9. The Periodic Table: chemical periodicity
A section of Chemistry, 9701
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Phosphorus is a reactive Period3 element. Phosphorus has several allotropes. Details of two allotropes are given. allotrope of phosphorus formula melting point / °C white P4 red P White phosphorus and red phosphorus both have covalent bonding. Suggest the types of structure shown by white phosphorus (P4) and red phosphorus (P). Explain why red phosphorus (P) has a higher melting point than white phosphorus (P4). structure of P4 structure of P explanation  Red phosphorus (P) forms when white phosphorus (P4) is exposed to sunlight. 4 P4→ P∆H = –17.6 kJ mol–1 white red Use this information to draw a reaction pathway diagram to show the formation of red phosphorus (P) from white phosphorus (P4). enthalpy progress of reaction P4  Some reactions of P4are shown in the reaction scheme. P4PCl 5excess Cl 2excess O2P4O10Q reaction 2 H2OH2Oreaction 1 State the oxidation number of phosphorus in P4O10. Deduce the identity of Q and hence construct chemical equations for reactions 1 and 2. reaction 1 PCl 5 + H2O → reaction 2 P4O10 + H2O →  Triphenylphosphine is used in a type of reaction known as a Wittig reaction. P triphenylphosphine where = –C6H5 Give the empirical formula of triphenylphosphine. In a Wittig reaction, an aldehyde reacts with a halogenoalkane to form an alkene. The conversion is shown in the following unbalanced equation. O + H R1 R2 R2 I R1 H triphenylphosphine strong base CompoundH can be made from propanal, C2H5CHO. Stage3 in the reaction scheme is a Wittig reaction. stage 1 C2H5CHO G triphenylphosphine NaBH4 stage 2 G C2H5CH2I stage 3 (Wittig reaction) H C2H5CH2I + C2H5CHO red phosphorus and I2 strong base State the types of reaction that occur in stages 1 and 2. stage 1 stage 2  Draw the structures of G and H in the boxes provided. G H  Identify the organic products formed when compound J, shown below, is heated with hot concentrated acidified manganate(ions. hot concentrated MnO4 – H2SO4 J  
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THEORY
2021
Paper 2, Variant 1
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Phosphorus is a reactive Period3 element. Phosphorus has several allotropes. Details of two allotropes are given. allotrope of phosphorus formula melting point / °C white P4 red P White phosphorus and red phosphorus both have covalent bonding. Suggest the types of structure shown by white phosphorus (P4) and red phosphorus (P). Explain why red phosphorus (P) has a higher melting point than white phosphorus (P4). structure of P4 structure of P explanation  Red phosphorus (P) forms when white phosphorus (P4) is exposed to sunlight. 4 P4→ P∆H = –17.6 kJ mol–1 white red Use this information to draw a reaction pathway diagram to show the formation of red phosphorus (P) from white phosphorus (P4). enthalpy progress of reaction P4  Some reactions of P4are shown in the reaction scheme. P4PCl 5excess Cl 2excess O2P4O10Q reaction 2 H2OH2Oreaction 1 State the oxidation number of phosphorus in P4O10. Deduce the identity of Q and hence construct chemical equations for reactions 1 and 2. reaction 1 PCl 5 + H2O → reaction 2 P4O10 + H2O →  Triphenylphosphine is used in a type of reaction known as a Wittig reaction. P triphenylphosphine where = –C6H5 Give the empirical formula of triphenylphosphine. In a Wittig reaction, an aldehyde reacts with a halogenoalkane to form an alkene. The conversion is shown in the following unbalanced equation. O + H R1 R2 R2 I R1 H triphenylphosphine strong base CompoundH can be made from propanal, C2H5CHO. Stage3 in the reaction scheme is a Wittig reaction. stage 1 C2H5CHO G triphenylphosphine NaBH4 stage 2 G C2H5CH2I stage 3 (Wittig reaction) H C2H5CH2I + C2H5CHO red phosphorus and I2 strong base State the types of reaction that occur in stages 1 and 2. stage 1 stage 2  Draw the structures of G and H in the boxes provided. G H  Identify the organic products formed when compound J, shown below, is heated with hot concentrated acidified manganate(ions. hot concentrated MnO4 – H2SO4 J  
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THEORY
2021
Paper 2, Variant 3
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Some of the common chlorides of Period3 elements are shown in the list. NaCl MgCl 2 Al Cl 3 SiCl 4 PCl 5 From this list, identify: all the chlorides that have giant ionic structures in the solid state all the chlorides that react vigorously with water to form strongly acidic solutions the chloride that dissolves in water to form a neutral solution the chloride formed from the element with the highest melting point. NaCl is one product of the reaction of chlorine gas and cold aqueous sodium hydroxide. Identify the other products. PCl 5 reacts with alcohols to form chloroalkanes. Identify this type of reaction. Draw the structure of the organic product formed in the reaction of an excess of PCl 5 with butane-1,3-diol.  Sulfur, S8, reacts with chlorine to form several different chlorides. The most common are S2Cl 2 and SCl 2. SCl 2 forms when sulfur reacts with an excess of chlorine. reaction1 S8+ 4Cl 2→ 4S2Cl 2∆Hr = –58.2 kJ mol–1 reaction2 S2Cl 2+ Cl 22SCl 2∆Hr = –40.6 kJ mol–1 SCl 2 is a cherry-red liquid that reacts vigorously with water to form an acidic solution. Use this information to deduce the bonding and structure shown by SCl 2. Explain your answer. Calculate the enthalpy change of formation, ∆Hf, of SCl 2. You may find it useful to use Hess’s Law to construct an energy cycle.  enthalpy change of formation of SCl 2, ∆Hf = kJ mol–1  State the effect of a decrease in pressure on the position of equilibrium in reaction2. Explain your answer. Fig.3.1 shows the two structural isomers of S2Cl 2. isomer I isomer II Cl Cl S S Cl Cl S S Define the term structural isomer. Suggest a value for the Cl –S–S bond angle in isomerI. Explain your answer. bond angle = ° explanation  Draw a dot-and-cross diagram to show the bonding in isomerII. Show outer shell electrons only.  
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THEORY
2022
Paper 2, Variant 1
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The chlorides of some of the Period3 elements are shown in Table2.1. Table 2.1 Period 3 chloride NaCl Al Cl 3 SiCl 4 PCl 5 PCl 3 SCl 2 bonding C C structure S S oxidation state of Period 3 element Complete Table 2.1. ● Identify the bonding shown by each chloride under standard conditions. Use C = covalent, I = ionic, M = metallic. ● Identify the structure shown by each chloride under standard conditions. Use G = giant, S = simple. ● Deduce the oxidation state of the Period 3 element in each chloride.  Write equations for the reactions of NaCl and PCl 5 with water. Include state symbols in both equations. NaCl PCl 5  In the gas phase, Al Cl 3exists at equilibrium with Al 2Cl 6as shown. equation 1 2Al Cl 3Al 2Cl 6∆Hr = –63 kJ mol–1 Complete the dot-and-cross diagram to show the bonding in Al 2Cl 6. Al Cl Cl  State the effect of an increase in temperature on the equilibrium mixture in equation1. Explain your answer. A 3.30 g sample of a Period3 chloride is heated to 500 K in a sealed flask. At this temperature, the chloride is a gas of volume 250 cm3 and the pressure in the flask is 323 kPa. Use the ideal gas equation pV = nRT to calculate the Mr of the Period3 chloride. Deduce its formula.  Mr =  formula of Period 3 chloride =  An excess of Cl –is added to 1 cm3 of Br2. Describe what is observed. Explain your answer. SCl 2 has Mr = 103.1 and is a liquid at room temperature. SBr2 has Mr = 191.9 and is a gas at room temperature. Explain the difference in the physical state of SCl 2 and SBr2. Give your answer in terms of intermolecular forces. Bismuth is a dense metal in the same group as phosphorus. Draw a labelled diagram to show the bonding in bismuth metal.  Bismuth reacts with chlorine to form BiCl 3. BiCl 3 is a solid at room temperature. It melts when heated gently. BiCl 3 reacts vigorously with water at room temperature to form an acidic solution. Suggest the type of bonding and structure shown by BiCl 3. Explain your answer. 
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THEORY
2022
Paper 2, Variant 2
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Some of the common chlorides of Period3 elements are shown in the list. NaCl MgCl 2 Al Cl 3 SiCl 4 PCl 5 From this list, identify: all the chlorides that have giant ionic structures in the solid state all the chlorides that react vigorously with water to form strongly acidic solutions the chloride that dissolves in water to form a neutral solution the chloride formed from the element with the highest melting point. NaCl is one product of the reaction of chlorine gas and cold aqueous sodium hydroxide. Identify the other products. PCl 5 reacts with alcohols to form chloroalkanes. Identify this type of reaction. Draw the structure of the organic product formed in the reaction of an excess of PCl 5 with butane-1,3-diol.  Sulfur, S8, reacts with chlorine to form several different chlorides. The most common are S2Cl 2 and SCl 2. SCl 2 forms when sulfur reacts with an excess of chlorine. reaction1 S8+ 4Cl 2→ 4S2Cl 2∆Hr = –58.2 kJ mol–1 reaction2 S2Cl 2+ Cl 22SCl 2∆Hr = –40.6 kJ mol–1 SCl 2 is a cherry-red liquid that reacts vigorously with water to form an acidic solution. Use this information to deduce the bonding and structure shown by SCl 2. Explain your answer. Calculate the enthalpy change of formation, ∆Hf, of SCl 2. You may find it useful to use Hess’s Law to construct an energy cycle.  enthalpy change of formation of SCl 2, ∆Hf = kJ mol–1  State the effect of a decrease in pressure on the position of equilibrium in reaction2. Explain your answer. Fig.3.1 shows the two structural isomers of S2Cl 2. isomer I isomer II Cl Cl S S Cl Cl S S Define the term structural isomer. Suggest a value for the Cl –S–S bond angle in isomerI. Explain your answer. bond angle = ° explanation  Draw a dot-and-cross diagram to show the bonding in isomerII. Show outer shell electrons only.  
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THEORY
2022
Paper 2, Variant 3
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