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Chapter 3: Metals and Non-Metals

VIGYAN

Chapter 3: Metals and Non-Metals

Class X Science - Student Support Material

Physical Properties of Metals and Non-Metals

Property Metals Non-Metals
State of Existence Solids at room temperature (Exception: Mercury is liquid). Exist in all three states (Solid, Liquid, Gas).
Lustre Shiny appearance. Dull appearance (Exception: Iodine crystals have bright lustre).
Hardness Generally hard (Exceptions: Na, K are soft; Hg is liquid). Not very hard (Diamond is the hardest natural substance).
Sonority Sonorous (produce sound when struck). Non-sonorous.
Malleability Malleable (can be beaten into thin sheets). Not malleable; brittle (break into powder).
Ductility Ductile (can be drawn into thin wires). Non-ductile.
Electrical Conductivity Good conductors. Poor conductors (Exception: Graphite).
Melting Point High melting point (Exceptions: Gallium and Caesium melt on palm). Low melting point (Exception: Diamond).

Chemical Properties of Metals and Non-Metals

1. Reaction with Oxygen

Metals: Form basic oxides.
\( \text{Metal} + \text{Oxygen} \rightarrow \text{Metal Oxide} \)

  • Na and K react vigorously: \( 4Na(s) + O_2(g) \rightarrow 2Na_2O(s) \)
  • Amphoteric Oxides: Metal oxides that show both acidic and basic behavior (e.g., Aluminium oxide, Zinc oxide).
    \( Al_2O_3 + 6HCl \rightarrow 2AlCl_3 + 3H_2O \)
    \( Al_2O_3 + 2NaOH \rightarrow 2NaAlO_2 + H_2O \) (Sodium Aluminate)

Non-Metals: Form acidic or neutral oxides.
\( C + O_2 \rightarrow CO_2 \) (Acidic)
\( S + O_2 \rightarrow SO_2 \) (Acidic, dissolves in water to form Sulphurous acid)

2. Reaction with Water

Metals: \( \text{Metal} + \text{Water} \rightarrow \text{Metal Oxide/Hydroxide} + H_2 \)

  • Cold Water: Na, K, Ca react violently. \( 2Na + 2H_2O \rightarrow 2NaOH + H_2 + \text{Heat} \)
  • Hot Water: Mg reacts to form \( Mg(OH)_2 \).
  • Steam: Al, Fe, Zn react with steam. \( 3Fe(s) + 4H_2O(g) \rightarrow Fe_3O_4(s) + 4H_2(g) \)
  • No Reaction: Pb, Cu, Ag, Au do not react with water.

Non-Metals: Do not react with water or steam.

3. Reaction with Dilute Acids

Metals: \( \text{Metal} + \text{Dilute Acid} \rightarrow \text{Salt} + H_2 \)

  • \( 2Na + H_2SO_4 \rightarrow Na_2SO_4 + H_2 \)
  • Note: Hydrogen gas is not evolved with Nitric Acid (\( HNO_3 \)) because it is a strong oxidizing agent (oxidizes \( H_2 \) to water). Exceptions: Mg and Mn react with very dilute \( HNO_3 \) to evolve \( H_2 \).

Non-Metals: Do not react with dilute acids.

4. Reaction with Salt Solutions (Displacement)

A more reactive metal/non-metal displaces a less reactive one from its salt solution.

  • Metal: \( Zn(s) + CuSO_4(aq) \rightarrow ZnSO_4(aq) + Cu(s) \)
  • Non-Metal: \( 2NaBr(aq) + Cl_2(g) \rightarrow 2NaCl(aq) + Br_2(aq) \)

5. Reaction with Chlorine

  • Metals: Form ionic chlorides. \( 2Na + Cl_2 \rightarrow 2NaCl \)
  • Non-Metals: Form covalent chlorides. \( H_2 + Cl_2 \rightarrow 2HCl \)

Ionic Compounds

Compounds formed by the transfer of electrons from a metal to a non-metal are known as Ionic Compounds or Electrovalent Compounds.

Formation of Sodium Chloride (NaCl):

  • Sodium (Na) loses 1 electron: \( Na \rightarrow Na^+ + e^- \) (2,8,1 to 2,8)
  • Chlorine (Cl) gains 1 electron: \( Cl + e^- \rightarrow Cl^- \) (2,8,7 to 2,8,8)
  • Result: \( [Na]^+ [Cl]^- \)

Properties of Ionic Compounds

  • Physical Nature: Solid and hard due to strong force of attraction between ions.
  • Melting/Boiling Points: High, as considerable energy is required to break the strong inter-ionic attraction.
  • Solubility: Soluble in water; insoluble in organic solvents (kerosene, petrol).
  • Conduction of Electricity: Conduct electricity in molten state or aqueous solution (due to movement of ions). Do not conduct in solid state.

Occurrence and Extraction of Metals

  • Minerals: Naturally occurring substances with uniform composition.
  • Ores: Minerals from which metal can be profitably extracted.

Steps in Extraction

  1. Concentration of Ore: Removal of gangue (impurities).
  2. Conversion to Metal Oxide:
    • Roasting: Heating sulphide ores in excess air.
      \( 2ZnS + 3O_2 \xrightarrow{\text{Heat}} 2ZnO + 2SO_2 \)
    • Calcination: Heating carbonate ores in limited air.
      \( ZnCO_3 \xrightarrow{\text{Heat}} ZnO + CO_2 \)
  3. Reduction to Metal:
    • Using Carbon (Coke): \( ZnO + C \rightarrow Zn + CO \)
    • Thermite Reaction: Reduction using Aluminium (highly exothermic, used for welding railway tracks).
      \( Fe_2O_3(s) + 2Al(s) \rightarrow 2Fe(l) + Al_2O_3(s) + \text{Heat} \)
  4. Electrolytic Reduction (For highly reactive metals Na, Mg, Al):
    Metals are obtained at the cathode.
    At Cathode: \( Na^+ + e^- \rightarrow Na \)
    At Anode: \( 2Cl^- \rightarrow Cl_2 + 2e^- \)
  5. Refining: Electrolytic refining is used for Cu, Zn, Sn, Ag, Au. Impure metal is anode, pure metal is cathode.

[DIAGRAM: Electrolytic Refining of Copper showing Anode (Impure), Cathode (Pure), and Anode Mud]

Corrosion

The eating away of metal surfaces by the action of air, moisture, or chemicals.

  • Silver: Turns black due to Silver Sulphide (\( Ag_2S \)).
  • Copper: Turns green due to Basic Copper Carbonate (\( CuCO_3 \cdot Cu(OH)_2 \)).
  • Iron: Rusts (brown flaky substance) due to Hydrated Iron Oxide (\( Fe_2O_3 \cdot xH_2O \)).

Prevention of Rusting

  • Painting, Greasing, Oiling.
  • Galvanization: Coating iron with a thin layer of Zinc.
  • Alloying: Homogeneous mixture of two or more metals/non-metals.
    • Brass: Copper + Zinc
    • Bronze: Copper + Tin
    • Solder: Lead + Tin (Low melting point, used for welding electrical wires)
    • Amalgam: Alloy containing Mercury.
    • Stainless Steel: Iron + Nickel + Chromium (Does not rust).

Question Bank

Multiple Choice Questions

  1. An aluminium strip is kept immersed in freshly prepared ferrous sulphate solution. The change observed is:
    Ans: (a) Green solution slowly gets decolourised with brown deposits.
  2. Galvanisation is a method of protecting iron from rusting by coating with a thin layer of:
    Ans: (c) Zinc
  3. Which pair of metals exists in their native state in nature?
    Ans: (a) Ag and Au
  4. The process in which a carbonate ore is heated strongly in the absence of air to convert it into metal oxide is called:
    Ans: (c) Calcination
  5. Rusting of iron takes place in:
    Ans: (a) Ordinary water

Assertion-Reason Questions

(a) Both A & R true, R is correct explanation. (c) A true, R false. (d) A false, R true.

  1. Assertion: Gas bubbles are observed when sodium carbonate is added to dilute HCl.
    Reason: Carbon dioxide is given off in the reaction.
    Ans: (a)
  2. Assertion: \( MgCl_2 \) is a covalent compound.
    Reason: \( MgCl_2 \) is a good conductor of electricity in molten state.
    Ans: (d) Assertion is false (It is ionic), Reason is true.

Short Answer Questions

Q1. An element A burns with golden flame in air. It reacts with element B (atomic number 17) to give product C. Aqueous solution of C on electrolysis gives compound D and liberates hydrogen. Identify A, B, C, D.
Ans:
A = Sodium (Na)
B = Chlorine (Cl)
C = Sodium Chloride (NaCl)
D = Sodium Hydroxide (NaOH)
Reaction: \( 2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g) \)

Q3. Write electron dot structures for sodium, oxygen and magnesium. Show formation of \( Na_2O \) and \( MgO \).
Ans:
Na (2,8,1) loses 1e. O (2,6) gains 2e. Two Na atoms transfer 1e each to one O atom.
Mg (2,8,2) loses 2e. O (2,6) gains 2e. One Mg atom transfers 2e to one O atom.

Q5. A solution of \( CuSO_4 \) was kept in an iron pot. After few days the iron pot had holes. Explain.
Ans: Iron is more reactive than copper. It displaces copper from copper sulphate solution.
\( Fe(s) + CuSO_4(aq) \rightarrow FeSO_4(aq) + Cu(s) \).
The iron pot gets consumed in the reaction, causing holes.

Long Answer Questions

Q1. (a) Write the chemical name of the coating on silver and copper articles when exposed to air. (b) Explain galvanisation. (c) Define alloy and give examples.
Ans:
(a) Silver: Silver Sulphide (\( Ag_2S \)). Copper: Basic Copper Carbonate (\( CuCO_3 \cdot Cu(OH)_2 \)).
(b) Galvanisation: Coating iron/steel with a thin layer of Zinc to prevent rusting.
(c) Alloy: Homogeneous mixture of two or more metals (or metal and non-metal). e.g., Brass (Cu+Zn), Stainless Steel (Fe+Ni+Cr).

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