Chapter 2: s-block Elements

s-block Elements: Elements in which s-orbitals are being filled. Includes Group IA (Alkali Metals) and Group IIA (Alkaline Earth Metals).

• Alkali Metals (IA): Li, Na, K, Rb, Cs, Fr. 'Alkali' means ashes. Form strong alkaline solutions. ns¹ configuration. +1 oxidation state.
• Alkaline Earth Metals (IIA): Be, Mg, Ca, Sr, Ba, Ra. Found in earth crust, alkaline nature. ns² configuration. +2 oxidation state.

• Atomic Radius: Increases down the group.
• Ionization Energy: Decreases down the group. Alkali metals have lower I.E than Alkaline earth metals.
• Reactivity: Increases down the group (Cs is most reactive).
• Hydration Energy: Depends on charge density. Li⁺ and Be²⁺ have highest hydration energies. Order: Li⁺ > Na⁺ > K⁺.

Lithium (Li)

• Harder and lighter than other alkali metals.
• Forms normal oxide (Li2O) while others form peroxides/superoxides.
• Reacts with Nitrogen to form Nitride (Li3N).
• Carbonate and Phosphate are insoluble.
• Lithium Nitrate decomposes to Oxide (Li2O), unlike others forming Nitrites.

Beryllium (Be)

• Hard as iron, scratches glass.
• Amphoteric oxide (BeO), others are basic.
• Does not react with water even at red heat.

Sodium (Down's Cell)

Electrolysis of fused NaCl.

• Anode (Graphite): 2Cl⁻ → Cl₂(g) + 2e⁻
• Cathode (Iron): 2Na⁺ + 2e⁻ → 2Na(l)
• Advantages: No metallic fog, liquid sodium collected at 600°C. CaCl2 added to lower MP of NaCl.

Sodium Hydroxide (Nelson's Cell/Diaphragm Cell)

Electrolysis of aqueous NaCl (Brine).

• Anode (Graphite): 2Cl⁻ → Cl₂(g) + 2e⁻
• Cathode (Perforated Steel): 2H₂O + 2e⁻ → H₂(g) + 2OH⁻. Then Na⁺ + OH⁻ → NaOH.
• Diaphragm: Asbestos diaphragm prevents mixing of H₂/Cl₂ and OH⁻/Cl₂.

Gypsum (CaSO4.2H2O)

• Used in cement (2% added to retard setting time).
• Used as fertilizer (source of Ca and S).

Plaster of Paris ((CaSO4)2.H2O)

• Prepared by heating Gypsum at 100°C (loses 3/4 water).
• 2CaSO₄.2H₂O → (CaSO₄)₂.H₂O + 3H₂O.
• Setting: Expands 1% on setting. Used for casts, moulds, bandages.

Lime (CaO)

• Used to neutralize acidic soil.
• Manufacture of bleaching powder, glass, calcium carbide.