Periodic table arranges elements by atomic number, electronic configuration. Long form: 7 periods (rows), 18 groups (columns). Sub group A (representative), sub group B (transition). Four blocks: s (IA,IIA, ns¹ or ns²), p (IIIA–VIIIA, ns²np¹⁻⁶), d (subgroup B, ns² (n-1)d¹⁻¹⁰), f (lanthanides/actinides, below main, ns²(n-2)f¹⁻¹⁴). Position from configuration: sulphur (16) 1s²2s²2p⁶3s²3p⁴ → period 3, VIA.
IA & IIA: increase Li→Fr, Be→Ra. Li 152 pm, Fr 348 pm; Be 112, Ra 215 (table 1.1).
| IA (pm) | IIA (pm) |
|---|---|
| Li 152, Na 186, K 227, Rb 248, Cs 265, Fr 348 | Be 112, Mg 145, Ca 194, Sr 219, Ba 253, Ra 215 |
IIIA: B→Tl increase, but Ga slightly smaller than Al due to d-contraction.
IIIA: Ga higher IE than Al (3d e⁻ poor shield). IVA: Sn & Pb similar due to lanthanide contraction. VA–VIIIA decrease down group.
| Group | IA | IIIA | VA | VIIA |
|---|---|---|---|---|
| Period2 | Li 520 | B 800 | N 1400 | F 1680 |
| Period3 | Na 490 | Al 577 | P 1060 | Cl 1250 |
| decrease down group (kJ/mol) | ||||
IA & IIA: high electrical conductivity. IIIA moderate, IVA variable (C poor, Si moderate), VA–VIIA poor, noble gases extremely low. (table 1.5)
Oxidation states (table 1.6): IA +1, IIA +2, IIIA +3, IVA -4,-2,+2,+4, VA -3,-2,+3,+5, VIA -2,+2,+4,+6, VIIA -1,+1,+3,+5,+7, noble gases 0.
Alkali metals low mp (weak metallic), alkaline earth higher. C (diamond) high, N₂ low, halogens low. Beryllium unique: harder, high mp, covalent, protective oxide. (media/image3.png)
s-block reactions: with O₂: Li → Li₂O (normal), Na → Na₂O₂ (peroxide), K,Rb,Cs → superoxide MO₂. Alkaline earth: Be,Mg,Ca → normal oxide MO; Sr,Ba → peroxide MO₂.
With water: alkali → MOH + H₂ (violent). Be no reaction, Mg with steam. With halogens: 2M + X₂ → 2MX (IA); M + X₂ → MX₂ (IIA). With nitrogen: 6Li + N₂ → 2Li₃N ; 3Mg + N₂ → Mg₃N₂. With hydrogen: 2M + H₂ → 2MH (hydrides). With alcohol: 2M + 2C₂H₅OH → 2C₂H₅OM + H₂.
Electrolysis of brine (NaCl aq) using mercury cathode. At titanium anode: 2Cl⁻ → Cl₂ + 2e⁻ (also OH⁻ oxidized). Na⁺ forms Na/Hg amalgam, then in denuder: 2Na/Hg + 2H₂O → 2NaOH + H₂ + Hg. Mercury recycled. NaOH properties: solid, mp 318°C, soluble, corrosive. Reacts with acids (NaOH + HCl → NaCl + H₂O), with FeCl₃ → Fe(OH)₃ brown ppt, with Al/Zn: 2NaOH + 2Al + 2H₂O → 2NaAlO₂ + 3H₂ ; with chlorine hot: 6NaOH + 3Cl₂ → NaClO₃ + 5NaCl + 3H₂O. Uses: detergents, bleach, drain cleaner.
With oxygen: 2N₂ + O₂ (catalyst) → 2N₂O; 4P + 3O₂(limited) → 2P₂O₃; excess → P₂O₅; S + O₂ → SO₂; 2F₂ + O₂ → 2F₂O.
With water: 2Al + 6H₂O → 2Al(OH)₃ + 3H₂ (slow due to oxide); Si + 2H₂O (steam) → SiO₂ + 2H₂; 2P₄ + 12H₂O → 3H₃PO₄ + 5PH₃; Cl₂ + H₂O → HCl + HOCl.
With halogens: 2Al+3Cl₂→2AlCl₃; C+2Cl₂→CCl₄; N₂+3Cl₂→2NCl₃; O₂+2F₂→2OF₂.
With nitrogen: 2B+N₂→2BN; 3C+2N₂→C₃N₄; 6P+5N₂→2P₃N₅; 3Cl₂+N₂→2NCl₃.
With hydrogen: Si+2H₂→SiH₄; N₂+3H₂⇌2NH₃; S+H₂→H₂S; Cl₂+H₂→2HCl.
Bond enthalpy F₂ low (weak bond) → high reactivity. Oxidizing power: F₂ > Cl₂ > Br₂ > I₂. Reducing power of halides: I⁻ > Br⁻ > Cl⁻ > F⁻. Chlorine displaces Br⁻, I⁻ from salts: 2NaBr + Cl₂ → 2NaCl + Br₂; 2NaI + Br₂ → 2NaBr + I₂. Chlorine as auto redox.
Step1: S + O₂ → SO₂ (burner, impurities removed to avoid catalyst poisoning).
Step2: 2SO₂ + O₂ ⇌ 2SO₃ (V₂O₅, 400-500°C, 1-2 atm, exothermic -45 kcal/mol).
Step3: SO₃ + H₂SO₄ → H₂S₂O₇ (oleum), then diluted.
Properties: oxidizing agent (C + 2H₂SO₄ → CO₂ + 2SO₂ + 2H₂O; Cu + 2H₂SO₄ → CuSO₄ + SO₂ + 2H₂O); dehydrating (sugar → C); sulphonating (benzene → benzenesulphonic acid); dibasic acid.
1. flow diagram contact process. 2. Castner Kellner cell diagram. 3. balanced equations: Al + conc. H₂SO₄, FeCl₃ + NaOH, Na + excess air, Mg + N₂, K + alcohol, Cl₂ + NaOH. 4. bleaching powder prep & reaction. 5. group trend atomic radii, IE, electronegativity alkali metals.
20 mcqs – select option, turns green if correct (others red). submit shows score & key.