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)
• Aluminium 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)
• You should be able to write these equations
• Learn the formulae of the oxides
• Ionic oxides


  • High melting points, ionic giant lattice structures, strong forces of attraction between oppositely charged ions
  • Increased charge on the cation makes the ionic forces stronger going from Na to Al, leading to increasing melting points
  • Al2O3 is ionic but shows some covalent character
• Macromolecular oxides


  • SiO2 has many very strong covalent bonds between atoms, high energy needed to break the bonds - very high melting and boiling points
• Simple molecular oxides


  • P4O10 (s), SO2 (g) have weak intermolecular forces between molecules (van der waals + permanent dipoles), so have lower melting points
  • P4O10 has larger van der waals forces and higher melting point than SO2
• To prove the 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


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

  2. Na2O (s) + H2SO4 (aq) Na2SO4 (aq) + H2O (l)

  3. MgO (s) + 2 HCl (aq) MgCl2 (aq) + H2O (l)
• Ionic equations for basic oxide reactions with acids


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

  2. MgO (s) + 2 H+ (aq) Mg2+ (aq) + H2O (l)
• Most acid-base reactions follow the pattern: acid + base salt + water
• Know the charges on the ions e.g. PO4^3-, SO4^2-
• Amphoteric oxides


  Aluminium oxide can act as both an acid and an alkali
• Aluminium oxide acting as a base


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

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


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

  2. Al2O3 (s)+ 2OH- (aq) + 3H2O (l) 2Al(OH)4- (aq)
• SiO2


  Has a giant covalent structure with very strong bonds, stops it dissolving or reacting with water and weak solutions of alkali, but will react with very concentrated NaOH
• Reaction of acidic oxides with bases

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

  2. P4O10 + 6 Na2O 4Na3PO4

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

  4. SO3 (g) + 2NaOH(aq) Na2SO4 (aq) + H2O (l)
• Ionic equations for acidic oxide reactions with bases

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

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

  3. SO3 (g) + 2OH- (aq) SO4^2- (aq) + H2O (l)
• Be careful for whether the question is asking for an ionic equation or a full one
• Trend in reactions of oxides with water


  • Metal ionic oxides tend to react with water to form hydroxides which are alkaline
  • Non-metal, simple molecular, covalent, oxides react with water to give acids
  • Aluminium oxide is amphoteric, can act as both a base and an acid
• Reaction of metal oxides with water


  1. Na2O (s) + H2O (l) 2Na+ (aq) + 2OH- (aq) pH 13

  2. MgO (s) + H2O (l) Mg(OH)2 (s) pH 9
• Al2O3 and SiO2 do not dissolve in water
• Reaction of non-metal oxides with water


  1. P4O10 (s) + 6 H2O (l) 4 H3PO4(aq) pH 0

  2. SO2 (g) + H2O (l) H2SO3 (aq) pH 3

  3. SO3 (g) + H2O (l) H2SO4 (aq) pH 0
• 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-
• Displayed formulae of acids: H2SO4, H2SO3, H3PO4