13.1 REACTIONS OF PERIOD 3 ELEMENTS GROUP 3

13.1 REACTIONS OF PERIOD 3 ELEMENTS Atomic Radius – Decreases across period Extra protons pull electrons closer No extra shielding Melting/Boiling Point Increase up to silicon then decrease Metallic bonding in Na, Mg and Al Macromolecular tetrahedral structure in Si P, S, Cl are all molecular – M.P & B.P depend on VdW Ar exists as individual atoms First Ionisation Energy -

13.1 REACTIONS OF PERIOD 3 ELEMENTS REACTIONS WITH WATER Sodium: Reacts vigorously forming a molten ball on the surface, fizzing and producing H2 gas 2Na(s) + 2H2O(l)  2NaOH(aq) + H2(g) Magnesium: Reacts slowly with no visible reaction It forms a weakly alkaline solution  how we know it reacts Mg(s) + 2H2O(l)  Mg(OH)2(aq) + H2(g)

13.1 REACTIONS OF PERIOD 3 ELEMENTS WHY DOES SODIUM REACT MORE? When they react: Na loses 1 electron Mg loses 2 electrons It takes less energy to remove 1 electron than it does 2 More energy (usually heat) is needed for Mg to react Mg(OH)2 is not very soluble in water, so produces relatively few OH- ions. This makes it a weaker alkali than NaOH

13.1 REACTIONS OF PERIOD 3 ELEMENTS REACTIONS WITH OXYGEN Element Oxide Oxidation State of Element Extent of Reaction Flame Na Na2O +1 Vigorous Yellow Mg MgO +2 Brilliant White Al Al2O3 +3 Slow N/A Si SiO2 +4 P P4O10 +5 One allotrope* spontaneously combusts; the other requires heating S SO2 Burns steadily Blue *Allotrope: same element but atoms arranged differently

13.2 OXIDES OF ELEMENTS IN PERIOD 3 TRENDS IN THE PHYSICAL PROPERTIES Metal Oxides  Na2O, MgO & Al2O3 High melting points  giant ionic lattices Strong forces of attraction between each ion Lots of heat energy required to break bonds MgO is higher than Na2O because 2+ ions attract O2- ions more strongly than 1+ sodium ions Al2O3 is lower than expected because 3+ ions are small with a high charge  this distorts oxygen’s electron cloud making the bond partially covalent

13.2 OXIDES OF ELEMENTS IN PERIOD 3 TRENDS IN THE PHYSICAL PROPERTIES Non-metal Oxides  SiO2, P4O10 & SO2 SiO2 is highest of non-metal oxides:  forms a giant macromolecular structure.  Strong bonds that require lots of energy to be broken P4O10 & SO2 are simple covalent molecules.  Weak intermolecular forces  Dipole-Dipole forces  Van der Waals forces

13.2 OXIDES OF ELEMENTS IN PERIOD 3 Ionic oxides of Na & Mg dissolve to form hydroxides Form alkaline solutions Sodium hydroxide is more soluble in water, so forms a more alkaline solution than magnesium hydroxide Na2O(s) + H2O(l)  2NaOH(aq) pH 12-14 MgO(s) + H2O(l)  Mg(OH)2(aq) pH 9-10

13.2 OXIDES OF ELEMENTS IN PERIOD 3 Simple covalent oxides (P and S) form acidic solutions Phosphorous (V) oxide reacts violently to form phosphoric acid: P4O10(s) + 6H2O(l)  4H3PO4 (aq)  This ionises: 4H3PO4 (aq) H+(aq) + H2PO4-(aq) Sulphur dioxide reacts to form sulphuric (IV) acid: SO2(g) + H2O(l)  H2SO3(aq)  partially dissociates H2SO3 (aq) H+(aq) + HSO3-(aq)

13.2 OXIDES OF ELEMENTS IN PERIOD 3 Giant covalent structure of silicon dioxide means it is insoluble. It will react with bases to form salts so is classed as acidic Aluminium oxide is also insoluble. It will react with acids AND bases to form salts. i.e. it can act as an acid OR a base  AMPHOTERIC Sulphur trioxide reacts violently to form sulphuric (VI) acid: SO3(g) + H2O(l)  H2SO4(aq)  H+(aq) + HSO4-(aq)

13.3 OXIDES WITH ACIDS & BASES pH OF PERIOD 3 OXIDES: P4O10 MgO SO2 Al2O3 Na2O SiO2 SO3

13.3 OXIDES WITH ACIDS & BASES A CLASSIC The equation for neutralising an acid with a base is a classic Acid + Base  Salt + Water It’s no different for Period 3 oxides You will be expected to write the equations

13.3 OXIDES WITH ACIDS & BASES SODIUM & MAGNESIUM: These oxides are basic so will neutralise acids. E.g. Sodium oxide reacts with hydrochloric acid to form Sodium chloride and water Na2O(s) + 2HCl(aq)  2NaCl(aq) + H2O(l) E.g. Magnesium oxide reacts with sulphuric acid to form magnesium sulphate and water MgO(s) + H2SO4(aq)  MgSO4(aq) + H2O(l)

13.3 OXIDES WITH ACIDS & BASES ALUMINIUM OXIDE: This is an amphoteric oxide  it can react with both acids and alkalis E.g. With sulphuric acid, aluminium sulphate is formed Al2O3(s) + 3H2SO4(aq)  Al2(SO4)3 (aq) + 3H2O(l) E.g. With hot, concentrated sodium hydroxide, sodium aluminate is formed Al2O3(s) + 2NaOH(aq) + 3H2O(l)  2NaAl(OH)4(aq)

13.3 OXIDES WITH ACIDS & BASES SILICON, PHOSPHOROUS & SULPHUR: These oxides are all acidic so will neutralise bases SiO2(s) + 2NaOH(aq)  Na2SiO3(aq) + H2O(l) P4O10(s) + 12NaOH(aq)  4Na3PO4(aq) + 6H2O(l) SO2(g) + 2NaOH(aq)  Na2SO3(aq) + H2O(l) SO3(g) + 2NaOH(aq)  Na2SO4(aq) + H2O(l) Phosphorous (V) Oxide (Phosphorous pentoxide) is actually more complicated than this. Read the bottom of page 192 and write out the steps. Start by reacting P4O10 with H2O Lewis Acids  electron pair acceptors Lewis Bases  An electron pair donor