Period 3 elements

• Reaction between sodium & cold H20:

  Reacts vigorously, forming a molten ball on surface, fizzing & producing H2 gas. 2Na (s) + 2H20 (l) -> 2NaOH (aq) + H2 (g).
• Reaction between magnesium & cold H20:

  Very slowly- can't see reaction, but forms weakly alkaline solution. Mg(s) + 2H2O(l) -> Mg(OH)2(aq) + H2(g). Weakly alkaline as Mg(OH)2 not very H20 soluble, so few OH- ions produced. Mg reacts faster with steam (more energy) to form Mgo: Mg(s) + H20(g) -> Mgo(s) + H2(g)
• What colour is sodium's flame?

  Yellow
• What colour is magnesium's flame?

  Brilliant white.
• What colour is phosphorus's flame?

  Brilliant white
• What colour is sulfur's flame?

  Blue
• Order of melting points in period 3 oxides?

  Mgo > Al2O3 > SiO2 > Na2O > P4O10 > SO3
• Why do P4O10 & SO3 have low mp?

  Covalent molecules-form simple molecular structures. Molecules attracted via weak IMF (dipole-dipole & van der waals)-little energy needed to overcome.
• Why does SiO2 have higher mp than other non-metal oxides?


  Giant macromolecular structure-strong covalent bonds hold structure together- lots of energy needed to break bonds & mp is high.
• What type solutions do simple covalent oxides of phosphorous & sulfur form?

  Acidic solutions (strong & pH around 0-1). Acids dissociate in solution to form a conjugate base.
• Why is SiO2 insoluble in water?

  Giant covalent structure- can react with bases to form salts so it's classed as acidic.
• Why is Al2O3 amphoteric?

  Al2O3 (partially ionic & partially covalently bonded) insoluble in water. Reacts with acids & bases to form salts ( it can act as acid or base).
• Define amphoteric:


  Has properties of acid & base.
• Reactions between period 3 oxides & acids & bases:

  Na & Mg oxides basic, so neutralise acids. Si, P & S oxides acidic, so neutralise bases. Al oxides amphoteric, so can neutralise acids or bases.
• What happens when ionic oxides of Na & Mg dissolve in water?

  Ionic oxides of Na & Mg contain oxide ions (O2-). When they dissolve in water, O2- ions accept protons from H20 molecules to form hydroxide ions. Solutions both alkaline, but NaOH is more soluble in water, so it forms a more alkaline solution than Mg(OH)2.
• Why do Na2O, MgO & Al2O3 have high melting points?

  Form giant ionic lattices-strong forces of attraction between each ion. Lots of heat energy needed to break bonds & melt them. MgO has higher mp than Na2O as Mg forms 2+ions which attract O2- ions more strongly than na+ ions in Na2O. Al2O3 has lower mp than Mgo as difference in electronegativity between Al & O isn't as large as between Mg & O. O2- ions in Al2O3 can't attract electrons in metal-oxygen bond as strongly as in MgO-makes bonds in Al2O3 partially covalent. Mgo>Al2O3>Na2O
• Sodium + oxygen:


  2Na + 1/2 O2 -> Na2O
• Magnesium + oxygen:


  Mg + 1/2 O2 -> MgO
• Aluminium + oxygen:

  2Al + 1.5 O2 -> Al203
• Silicon + oxygen:

  Si + O2 -> SiO2
• Phosphorous + oxygen:

  P4 + 5O2 -> P4O10
• Sulfur + oxygen:

  S + O2 -> SO2
• pH of solution produced by Na2O in water?

  12-14
• pH of solution produced by mgO in water?

  9-10
• Observation when Mg reacts with steam:

  Bright light
• Which period 3 elements react vigorously in air?

  Sodium & magnesium. P spontaneously combusts & S burns steadily.
• Which period 3 elements react slowly in air?

  Aluminium & Silicon
• Phosphoric acid formation


  P4O10 + 6H20 -> 4H3PO4
• Sulfurous acid formation


  SO2 + H2O -> H2SO3
• Sulfuric acid formation


  SO3 + H20 -> H2SO4
• Al2O3 + 3H2SO4 -> Al2(SO4)3 + 3H2O
• Al2O3 + 2NaOH + 3H2O -> 2NaAl(OH)4