Unit 10.2: Alkali and Alkaline Earth Metals (5 Teaching Hours)
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Alkali Metals
- General Characteristics of Alkali Metals
- Group 1 elements (Li, Na, K, Rb, Cs, Fr) with one valence electron (ns¹).
- Soft, low melting points, highly reactive due to low ionization energy; reactivity increases down the group.
- Form basic oxides (e.g., Na₂O) and hydroxides (e.g., NaOH).
- Stored in oil to prevent reaction with air/moisture.
- Figure 1: Periodic Trends in Alkali Metals (Diagram showing trends in ionization energy and reactivity).
- Sodium
- Extraction from Down’s Process
- Electrolysis of molten NaCl with CaCl₂ (lowers melting point) in Down’s cell; Na forms at cathode, Cl₂ at anode.
- Figure 2: Down’s Process (Diagram showing Down’s cell setup).
- Properties
- Action with Oxygen: Forms sodium peroxide: 2Na + O₂ → Na₂O₂.
- Action with Water: Forms NaOH and H₂: 2Na + 2H₂O → 2NaOH + H₂.
- Action with Acids: Reacts to form salts and H₂: 2Na + 2HCl → 2NaCl + H₂.
- Action with Non-Metals: Forms compounds like NaCl, Na₂S (e.g., 2Na + Cl₂ → 2NaCl).
- Action with Ammonia: Forms sodamide: 2Na + 2NH₃ → 2NaNH₂ + H₂.
- Uses
- Coolant in nuclear reactors.
- Synthesis of chemicals (e.g., NaOH, Na₂CO₃).
- Sodium vapor lamps.
- Extraction from Down’s Process
- Properties and Uses of Sodium Hydroxide (NaOH)
- Precipitation Reaction: Forms insoluble hydroxides with metal ions (e.g., FeCl₃ + 3NaOH → Fe(OH)₃↓ + 3NaCl).
- Action with Carbon Monoxide: Forms sodium formate at high pressure: NaOH + CO → HCOONa.
- Uses: Soap and detergent production, paper industry, petroleum refining, pH regulation.
- Figure 3: Precipitation Reaction of NaOH (Diagram showing Fe(OH)₃ precipitation).
- Properties and Uses of Sodium Carbonate (Na₂CO₃)
- Action with CO₂: Forms sodium bicarbonate: Na₂CO₃ + CO₂ + H₂O → 2NaHCO₃.
- Action with SO₂: Forms sodium sulphite: Na₂CO₃ + SO₂ → Na₂SO₃ + CO₂.
- Action with Water: Hydrolyses to form alkaline solution: Na₂CO₃ + H₂O ⇌ NaHCO₃ + NaOH.
- Precipitation Reactions: Forms insoluble carbonates (e.g., CaCl₂ + Na₂CO₃ → CaCO₃↓ + 2NaCl).
- Uses: Glass manufacturing, water softening, detergent production, pH buffer.
- General Characteristics of Alkali Metals
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Alkaline Earth Metals
- General Characteristics of Alkaline Earth Metals
- Group 2 elements (Be, Mg, Ca, Sr, Ba, Ra) with two valence electrons (ns²).
- Less reactive than alkali metals; reactivity increases down the group.
- Form basic oxides (e.g., CaO) and hydroxides (e.g., Ca(OH)₂).
- Figure 4: Periodic Trends in Alkaline Earth Metals (Diagram showing trends in ionization energy and reactivity).
- Molecular Formula and Uses of Compounds
- Quick Lime (CaO): Used in cement, mortar, and neutralizing acidic soils.
- Bleaching Powder (Ca(OCl)Cl): Used as disinfectant, bleaching agent in textiles/paper.
- Magnesia (MgO): Used as refractory material, antacid in medicine.
- Plaster of Paris (CaSO₄·½H₂O): Used in construction, medical casts, sculptures.
- Epsom Salt (MgSO₄·7H₂O): Used as laxative, fertilizer, bath salts.
- Solubility of Hydroxides, Carbonates, and Sulphates
- Hydroxides: Solubility increases down the group (Be(OH)₂ insoluble, Ba(OH)₂ more soluble) due to decreasing lattice energy.
- Carbonates: Solubility decreases down the group (MgCO₃ soluble, BaCO₃ insoluble) due to increasing lattice stability.
- Sulphates: Solubility decreases down the group (MgSO₄ soluble, BaSO₄ insoluble) due to increasing lattice energy.
- Figure 5: Solubility Trends of Alkaline Earth Compounds (Diagram showing solubility trends).
- Stability of Carbonates and Nitrates
- Carbonates: Thermal stability increases down the group (BeCO₃ least stable, BaCO₃ most stable) due to increasing ionic radius stabilizing lattice.
- Nitrates: Thermal stability increases down the group (Be(NO₃)₂ decomposes easily, Ba(NO₃)₂ more stable) due to larger cations stabilizing anion.
- General Characteristics of Alkaline Earth Metals