METALLIC AND NON-METALLIC OXIDES

OXIDES OF PERIOD 3 ELEMENTS SUMMARY Na2O MgO Al2O3 SiO2 SO2 Melting point / K 1548 3125 2345 1923 200 bonding ionic ionic ionic/cov covalent covalent structure giant giant giant giant simple lattice lattice lattice molecular molecular classification basic basic amphoteric acidic acidic solubility very sparingly insoluble insoluble reacts in water solution pH 14 9 3

OXIDES OF PERIOD 3 ELEMENTS PREPARATION • metals produce basic oxides • non-metals produce acidic oxides • aluminium oxide is an amphoteric oxide (acidic and basic properties) • ionic oxides have high melting points • ionic oxides conduct electricity when molten • most oxides can be prepared by direct combination (EXC. SO3) 2Mg(s) + O2(g) ——> 2MgO(s) 4Al(s) + 3O2(g) ——> 2Al2O3(s) S(s) + O2(g) ——> SO2(g) +2 -2 +3 -2 +4 -2

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES Na2O • white solid • giant ionic lattice • soluble in water to form a strongly alkaline solution (pH = 13-14) Na2O(s) + H2O(l) ——> 2NaOH(aq) • reacts with acids to form salts – A BASIC OXIDE Na2O(s) + HCl(aq) ——> NaCl(aq) + H2O(l) Na + O 2- Na +

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES MgO • white solid • giant ionic lattice • sparingly soluble in water to form hydroxide (pH = 9) (Low solubility is due to metal’s greater charge density) MgO(s) + H2O(l) ——> Mg(OH)2(aq) • reacts with acids to form salts – A BASIC OXIDE MgO(s) + 2HCl(aq) ——> MgCl2(aq) + H2O(l) Mg 2+ O 2-

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES Al2O3 • giant lattice with some covalent character • insoluble in water • AMPHOTERIC; it reacts with both acids and alkalis to give salts with acids Al2O3(s) + 6HCl(aq) ——> 2AlCl3(aq) + 3H2O(l) with alkalis Al2O3(s) + 2NaOH(aq) + 3H2O(l) ——> 2NaAl(OH)4(aq) There is no need to learn these equations

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES SO2 • simple covalent molecule • soluble in water • reacts with water to give a weak acidic solution (pH = 3) SO2(g) + H2O(l) 2H+(aq) + SO32-(aq) O S ANGULAR / BENT There is no need to learn this equation

OXIDES OF PERIOD 3 ELEMENTS PROPERTIES SO3 • simple covalent molecule • reacts violently with water to give a strong acidic solution (pH = 0) O S TRIGONAL PLANAR