Period 3 Elements & Oxides PDF - A Level Chemistry - AQA

A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES Period 3 Elements: Na Mg Al Si P S Cl Ar PERIOD 3 ELEMENTS +WATER Learn these equations and...

A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES Period 3 Elements: Na Mg Al Si P S Cl Ar PERIOD 3 ELEMENTS +WATER Learn these equations and observations! Na: Na(s) + H2O(l) → NaOH(aq) + H2(g) This is a reaction you should know all by now. It produces an alkaline solution. Mg: Mg(s) + 2H2O(l) → Mg(OH)(s) + H2(g) Mg reacts very slowly with liquid water to produce insoluble Mg(OH)2. This appears as a white precipitate. Mg(s) + H2O(g) → MgO(s) + H2(g) Mg reacts faster with steam to produce MgO. This appears as a white powder. Cl2: Cl2(g) + H2O(l) → HClO(aq) + HCl(aq) This is Year 12 revision. Cl2 undergoes a disproportionation reaction where it is simultaneously oxidised and reduced. Al, Si, P, S and Ar do not react with water AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES 3.2.4 PERIOD 3 ELEMENTS & OXIDES Learn these equations, products and observations! When these elements are “burned” in excess oxygen… Element Equation Observations Yellow Flame Na2O Na 4Na(s) + O2(g) → 2Na2O(s) Appearance: White solid Bonding: Ionic Character: Basic White Flame MgO Mg 2Mg(s) + O2(g) → 2MgO(s) Appearance: White solid / smoke Bonding: Ionic Character: Basic White Flame Al2O3 Appearance: White solid Al 4Al(s) + 3O2(g) → 2Al2O3(s) Bonding: Ionic Character: Amphoteric (reacts with acids& bases) White Flame SiO2 Si Si(s) + O2(g) → SiO2(s) Appearance: White solid Bonding: Ionic Character: Acidic Yellow Flame P4O10 P P4(s) + 5O2(g) → P4O10(s) Appearance: White solid Bonding: Giant Covalent Character: Acidic S(s) + O2(g) → SO2(g) Blue Flame SO2 SO2 can react further with O2 in the Appearance: Pungent gas S presence of a V2O5 catalyst, as in the Bonding: Simple Covalent contact process… Character: Acidic 2SO2(g) + O2(g) ⇌ SO3(g) Notice that metal oxides are ionic and basic and non-metal oxides are covalent and acidic! More on aluminium oxide and “amphoterism” later. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES MELTING POINTS OF PERIOD 3 OXIDES GIANT IONIC SIMPLE COVALENT COVALENT Na2O MgO Al2O3 SiO2 P4O10 SO3 3000 2250 1500 750 0 -750 MgO has a greater melting point than SiO2 has a high melting point as the Na2O as it has a greater charge of the string covalent binds must be broken in cation (2+), causing a stronger order to melt it. electrostatic attraction between the Both P4O10 and SO3 have very Lowe ions. melting points as they are simple Despite the cation in Al2O3 having a 3+ covalent. It is only the weak charge, it has a lower melting point intermolecular forces that are broken than MgO as it shows “covalent when they melt. P4O10 contains more character” (See Thermochemistry) electrons than SO3, so the induced dipole forces are stronger. Hence it has a higher melting point. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES PERIOD 3 OXIDES + WATER Learn these equations, products and observations! When these elements are “burned” in excess oxygen… pH of Element Equation Observations Product Na2O Na2O(s) + H2O(l) → 2NaOH(aq) 13 Highly exothermic reaction Mg(OH)2 insoluble, so white MgO MgO(s) + H2O(l) → Mg(OH)2(s) 9 precipitate observed Al2O3 NO REACTION 7 Both insoluble & unreactive due to covalent character SiO2 NO REACTION 7 Highly exothermic reaction P4O10 P4O10s) + 6H2O(l) → 4H3PO4(aq) 0 Phosphoric acid produced which is a weak acid Sulfurous acid formed which is a SO2 SO2(g) + H2O(l) → H2SO3(aq) 3 weak acid Sulfuric acid produced which is a SO3 SO3(g) + H2O(l) → H2SO4(aq) 0 strong acid Notice the trend in the pH of the solutions formed. How the metal oxides produce an alkaline solution and the non-metal oxides produce an acidic solution. You need to know the structures and information about these acids. See next page. AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES ACIDS FROMED BY PERIOD 3 OXIDES Tetrahedral Triprotic weak acid O When in (aq) each H+ dissociates individually, so each has it’s own Ka value H3PO4 P H3PO4 ⇌ H2PO4- ⇌ HPO42- ⇌ PO43- HO OH H+ H+ H+ OH Each dissociation becomes increasingly less likely so Ka increases Trigonal Pyramidal Diprotic weak acid ·· S When in (aq) each H+ dissociates individually, so each has it’s own Ka value H2SO3 HO O H2SO3 ⇌ HSO3- ⇌ SO32- OH H+ H+ Each dissociation becomes increasingly less likely so Ka increases O Tetrahedral Diprotic strong acid H2SO4 When in (aq) both H+ ions dissociate S fully. HO O H2SO4 → 2H+ + SO42- OH AQA www.chemistrycoach.co.uk © scidekick ltd 2024 A LEVEL CHEMISTRY 3.2.4 PERIOD 3 ELEMENTS & OXIDES PERIOD 3 OXIDES | NEUTRALISATION Learn these reactions and equations. Of course, be prepared to use different acids and bases in the equations. Metal Oxides are basic, so neutralise acids to produce a salt and water e.g. Na2O(s) + 2HCl(aq) → 2NaCl(aq) + H2O(l) MgO(s) + 2HCl(aq) → MgCl2(aq) + H2O(l) Aluminium Oxide is amphoteric. This means it can react with acids and bases. Al2O3(s) + 6HCl(aq) → 2AlCl3(aq) + 3H2O(l) Al2O3(s) + 2NaOH(aq) + 3H2O → 2Na+[Al(OH)4]- “aluminate” Non-Metal Oxides are acidic, so neutralise bases to produce a salt and water e.g. SiO2(s) + 2NaOH(aq) → Na2SiO3(aq) + H2O(l) “silicate” P4O10(s) + 12NaOH(aq) → 4Na3PO4(aq) + 6H2O(l) “phosphate” SO2(g) + 2NaOH(aq) → Na2SO3(aq) + H2O(l) “sulfite” SO2(s) + 2NaOH(aq) → Na2SO4(aq) + H2O(l) “sulfate” AQA www.chemistrycoach.co.uk © scidekick ltd 2024