s and p-Block Elements

Alkali Metals (Group 1)

Group 1 elements: Li, Na, K, Rb, Cs, Fr. Fr is radioactive (longest isotope Fr-223, half-life 21 min). Hydroxides form strong bases (alkalies).

Electronic Configuration & Discovery

Occurrence & Ores

Extraction

Alkali metals are strong reducing agents, extracted by electrolysis of fused chlorides (e.g., Downs cell for Na from fused NaCl + CaCl₂).

Physical Properties

Trends: Atomic/ionic radii ↑, density ↑ (K < Na due to larger size), m.p./b.p. ↓, IE ↓, electronegativity ↓, electropositive character ↑ down the group.

Chemical Properties

Hydrides, Oxides, Hydroxides

Hydrides (MH): Ionic, stability ↓ from LiH to CsH.
Oxides: Li₂O, Na₂O₂, KO₂ etc.
Hydroxides (MOH): Strong bases, solubility ↑ down group.

Carbonates & Bicarbonates

Li₂CO₃ decomposes on heating; others stable. Solubility ↑ down group.

Anomalous Behaviour of Lithium

• Small size, high charge density → covalent compounds.
• Li₂CO₃, LiOH, LiF less soluble.
• Forms Li₃N, Li₂O (not peroxide).
• Hardest among alkali metals.

Diagonal Relationship: Li & Mg

Similar EN, hardness, decompose carbonates/nitrates, form monoxides, etc.

Compounds of Na & K

NaCl, NaOH (caustic soda), Na₂CO₃ (soda ash), NaHCO₃ (baking soda), Na₂SO₄, microcosmic salt (NaNH₄HPO₄·4H₂O).

Alkaline Earth Metals (Group 2)

Occurrence & Ores

Extraction

Be, Mg by reducing oxides with C. Others by electrolysis of fused salts.

Physical Properties

Trends: Radii ↑, density irregular (↓ to Ca, then ↑), m.p./b.p. irregular, IE ↓, electropositive ↑ down group.

Chemical Properties

Anomalous Behaviour of Beryllium

• Small size, high IE → covalent compounds.
• BeO amphoteric; Be(OH)₂ amphoteric.
• No reaction with water/acids.
• Forms Be₂C (methanide).

Diagonal Relationship: Be & Al

Similar properties: amphoteric oxides, form complexes, chlorides polymeric.

Compounds of Mg & Ca

MgO (magnesia cement), Mg(OH)₂ (milk of magnesia), MgSO₄ (Epsom salt), CaO (quicklime), Ca(OH)₂ (slaked lime), CaOCl₂ (bleaching powder), CaSO₄·½H₂O (plaster of Paris), Ca₃(PO₄)₂ (phosphorite).

Cement: Mixture of CaO (50-60%), SiO₂ (20-25%), Al₂O₃ (5-10%), etc.

Boron Family (Group 13)

Occurrence & Ores

B: Borax (Na₂B₄O₇·10H₂O), Colemanite (Ca₂B₆O₁₁·5H₂O).

Al: Bauxite (Al₂O₃·2H₂O), Cryolite (Na₃AlF₆).

Extraction

B by reducing B₂O₃ with Mg/Na. Al by Hall-Heroult process (electrolysis of Al₂O₃ in cryolite).

Physical Properties

Atomic radii ↑, IE ↓ (Ga > Al due to d-block contraction), EN ↓, density ↑.

Chemical Properties

Hydrides: Boranes (B₂H₆ electron deficient). Oxides: B₂O₃ acidic, Al₂O₃ amphoteric, others basic.

Anomalous Behaviour of Boron

• Non-metal, covalent compounds, acidic oxide.
• Forms BF₃ (Lewis acid), no dimer like AlCl₃.

Diagonal Relationship: B & Si

Both non-metals, form covalent compounds, acidic oxides, hydrides hydrolysed, form esters with alcohols.

Compounds of Boron & Al

Boranes (B₂H₆), Borax (bead test), Boric acid (H₃BO₃), Al₂O₃ (corundum), AlCl₃ (dimer), Thermite (Al + Fe₂O₃).

Carbon Family (Group 14)

Occurrence & Ores

C: Coal, petroleum, natural gas, carbonates.

Si: Silica (SiO₂), silicates.

Sn: Cassiterite (SnO₂).

Pb: Galena (PbS).

Extraction

C not extracted. Si by reducing SiO₂ with C. Sn/Pb from ores by roasting and reduction.

Physical Properties

Allotropy: C (diamond, graphite), Si, Ge, Sn (white, gray), Pb no.

Trends: Radii ↑, density ↑, m.p./b.p. ↓ then ↑, IE ↓, EN ↓, catenation C >> Si > Ge ≈ Sn > Pb.

Chemical Properties

Hydrides: CH₄ stable, silanes less, catenation in C hydrides.

Oxides: CO neutral, CO₂ acidic, SiO₂ acidic, others amphoteric/basic.

Halides: CCl₄, SiCl₄ hydrolysed, stability ↓ down group.

Anomalous Behaviour of Carbon

• High m.p./b.p., catenation, pπ-pπ bonds.
• CO gas, others solids; C neutral hydride, others acidic.

Diagonal Relationship: C & Si

Both non-metals, form covalent compounds, acidic oxides, hydrides hydrolysed.

Compounds of C & Si

CO, CO₂, CS₂, SiO₂ (silica gel, silicates), Silicones (polymers), Glass (varieties).

Tin: SnO, SnO₂, SnCl₂, SnCl₄.

Lead: PbO (litharge), Pb3O4 (red lead), PbCl2, PbCl4.

Nitrogen Family (Group 15)

Occurrence & Ores

N: Air (78%), nitrates. P: Phosphorite (Ca3(PO4)2), bones.

Extraction

N from air fractionation. P from bones or phosphorite.

Physical Properties

Allotropy: N (diatomic), P (white, red, black), As, Sb, Bi solids.

Trends: Radii ↑, IE ↓, EN ↓, metallic character ↑.

Chemical Properties

Hydrides: NH3, PH3, etc., basicity ↓, stability ↓ down group.

Halides: NX3, NX5; stability ↓ down group.

Oxides: N2O, NO, N2O3, NO2, N2O5; acidic character ↑ with O content.

Anomalous Behaviour of Nitrogen

• Gas, diatomic, no pentahalides, pπ-pπ bonds.
• NH3 basic with H-bonding, others not.

Diagonal Relationship: N & Si

Both form hydrides, oxides acidic, halides hydrolysed.

Compounds of N & P

NH3 (Haber process), oxides of N, HNO3 (Ostwald), P allotropes, phosphine (PH3), PCl3, PCl5, oxyacids (H3PO3, H3PO4, etc.).

Oxygen Family (Group 16)

Occurrence & Ores

O: Air (21%), water. S: Gypsum (CaSO4·2H2O), Epsom (MgSO4·7H2O).

Extraction

O from air or water electrolysis. S from Frasch process.

Physical Properties

Allotropy: O (O2, O3), S (rhombic, monoclinic, plastic), Se, Te.

Trends: Radii ↑, IE ↓, EN ↓, metallic ↑, m.p./b.p. ↑.

Chemical Properties

Hydrides: H2O, H2S, etc., acidity ↑, stability ↓ down group.

Oxides: SO2 acidic, SO3 acidic.

Oxyacids: H2SO3, H2SO4, etc.

Anomalous Behaviour of Oxygen

• Gas, diatomic, max covalency 2, H-bonding in H2O.

Diagonal Relationship: O & S

Both form hydrides, oxides, catenation in S.

Compounds of O & S

O3 (ozone), H2S, SO2, SO3, H2SO4 (contact process), Na2S2O3 (hypo).

Halogen Family (Group 17)

Occurrence & Ores

F: Fluorspar (CaF2), Cryolite (Na3AlF6).

Cl: NaCl, Carnallite.

Br: Sea water, KBr.

I: Sea weeds, NaIO3 in Chile saltpetre.

Extraction

F by electrolysis of KHF2 in HF. Cl from brine. Br, I from sea water/mother liquor.

Physical Properties

Coloured gases/liquids/solids. Radii ↑, IE ↓, EN ↓, EA Cl > F > Br > I, O.S. -1 (F only), others +1 to +7.

Chemical Properties

Hydrides: HF > HCl > HBr > HI (acidity ↑, stability ↓).

Oxides: Unstable, acidic.

Oxyacids: HOCl, HClO2, HClO3, HClO4 (strength ↑ with O).

Interhalogens: AB, AB3, AB5, AB7.

Polyhalides: I3⁻, etc.

Anomalous Behaviour of Fluorine

• Low bond energy, high EN, no d-orbitals → only -1 O.S., HF H-bonding.
• Strongest oxidant, etches glass.

Diagonal Relationship: F & O

Both small, high EN, form H-bonding, gaseous hydrides.

Compounds of Halogens

HF, HCl, HBr, HI, Bleaching powder (CaOCl2), I2 (tincture).

Noble Gases (Group 18)

Occurrence

Air: He 5.2×10⁻⁴%, Ne 1.8×10⁻³%, Ar 0.93%, Kr 1.1×10⁻⁴%, Xe 8.7×10⁻⁶%.

Isolation

From air by fractional distillation. He from natural gas, Rn from Ra decay.

Physical Properties

Monoatomic gases, low m.p./b.p. ↑ down group, adsorption ↑ on charcoal.

Chemical Properties

Inert due to stable configuration. Xe forms compounds with F, O: XeF2, XeF4, XeF6, XeO3, XeO4, XeOF4, XeO2F2.

Uses

He: Balloons, diving mix. Ne: Signs. Ar: Welding. Kr/Xe: Lamps. Rn: Therapy.

Important Points & Tips

JEE Main Weightage

Typically 4-6 questions. Focus on properties, trends, compounds, anomalies.