P-Block Elements Revision

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Boron Family (Group 13) Elements: Boron (B), Aluminium (Al), Gallium (Ga), Indium (In), Thallium (Tl), Nihonium (Nh). Boron is a non-metal, Aluminium is a metal (some non-metallic properties). Ga, In, Tl are metallic. Occurrence: Boron: Orthoboric acid ($\text{H}_3\text{BO}_3$), Borax ($\text{Na}_2\text{B}_4\text{O}_7 \cdot 10\text{H}_2\text{O}$), Kernite ($\text{Na}_2\text{B}_4\text{O}_7 \cdot 4\text{H}_2\text{O}$). Aluminium: Bauxite ($\text{Al}_2\text{O}_3 \cdot 2\text{H}_2\text{O}$), Cryolite ($\text{Na}_3\text{AlF}_6$). Isotopes of Boron: $^{10}\text{B}$ (19%), $^{11}\text{B}$ (81%). Aluminium is the most abundant metal (8.3% by mass) and 3rd most abundant element in Earth's crust after Oxygen (45.5%) and Si (27.7%). Boron Compounds and Reactions Orthoboric Acid ($\text{H}_3\text{BO}_3$) Formula: $\text{B}(\text{OH})_3$ Complexes with glycerol. Heating: $\text{H}_3\text{BO}_3 \xrightarrow{\Delta} \text{HBO}_2$ (Metaboric acid) $\text{HBO}_2 \xrightarrow{\Delta} \text{B}_2\text{O}_3$ (Boron trioxide) Diborane ($\text{B}_2\text{H}_6$) Preparation: Industrial: $2\text{BF}_3 + 6\text{NaH} \xrightarrow{450K} \text{B}_2\text{H}_6 + 6\text{NaF}$ Lab (small scale): $2\text{NaBH}_4 + \text{I}_2 \rightarrow \text{B}_2\text{H}_6 + 2\text{NaI} + \text{H}_2$ From $\text{BF}_3$: $3\text{BF}_3 + 3\text{LiAlH}_4 \rightarrow 2\text{B}_2\text{H}_6 + 3\text{LiF} + 3\text{AlF}_3$ Silent electric discharge: $2\text{BCl}_3 + 6\text{H}_2 \rightarrow \text{B}_2\text{H}_6 + 6\text{HCl}$ Properties: Colourless, highly toxic gas. Boiling point: 180 K. Catches fire spontaneously in air: $\text{B}_2\text{H}_6 + 3\text{O}_2 \rightarrow \text{B}_2\text{O}_3 + 3\text{H}_2\text{O}$ Carbon Family (Group 14) Reactivity Towards Halogens Elements form two series of halides: $\text{MX}_2$ and $\text{MX}_4$. Generally, halides are covalent and $\text{sp}^3$ hybridized, except $\text{SnF}_4$ and $\text{PbF}_4$ which are ionic. $\text{PbI}_4$ does not exist. Order of thermal stability: $\text{CX}_4 > \text{SiX}_4 > \text{GeX}_4 > \text{SnX}_4 > \text{PbX}_4$. Except for $\text{CCl}_4$, other tetrachlorides are readily hydrolysed. Example: $\text{SiCl}_4 + 4\text{H}_2\text{O} \rightarrow \text{Si}(\text{OH})_4 + 4\text{HCl}$ (Silicic acid) This is due to the ability of Si to accommodate lone pair of electrons from oxygen in its d-orbitals. Nitrogen Family (Group 15) Preparation of Dinitrogen ($\text{N}_2$) Colourless, odourless, tasteless & non-toxic gas. Commercial production: Liquefaction and fractional distillation of air. Lab method: $\text{NH}_4\text{Cl}(\text{aq}) + \text{NaNO}_2(\text{aq}) \xrightarrow{\Delta} \text{N}_2(\text{g}) + 2\text{H}_2\text{O}(\text{l}) + \text{NaCl}(\text{aq})$ Small amounts of NO and $\text{HNO}_3$ are also formed, removed by passing gas through $\text{H}_2\text{SO}_4$. $\text{NH}_4\text{Cr}_2\text{O}_7 \xrightarrow{\text{heat}} \text{N}_2(\text{g}) + 4\text{H}_2\text{O}(\text{g}) + \text{Cr}_2\text{O}_3(\text{s})$ (Volcano reaction) Very pure nitrogen: $\text{Ba}(\text{N}_3)_2 \xrightarrow{\Delta} \text{Ba} + 3\text{N}_2$ $2\text{NaN}_3 \xrightarrow{\Delta} 2\text{Na} + 3\text{N}_2$ Reactions of Nitrogen: With metals (nitrides): $6\text{Li} + \text{N}_2 \xrightarrow{\text{heat}} 2\text{Li}_3\text{N}$ $3\text{Mg} + \text{N}_2 \xrightarrow{\text{heat}} \text{Mg}_3\text{N}_2$ With non-metals: $\text{N}_2(\text{g}) + 3\text{H}_2(\text{g}) \xrightleftharpoons[\text{catalyst: Fe/Mo}]{773K, 200 atm} 2\text{NH}_3(\text{g})$ ($\Delta \text{H} = -46.1 \text{ kJ/mol}$) (Haber's Process) $\text{N}_2(\text{g}) + \text{O}_2(\text{g}) \xrightarrow{2000K} 2\text{NO}(\text{g})$ Nitric Acid ($\text{HNO}_3$) or Aqua Fortis Lab method: $\text{NaNO}_3 + \text{H}_2\text{SO}_4 \rightarrow \text{NaHSO}_4 + \text{HNO}_3$ Ostwald's Process (Manufacture): Catalytic oxidation of ammonia: $4\text{NH}_3(\text{g}) + 5\text{O}_2(\text{g}) \xrightarrow{\text{Pt/Rh gauge catalyst}, 500K, 9 bar} 4\text{NO}(\text{g}) + 6\text{H}_2\text{O}(\text{g})$ Oxidation of NO: $2\text{NO}(\text{g}) + \text{O}_2(\text{g}) \rightarrow 2\text{NO}_2(\text{g})$ Absorption of $\text{NO}_2$ in water: $3\text{NO}_2(\text{g}) + \text{H}_2\text{O}(\text{l}) \rightarrow 2\text{HNO}_3(\text{aq}) + \text{NO}(\text{g})$ (NO is recycled) Aqueous $\text{HNO}_3$ can be concentrated to ~68% by mass by distillation. Further concentration to 98% can be achieved by dehydration with concentrated $\text{H}_2\text{SO}_4$. Properties: Colourless liquid (b.p. 355.6 K). Lab grade contains 68% $\text{HNO}_3$ by mass. Oxygen Family (Group 16) Elements: Oxygen (O), Sulphur (S), Selenium (Se), Tellurium (Te), Polonium (Po), Livermorium (Lv). Collectively known as Chalcogens. Oxygen is the most abundant element on Earth (46.6% of Earth's crust by mass). Air contains 20.946% Oxygen by volume. Sulphur occurrence (combined state): Gypsum: $\text{CaSO}_4 \cdot 2\text{H}_2\text{O}$ Epsom salt: $\text{MgSO}_4 \cdot 7\text{H}_2\text{O}$ Baryte: $\text{BaSO}_4$ Galena: $\text{PbS}$ Zinc blende: $\text{ZnS}$ Copper pyrites: $\text{CuFeS}_2$ Sulphur is also found in organic materials like eggs, proteins, garlic, onion, mustard, hair, wool. General electronic configuration: $\text{ns}^2 \text{np}^4$. Chemical Reactions of Dioxygen ($\text{O}_2$) $2\text{Ca} + \text{O}_2 \rightarrow 2\text{CaO}$ $4\text{Al} + 3\text{O}_2 \rightarrow 2\text{Al}_2\text{O}_3$ $\text{P}_4 + 5\text{O}_2 \rightarrow \text{P}_4\text{O}_{10}$ $\text{C} + \text{O}_2 \rightarrow \text{CO}_2$ $2\text{ZnS} + 3\text{O}_2 \rightarrow 2\text{ZnO} + 2\text{SO}_2$ $\text{CH}_4 + 2\text{O}_2 \rightarrow \text{CO}_2 + 2\text{H}_2\text{O}$ $2\text{SO}_2 + \text{O}_2 \xrightarrow{\text{V}_2\text{O}_5} 2\text{SO}_3$ $4\text{HCl} + \text{O}_2 \xrightarrow{\text{CuCl}_2} 2\text{Cl}_2 + 2\text{H}_2\text{O}$ Uses of Oxygen Normal respiration and combustion processes. Oxyacetylene welding. Manufacturing steel. In combustion of fuels (e.g., hydrazines in liquid oxygen provides thrust in rockets). Halogen Family (Group 17) Reactivity Towards Oxygen Fluorine forms two oxides: $\text{OF}_2$ and $\text{O}_2\text{F}_2$. $\text{OF}_2$ is stable at 298 K. $\text{OF}_2$ oxidises Plutonium to $\text{PuF}_6$, used in removing Plutonium from spent nuclear fuel. General decreasing order of stability of oxides formed by halogens (I > Cl > Br). Iodine oxides are more stable due to high polarizability of iodine. Chlorine oxides are stable due to multiple bond formation between Cl and O (availability of d-orbitals). Bromine lacks both characteristics, hence stability of its oxides is least. Bromine oxides exist only at low temperatures and are very powerful oxidising agents. Oxides of iodine ($\text{I}_2\text{O}_4$, $\text{I}_2\text{O}_5$, $\text{I}_2\text{O}_7$) are insoluble solids and decompose on heating. $\text{I}_2\text{O}_5$ is a very good oxidising agent.