s-Block Elements JEE Notes, Download PDF & Formulas

s-Block Elements JEE Notes: Important Concepts

The s-block consists of Group 1 (alkali metals) and Group 2 (alkaline earth metals). Their distinguishing feature is the valence electronic configuration of $$ns^{1}$$ and $$ns^{2}$$ respectively, where $$n$$ is the period number. All of them are highly reactive metals that occur in nature only as compounds.

• Alkali metals (Group 1): Li, Na, K, Rb, Cs, Fr
• Alkaline earth metals (Group 2): Be, Mg, Ca, Sr, Ba, Ra
• Common oxidation states: +1 for Group 1, +2 for Group 2.
• Low ionisation enthalpy: Decreases down the group, making the elements more reactive.
• Flame colouration: Except Be and Mg, all s-block metals impart characteristic colours to a non-luminous Bunsen flame due to $$ns\rightarrow np$$ electronic transition.
• Diagonal relationship: Li with Mg, Be with Al show similar size-based properties such as formation of nitrides.
• Hydration enthalpy trend: Falls down the group. Smaller ions (Li⁺, Be²⁺) are most strongly hydrated, explaining their exceptional solubility patterns.

Periodic Trends and General Characteristics of Group 1 and Group 2

Atomic and Ionic Radii

Both groups show a steady increase in radius down the group because an extra electron shell is added each period. Group 2 ions are smaller than Group 1 ions of the same period because of higher nuclear charge.

Ionisation Enthalpy (IE)

Group 1 shows the lowest IE₁ in every period, which is why these metals are never found free in nature. A sharp hike between IE₁ and IE₂ for Group 1 explains why they almost exclusively form +1 ions.

Electronegativity, Density and Melting Point

• Electronegativity is lowest at the extreme left of the periodic table and decreases further down a group.
• Density rises down each group because mass increases faster than atomic volume at first; however K is lighter than Na due to crystal packing.
• Melting points drop sharply from Li → Cs and from Be → Ba because metallic bonding weakens as radius increases.

Flame Colour Tests

Be²⁺ and Mg²⁺ do not impart colour because their small size and high ionisation enthalpy require more energy than provided by the flame.

After mastering these periodic trends, practise mixed assertion-reason questions inside the JEE Questions to see how the examiner cross-connects data across the two groups.

Important Compounds and Reactions of Alkali & Alkaline Earth Metals

Reactivity with Water and Oxygen

• $$2\,Li + H_{2}O \;\longrightarrow\; 2\,LiOH + H_{2}$$ (moderate, no flame)
• $$2\,Na + 2\,H_{2}O \;\longrightarrow\; 2\,NaOH + H_{2}\uparrow$$ (vigorous, yellow flame)
• $$2\,K + 2\,H_{2}O \;\longrightarrow\; 2\,KOH + H_{2}\uparrow + \text{violet flame}$$
• $$2\,Mg + O_{2} \; \overset{\Delta}{\longrightarrow} \; 2\,MgO$$ (burns with dazzling white light)

Ammoniacal Solubility of Alkali Metals

Alkali metals dissolve in liquid ammonia to give deep blue, conducting solutions due to solvated electrons.

$$M + x\,NH_{3} \;\rightleftharpoons\; [M(NH_{3})_{x}]^{+} + e^{-}_{(solvated)}$$

Industrial Preparation Processes

• Solvay (Ammonia-Soda) Process: Na₂CO₃ is obtained from NaCl, NH₃ and CO₂ via precipitation of NaHCO₃.
• Nelson Cell: Down-stream electrolysis of fused NaCl produces metallic Na and Cl₂ gas.
• Dow’s Process: Mg is extracted from seawater by precipitating Mg(OH)₂ with Ca(OH)₂ followed by electrolysis of MgCl₂.
• Serpeck Process: Purifies bauxite of silica impurities using NaAlO₂ formation at high temperatures.

Hardness and Softness of Water

Biological and Commercial Uses

• Mg²⁺ is the central ion in chlorophyll. Ca²⁺ builds bones and triggers blood clotting.
• CaO (quicklime) is used in basic slag formation in the steel industry.
• BaSO₄ opaque suspensions act as radio-contrast agents in gastrointestinal X-rays.

Once you finish the compound-wise notes, flip through the printable JEE Formula Sheets so you do not miss an industrial process temperature or catalyst in the exam hall.

Worked Example 1: Solubility Order

Question: Arrange $$MgF_{2},\; CaF_{2},\; SrF_{2},\; BaF_{2}$$ in increasing order of solubility in water.
Solution: Lattice energy decreases down the group faster than hydration enthalpy. Therefore solubility increases down the group.

Order: $$MgF_{2} \lt CaF_{2} \lt SrF_{2} \lt BaF_{2}$$

Worked Example 2: Calculating Degree of Hardness

Question: A 100 mL water sample requires 12.5 mL of 0.01 M EDTA to reach the end-point. Compute total hardness as CaCO₃ equivalents (ppm).
Solution:

1. Moles of EDTA = 0.01 × 0.0125 = 1.25 × 10^-4
2. 1 mol EDTA complexes 1 mol CaCO₃ equivalent ⇒ millimoles CaCO₃ = 0.125
3. Mass of CaCO₃ = 0.125 × 100 = 12.5 mg
4. Sample volume = 100 mL = 0.1 L = 0.1 kg

Hardness = $$\dfrac{12.5\,\text{mg}}{0.1\,\text{kg}}$$ = 125 ppm

Biological, Industrial and Analytical Uses

Biological Importance

• Mg²⁺ activates about 300 enzymes including ATPases.
• Ca²⁺ concentration in human blood is tightly regulated at 9–11 mg 100 mL^-1.
• Li⁺ salts have psychiatric applications in treating bipolar disorder (not in JEE syllabus but often asked as a fact).

Industrial Materials

• Portland cement: Roasting limestone and clay gives Clinker (CaO·SiO₂·Al₂O₃) which is ground with gypsum.
• Plaster of Paris: $$2\,CaSO_{4}\cdot2H_{2}O \;\xrightarrow{120^{\circ}C}\; (CaSO_{4})_{2}\cdot H_{2}O + 3\,H_{2}O$$ – sets by rehydration.
• Soda lime: Mixture of CaO and NaOH, used in rebreathing apparatus to carbon-trap CO₂.

Analytical Chemistry Uses

To see how these facts show up in integer-type questions, attempt s-block sections from the last five papers inside JEE Mains Previous Papers just after finishing this note.

Important Formulas and Results at a Glance

$$E^{\circ}(Li^{+}/Li) = -3.04\;V$$ gives Li the strongest reducing power in aqueous solution among all metals.

$$CaCO_{3} \;\xrightarrow{\Delta}\; CaO + CO_{2}\uparrow$$ is the basis of lime manufacture and the thermal test for carbonate radicals.

Keep this table pinned next to your desk. It covers every quantitative relation that appeared from 2013 to 2023 in both papers.

JEE Important Points, Common Mistakes and Quick Revision

• Never write LiCl·2H₂O as a typical halide hydrate. Only Li halides are hydrated owing to high hydration energy.
• Do not confuse flame colours. Na always masks others; use cobalt-blue glass to filter Na lines in the lab.
• Oxide nature: $$BeO$$ : amphoteric, $$MgO, CaO$$ : basic. Many students mark MgO amphoteric – incorrect.
• Solubility reversal: All carbonates become less soluble down the group, but hydroxides of Group 2 become more soluble from Mg to Ba.
• Diagonal relationship exceptions: Li forms polymeric $$Li[NH_{2}]$$ unlike Mg. Do not over-generalise.

1. 15-minute drill: Recite the flame colours chart.
2. 10-minute drill: Balance the Solvay and plaster of Paris equations from memory.
3. 5-minute drill: Redraw the hydration energy vs atomic number graph – this cements periodic trend logic.

If you still mix up lattice and hydration energies, revisit two solved numericals from the earlier section, then jump into topic-wise quizzes available under our JEE Mains Online Coaching dashboards.