Found in free state.
• Obtained by heating ores in air.
• Medium reactivity metals (Zn, Fe, Pb, etc.)

Present as oxides, sulphides, carbonates.

• Sulphides → roasted to oxides.
• Carbonates → calcined to oxides.

Oxides reduced with carbon or by displacement.

High reactivity metals (Na, K, Al, Ca, Mg)

Obtained by electrolytic reduction of molten salts.

Refining of Metals

Impure metal (anode), pure metal (cathode), electrolyte (metal salt solution).

On electrolysis: pure metal deposited on cathode, impurities → anode mud.

7. Corrosion

• Silver: turns black (Ag₂S).
• Copper: green coating (basic copper carbonate).
• Iron: rusts (hydrated iron oxide).

Conditions for rusting: presence of both air (oxygen) and moisture.

Prevention of Corrosion

Painting, oiling, greasing, galvanising (zinc coating), chrome plating, anodising, alloying.

Stainless steel (Fe + Cr + Ni) does not rust.

8. Alloys

Homogeneous mixture of metals (or metal + non-metal).

Properties: harder, stronger, resistant to corrosion, lower conductivity, lower melting points.

Examples:

• Brass: Cu + Zn.
• Bronze: Cu + Sn.
• Solder: Pb + Sn (low melting, used in welding wires).
• Amalgam: alloy with mercury.

24-carat gold: pure (soft). 22-carat gold: mixed with Cu/Ag for hardness.

Stainless steel: Fe + Cr + Ni.