Period 3

• Sodium


  Reacts with cold water, fizzes around on surface
• Sodium reaction with water

  2 Na (s) + 2 H2O (l) 2 NaOH (aq) + H2 (g)
• Magnesium


  Reacts very slowly with cold water to form the hydroxide, but reacts more readily with steam to form the oxide
• Magnesium reaction with steam

  Mg (s) + H2O (g) MgO (s) + H2 (g)
• Elements that react with oxygen


  • Na
  • Mg
  • Al
  • Si
  • P
  • S
• Sodium reaction with oxygen

  4 Na (s) + O2 (g) 2 Na2O (s)
• Magnesium reaction with oxygen

  2Mg (s) + O2 (g) 2MgO (s)
• Aluminum reaction with oxygen

  4Al (s) + 3O2 (g) 2Al2O3 (s)
• Silicon reaction with oxygen


  Si (s) + O2 (g) SiO2 (s)
• Phosphorus reaction with oxygen

  4P (s) + 5O2 (g) P4O10 (s)
• Sulfur reaction with oxygen


  S (s) + O2 (g) SO2 (g)
• Ionic oxides


  • High melting points, ionic giant lattice structures, strong forces of attraction between oppositely charged ions
• Macromolecular oxides


  • Many very strong covalent bonds between atoms, high energy needed to break the bonds, very high melting and boiling points
• Simple molecular oxides


  • Weak intermolecular forces between molecules (van der Waals + permanent dipoles), lower melting points
• Proving ionic compounds contain ions

  Melt the solids and show they conduct electricity
• Aluminium metal is protected from corrosion in moist air by a thin layer of aluminium oxide
• Sodium is stored under oil and phosphorus under water to stop these elements coming into contact and reacting with air
• Reaction of basic oxides with acids


  Na2O (s) + 2 HCl (aq) 2NaCl (aq) + H2O (l)

  MgO (s) + 2 HCl (aq) MgCl2 (aq) + H2O (l)
• Ionic equation for reaction of basic oxides with acids


  Na2O (s) + 2H+ (aq) 2Na+ (aq) + H2O (l)

  MgO (s) + 2 H+ (aq) Mg2+ (aq) + H2O (l)
• Amphoteric


  Can act as both an acid and an alkali
• Aluminum oxide acting as a base

  Al2O3 (s)+ 3H2SO4 (aq) Al2(SO4)3 (aq) + 3H2O (l)

  Al2O3 + 6HCl 2AlCl3 + 3H2O
• Aluminum oxide acting as an acid

  Al2O3 (s)+ 2NaOH (aq) + 3H2O (l) 2NaAl(OH)4 (aq)

  Al2O3 (s)+ 2OH- (aq) + 3H2O (l) 2Al(OH)4- (aq)
• SiO2 has a giant covalent structure with very strong bonds, which stops it dissolving or reacting with water and weak solutions of alkali
• Reaction of SiO2 with concentrated NaOH

  2NaOH (l) + SiO2 (s) Na2SiO3 (aq) + H2O
• Reaction of acidic oxides with bases

  P4O10 (s) + 12 NaOH (aq) 4Na3PO4(aq) + 6 H2O (l)

  SO2 (g) + 2NaOH (aq) Na2SO3 (aq) + H2O (l)

  SO3 (g) + 2NaOH(aq) Na2SO4 (aq) + H2O (l)
• Ionic equations for reactions of acidic oxides with bases

  P4O10 (s) + 12 OH- (aq) 4PO4 3-(aq) + 6 H2O (l)

  SO2 (g) + 2OH- (aq) SO3 2- (aq) + H2O (l)

  SO3 (g) + 2OH- (aq) SO4 2- (aq) + H2O (l)
• pH of solutions from metal ionic oxides

  Alkaline, pH 13 for Na2O, pH 9 for MgO
• pH of solutions from non-metal covalent oxides

  Acidic, pH 0 for P4O10, pH 3 for SO2, pH 0 for SO3
• MgO is better than NaOH for treating acid in rivers and the stomach as it is only sparingly soluble and weakly alkaline so using an excess would not make the water excessively alkaline
• Equations showing formation of ions in solution

  SO2 + H2O H+ + HSO3-

  SO3 + H2O H+ + HSO4-