s-Block Elements: Reactivity and Compounds (JEE Advanced)

“Alkali and alkaline earth metals-reactivity towards air, water, dihydrogen, halogens, acids; their reducing nature including solutions in liquid ammonia; uses of these elements; general characteristics of their oxides, hydroxides, halides, salts of oxoacids; anomalous behaviour of lithium and beryllium; preparation, properties, and uses of compounds of sodium (sodium carbonate, sodium chloride, sodium hydroxide, sodium hydrogen carbonate) and calcium (calcium oxide, calcium hydroxide, calcium carbonate, calcium sulphate)”

Source: JEE Advanced 2026 Information Bulletin, Annexure-I. Closest JEE Main topic: s, p. d and f block elements, periodic trends in properties of elements.

JEE Main covers general periodic trends, but Advanced specifically tests detailed reactions, anomalous behaviour explanations, and properties of specific compounds like Na₂CO₃ and CaSO₄. You must know exact reactions, conditions, and reasoning behind trends.

• Reactivity increases down the group for alkali metals (lower ionization energy) but alkaline earth metals show some irregularities due to sublimation energy and hydration enthalpy factors
• Lithium is anomalous: forms nitride (Li₃N) directly, carbonate decomposes on heating, hydroxide is weak, and it shows diagonal relationship with magnesium
• Beryllium is anomalous: covalent compounds, amphoteric oxide and hydroxide, no reaction with water, diagonal relationship with aluminium
• Solutions in liquid ammonia: alkali metals dissolve giving blue colour (dilute) due to ammoniated electrons, bronze colour (concentrated) due to metal clusters; these are strong reducing agents
• Solvay process for Na₂CO₃ uses NH₃, CO₂, NaCl, and water; NaHCO₃ precipitates first because it is least soluble
• Plaster of Paris (CaSO₄·½H₂O) sets by absorbing water to form gypsum;ite calcium compounds show different hydration states

• 4Li + O₂ → 2Li₂O (oxide); 2Na + O₂ → Na₂O₂ (peroxide); K + O₂ → KO₂ (superoxide)
• 2Na + 2NH₃ → 2NaNH₂ + H₂ (with Fe catalyst, sodamide formation)
• Na + (x+y)NH₃ → [Na(NH₃)ₓ]⁺ + [e(NH₃)ᵧ]⁻ (blue solution, ammoniated electron)
• CaCO₃ → Caite + CO₂ (above 1070 K); MgCO₃ decomposes at lower temperature than CaCO₃
• 2NaHCO₃ → Na₂CO₃ + H₂O + CO₂ (on heating); Na₂CO₃ does not decompose on heating
• Ca(OH)₂ + Cl₂ → CaOCl₂ + H₂O (bleaching powder formation)
• Thermal stability of carbonates: BeCO₃ < MgCO₃ < CaCO₃ < SrCO₃ < BaCO₃
• Solubility of hydroxides: Be(OH)₂ < Mg(OH)₂ < Ca(OH)₂ < Sr(OH)₂ < Ba(OH)₂

• Confusing products of alkali metals with oxygen: Li gives oxide, Na gives peroxide, K/Rb/Cs give superoxide. Students often write oxide for all.
• Forgetting that Li₂CO₃ and BeCO₃ decompose on heating while Na₂CO₃ and other Group 1 carbonates (except Li) are stable to heat
• Mixing up solubility trends: hydroxides increase in solubility down the group, but sulphates decrease (BaSO₄ is insoluble, used in qualitative analysis)
• Assuming beryllium behaves like other alkaline earth metals: Be forms covalent compounds, its hydroxide is amphoteric, and it does not react with water

Question. When sodium metal is dissolved in liquid ammonia, the resulting solution is blue and paramagnetic. On standing, the blue colour slowly fades and a gas is evolved. Write the reaction for the fading process and explain why the solution becomes diamagnetic. Also, state what happens if iron(III) oxide is added to the fresh blue solution.

Solved twice independently; both solutions agree.