JEE Mains P-Block Notes

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Group 15 Elements (Nitrogen Family) General Electronic Configuration: $ns^2 np^3$ Oxidation States: $-3, +3, +5$. Nitrogen shows $-1, -2, -3, +1, +2, +3, +4, +5$. Bismuth shows only $+3, +5$. Anomalous behaviour of Nitrogen: Small size, high electronegativity, high ionization enthalpy, absence of d-orbitals. Forms $p\pi-p\pi$ multiple bonds. Reactivity towards Hydrogen: Form hydrides $EH_3$. Basic character decreases from $NH_3$ to $BiH_3$. Thermal stability decreases. Reactivity towards Oxygen: Form oxides $E_2O_3, E_2O_4, E_2O_5$. Acidic character decreases down the group. $N_2O_3$ (acidic), $P_2O_3$ (acidic), $As_2O_3$ (amphoteric), $Sb_2O_3$ (amphoteric), $Bi_2O_3$ (basic). Reactivity towards Halogens: Form trihalides ($EX_3$) and pentahalides ($EX_5$). $NX_3$ are stable. $PX_5$ is more covalent than $PX_3$. Reactivity towards Metals: Form binary compounds like $Mg_3N_2, Ca_3P_2$. Nitrogen ($N_2$) Preparation: $NH_4Cl(aq) + NaNO_2(aq) \rightarrow N_2(g) + 2H_2O(l) + NaCl(aq)$ Properties: Colourless, odourless, tasteless, non-toxic gas. Chemically unreactive at ordinary temps due to high bond enthalpy of $N \equiv N$. Uses: In Haber process, food preservation, cryosurgery. Ammonia ($NH_3$) Preparation (Haber's Process): $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ ($\Delta_f H^\circ = -46.1~kJ/mol$). Opt. conditions: high pressure (200 atm), temp (700 K), catalyst ($Fe_2O_3$ with $K_2O, Al_2O_3$). Properties: Planar trigonal pyramidal structure. Basic in nature. Forms coordinate bonds with transition metal ions. Uses: Fertilizers, nitric acid, refrigerants. Oxides of Nitrogen $N_2O$ (Nitrous oxide): Laughing gas, neutral. Prep: $NH_4NO_3 \xrightarrow{\Delta} N_2O + 2H_2O$ $NO$ (Nitric oxide): Neutral. Prep: $2NaNO_2 + 2FeSO_4 + 3H_2SO_4 \rightarrow Fe_2(SO_4)_3 + 2NaHSO_4 + 2H_2O + 2NO$ $N_2O_3$ (Dinitrogen trioxide): Blue solid, acidic. $NO_2$ (Nitrogen dioxide): Reddish brown gas, acidic. Prep: $2Pb(NO_3)_2 \xrightarrow{\Delta} 4NO_2 + 2PbO + O_2$ $N_2O_4$ (Dinitrogen tetroxide): Colourless solid/liquid, acidic. Dimer of $NO_2$. $N_2O_5$ (Dinitrogen pentoxide): Colourless solid, acidic. Nitric Acid ($HNO_3$) Preparation (Ostwald's Process): $4NH_3(g) + 5O_2(g) \xrightarrow{Pt/Rh~gauge,~500K,~9~bar} 4NO(g) + 6H_2O(g)$ $2NO(g) + O_2(g) \rightleftharpoons 2NO_2(g)$ $3NO_2(g) + H_2O(l) \rightarrow 2HNO_3(aq) + NO(g)$ Properties: Strong oxidizing agent. Reacts with metals and non-metals. Conc. $HNO_3$ with Cu: $Cu + 4HNO_3(conc) \rightarrow Cu(NO_3)_2 + 2NO_2 + 2H_2O$ Dilute $HNO_3$ with Cu: $3Cu + 8HNO_3(dilute) \rightarrow 3Cu(NO_3)_2 + 2NO + 4H_2O$ Brown Ring Test: For nitrates. $NO_3^- + 3Fe^{2+} + 4H^+ \rightarrow NO + 3Fe^{3+} + 2H_2O$. Then $[Fe(H_2O)_6]^{2+} + NO \rightarrow [Fe(H_2O)_5(NO)]^{2+} + H_2O$ (brown ring). Phosphorus (P) Allotropic forms: White, Red, Black. White P: $P_4$ tetrahedral, highly reactive, poisonous, soluble in $CS_2$. Red P: Polymeric, less reactive, non-poisonous, insoluble in $CS_2$. Black P: Two forms ($\alpha$ and $\beta$), most stable. Phosphine ($PH_3$): Prep: $Ca_3P_2 + 6H_2O \rightarrow 3Ca(OH)_2 + 2PH_3$. Highly poisonous, weak base. Halides of Phosphorus Phosphorus Trichloride ($PCl_3$): Prep: $P_4 + 6Cl_2 \rightarrow 4PCl_3$. Hydrolyses: $PCl_3 + 3H_2O \rightarrow H_3PO_3 + 3HCl$. Phosphorus Pentachloride ($PCl_5$): Prep: $P_4 + 10Cl_2 \rightarrow 4PCl_5$. Hydrolyses: $PCl_5 + H_2O \rightarrow POCl_3 + 2HCl$; $POCl_3 + 3H_2O \rightarrow H_3PO_4 + 3HCl$. Oxoacids of Phosphorus Hypophosphorous acid ($H_3PO_2$): Monobasic, reducing agent. Structure: $P-H$ bonds (2), $P-OH$ (1). Phosphorous acid ($H_3PO_3$): Dibasic, reducing agent. Structure: $P-H$ bond (1), $P-OH$ (2). Orthophosphoric acid ($H_3PO_4$): Tribasic, stable. Structure: $P-OH$ (3). Group 16 Elements (Oxygen Family) General Electronic Configuration: $ns^2 np^4$ Oxidation States: $-2, +2, +4, +6$. Oxygen shows $-2, -1, +1, +2$. Anomalous behaviour of Oxygen: Small size, high electronegativity, absence of d-orbitals. Forms $p\pi-p\pi$ multiple bonds. Hydrides: $H_2O, H_2S, H_2Se, H_2Te$. Thermal stability decreases down the group. Acidic character increases. $H_2O$ is liquid due to H-bonding. Oxides: Dioxides ($EO_2$) and trioxides ($EO_3$). Acidic character decreases down the group. Halides: $EX_2, EX_4, EX_6$. Stability of halides decreases with increase in size of halogen. Dioxygen ($O_2$) Preparation: Thermal decomposition of oxygen-containing salts ($KClO_3, KMnO_4, K_2Cr_2O_7$). Properties: Paramagnetic. Reacts with metals and non-metals. Uses: Respiration, combustion, welding. Ozone ($O_3$) Preparation: $3O_2(g) \xrightarrow{Silent~electric~discharge} 2O_3(g)$ Properties: Blue-black gas, diamagnetic. Powerful oxidizing agent. Depletes ozone layer ($O_3 + CFCs \rightarrow O_2 + ClO$). Structure: Angular, two $O-O$ bond lengths are identical (resonance hybrid). Sulphur (S) Allotropic forms: Rhombic (alpha-sulphur, stable at room temp), Monoclinic (beta-sulphur, stable above 369 K). Both have $S_8$ puckered ring structure. Sulphur Dioxide ($SO_2$) Preparation: $S + O_2 \rightarrow SO_2$. $4FeS_2 + 11O_2 \rightarrow 2Fe_2O_3 + 8SO_2$. Properties: Colourless gas, pungent smell. Acidic oxide. Reducing agent (in presence of moisture). Uses: Bleaching agent, disinfectant, preservative. Sulphuric Acid ($H_2SO_4$) Preparation (Contact Process): $S + O_2 \rightarrow SO_2$ (or $FeS_2$ roasting) $2SO_2(g) + O_2(g) \xrightarrow{V_2O_5~catalyst} 2SO_3(g)$ ($\Delta H = -196.6~kJ/mol$) $SO_3 + H_2SO_4 \rightarrow H_2S_2O_7$ (Oleum) $H_2S_2O_7 + H_2O \rightarrow 2H_2SO_4$ Properties: Strong acid, dehydrating agent, oxidizing agent. $C_{12}H_{22}O_{11} \xrightarrow{Conc.~H_2SO_4} 12C + 11H_2O$ (charring sugar) Uses: Fertilizers, detergents, chemicals, petroleum refining. Group 17 Elements (Halogen Family) General Electronic Configuration: $ns^2 np^5$ Oxidation States: $-1, +1, +3, +5, +7$. Fluorine always $-1$. Physical Properties: $F_2$ (yellow gas), $Cl_2$ (greenish-yellow gas), $Br_2$ (reddish-brown liquid), $I_2$ (violet solid). Bond Dissociation Enthalpy: $Cl_2 > Br_2 > F_2 > I_2$ (due to lone pair-lone pair repulsion in $F_2$). Electronegativity: $F > Cl > Br > I$. Reactivity: $F_2$ is most reactive. Reactivity decreases down the group. Reactivity towards Hydrogen: $HX$ acids. Acidic strength: $HF HCl > HBr > HI$. Reactivity towards Oxygen: Halogens form various oxides, generally unstable. Reactivity towards Metals: Form metal halides ($MX, MX_2, MX_3$, etc.). Ionic character $MF > MCl > MBr > MI$. Reactivity towards Other Halogens: Form interhalogen compounds (e.g., $ClF, BrF_3, IF_5, IF_7$). Chlorine ($Cl_2$) Preparation (Deacon's Process): $4HCl(g) + O_2(g) \xrightarrow{CuCl_2,~723K} 2Cl_2(g) + 2H_2O(g)$ Electrolytic Process: Electrolysis of brine solution ($2NaCl(aq) + 2H_2O(l) \rightarrow 2NaOH(aq) + Cl_2(g) + H_2(g)$). Properties: Greenish-yellow gas. Oxidizing agent, bleaching agent (in presence of moisture). Reaction with $NaOH$: Cold, dilute: $2NaOH + Cl_2 \rightarrow NaCl + NaOCl + H_2O$ Hot, concentrated: $6NaOH + 3Cl_2 \rightarrow 5NaCl + NaClO_3 + 3H_2O$ Uses: Bleaching, sterilization, PVC, CFCs. Hydrogen Chloride ($HCl$) Preparation: $NaCl + H_2SO_4 \xrightarrow{420K} NaHSO_4 + HCl$. $NaHSO_4 + NaCl \xrightarrow{823K} Na_2SO_4 + HCl$. Properties: Colourless, pungent gas. Forms constant boiling azeotrope with water. Aqua Regia: $3$ parts conc. $HCl$ and $1$ part conc. $HNO_3$. Dissolves noble metals. $Au + 4H^+ + NO_3^- + 4Cl^- \rightarrow [AuCl_4]^- + NO + 2H_2O$. Oxoacids of Halogens Stability and acidic strength increase with increase in oxidation state of halogen. $HClO$ (Hypochlorous acid) - $+1$ $HClO_2$ (Chlorous acid) - $+3$ $HClO_3$ (Chloric acid) - $+5$ $HClO_4$ (Perchloric acid) - $+7$ (Strongest acid) Group 18 Elements (Noble Gases) General Electronic Configuration: $ns^2 np^6$ (He: $1s^2$) Properties: Monoatomic, colourless, odourless, tasteless. Very low melting/boiling points. Unreactive due to stable electron configuration. Ionization Enthalpy: Very high. Electron Gain Enthalpy: Positive. Helium (He): Non-inflammable, light gas. Used in balloons, diving apparatus. Neon (Ne): Neon signs. Argon (Ar): Filling electric bulbs. Xenon (Xe): Forms compounds due to lower ionization enthalpy. $XeF_2$: Linear $XeF_4$: Square planar $XeF_6$: Distorted octahedral $XeO_3$: Pyramidal $XeOF_4$: Square pyramidal Krypton (Kr) and Radon (Rn): Used in some specialized applications. Radon is radioactive.