Period 3

• elements that react with water in period 3 are: Na, Mg and Cl
• Na reacts violently with water to form sodium hydroxide (NaOH) and hydrogen gas (H2) and produces a pH of 12-14
• complete and balance the reaction of sodium in water

  2 Na + 2 H2O -> 2NaOH + H2
• Magnesium hydroxide forms a much less alkaline solution because it has a much lower solubility than sodium hydroxide.
• Complete the reaction between Aluminium an oxygen

  note that this reaction requires heat to occur

  2 Al + 3/2 O2 -> Al2O3
• The equation for this reaction is: 2Mg(s) + O2(g) → 2MgO(s)
• Aluminium oxide is amphoteric which means it can act as both acid or base depending on what it's mixed with
• Complete the reaction between silicon and oxygen

  note that this reaction requires heat to occur

  Si + O2 -> SiO2
• It would be dangerous to add sodium to a small volume of water as the mixture would explode
• In terms of bonding and structure of the period 3 oxides:

  Na2O - ionic - Giant ionic

  MgO - Ionic - Giant ionic

  Al2O3 - Ionic - Giant ionic

  SiO2 - Covalent - Giant covalent

  P4O10 - Covalent - simple covalent

  SO2 - covalent - simple covalent

  SO3- covalent - simple covalent
• period 3 oxides react with water to form acids or bases
• The period 3 oxides pH in solution decrease along the period
• The ph of NaOH is 12-14
• The pH of MgOH is 9 to 10
• The period 3 oxides that do not react with water are:(molecular formula)

  (1)Al2O3

  (2)SiO2

  Because

  (1)the oxide ions are held too strongly together in the ionic lattice

  (2)the covalent bonds are too strong to be broken by water
• List all the period 3 oxides and the pH they produce in solution:

  Na2O - 12 to 14

  MgO - 9 to 10

  Al2O3 - insoluble

  SiO2 - insoluble

  P4O10 - 1 to 2

  SO2 - 2 to 3

  SO3 - 0 to 1
• List observations and products when Na and Mg react with oxygen

  A) Na2O

  B) MgO

  C) White flame

  D) yellow flame

  E) white

  F) white

  
• Oxides that reaction with acids or bases

  Acids:

  Na2O

  MgO

  Bases:

  P4O10

  SO2

  SO3
• melting point increases across period 3 oxides from

  Na to Mg

  but then drops at Al as there is covalent character preventing electrons from feeling moving about which weakens the structure

  then sharply rises at SiO2 due to the purely covalent bonding due to its nature of being a giant covalent structure

  then sharply falls as SO2 and SO3 are simple covalent molecules with only Van der waal forces
• Al2O3 + 2NaOH → 2NaAlO2 + H2O
• SiO2  +  2NaOH  -> Na2SiO3  +  H2O
• why do Na and Mg oxides form alkaline solution in water?

  Oxide ions react with water to form hydroxide ions
• Why is NaOH more alkaline than Mg(OH)2?

  NaOH is more soluble in water
• 12NaOH + P4O10 -> 4H3PO4 + 6Na2O