Period 3 & Oxides

• Physical properties of period 3:

  • Atomic radius - decreases
  • Electronegativity - increases
  • First ionisation energy - increases
• Atomic radius - decreases:

  • Increase in nuclear charge
  • Same amount of shielding
  • Electrons shells held closer to the nucleus
• Electronegativity - increases:

  • Increase in nuclear charge
  • Same amount of shielding
  • Increasing capability of withdrawing electron density from a covalent bond
• Ionisation energy - increases:

  • Increased nuclear charge
  • Same amount of shielding
  • Stronger attraction between nucleus and outer electron
• Silicon has highest melting point:

  • Macromolecular structure
  • Lots of covalent bonds
  • Strong covalent bonds require lots of energy to overcome
• Non-metals (P4, S8, Cl2):

  • Simple molecules with van der waals between molecules
  • Strength of van der waals depends on the size of the molecule
  • Argon exists as single atoms with the weakest van der waals
• Aluminium has the highest boiling point:

  • Liquid state aluminium still has strong electrostatic attraction between ions and delocalised electrons
  • Large amount of energy needed to boil
• Period 3 elements + water:

  2Na + 2H2O -> 2NaOH + H2 (pH 13-14)

  Mg + 2H2O -> Mg(OH)2 + H2 (pH 9-10)

  Mg + H2O -> MgO + H2 (steam)

  Cl2 + H2O -> HClO + HCl (pH 2-3)

  2Cl2 + 2H2O -> 4HCl + O2 (pH 2-3)
• Sodium + water:

  Obs: Metal fizzes rapidly and melts due to heat produced
• Magnesium + water:

  Obs: Few bubbles after a few days, very slow rate of reaction
• Magnesium + steam:

  Obs: Faster due to higher temperatures
• Period 3 elements + oxygen:

  2Na + 0.5O2 -> Na2O

  2Mg + O2 -> 2MgO

  4Al + 3O2 -> 2Al2O3 (pH 7)

  Si + O2 -> SiO2 (pH 7)

  P4 + 5O2 -> P4O10

  S + O2 -> SO2
• Sodium + oxygen:

  Obs: Yellow flame -> white solid
• Magnesium + oxygen:

  Obs: White flame -> white solid
• Aluminium + oxygen:

  Obs: White flame -> Al2O3
• Red phosphorus is made of chains of P4 tetrahedrons
• Phosphorus + oxygen:

  Red allotrope needs heat to react

  White allotrope reacts rapidly with air

  Obs: White flame -> White fumes
• Sulfur + oxygen:

  Obs: Pale blue flame -> Colourless gas
• Compounds with ionic bonds + giant ionic structure:

  • Na2O
  • MgO
  • Al2O3
• Compounds with covalent bonds + structure:

  • SiO2 (macromolecule)
  • P4O10 (simple molecule)
  • SO3 (simple molecule)
  • SO2 (simple molecule)
• Period 3 oxides + water:

  Na2O + H2O -> 2Na+ + 2OH- (pH 13-14)

  MgO + H2O -> Mg(OH)2 (pH 9-10)
• Aluminium oxide and silicon dioxide are insoluble so when water added pH remains 7
• Explain why sodium oxide forms an alkaline solution with water:

  • O2- ions in sodium oxide react with water forming OH-
  • O2- + H2O -> 2OH-
• Acidic oxides:

  P4O10 + 6H2O -> 4H3PO4 (pH 1-2)

  SO2 + H2O -> H2SO3 (pH 2-3)

  SO3 + H2O -> H2SO4 (pH 0-1)
• Basic oxides:

  Na2O + H2SO4 -> Na2SO4 + H2O

  MgO + 2HCl -> MgCl2 + H2O
• Amphoteric oxides:

  Al2O3 + 6HCl -> 2AlCl3 + 3H2O

  Al2O3 + 2NaOH + 3H2O -> 2NaAl(OH)4
• Acidic oxides:

  H3PO4 + 3NaOH -> Na3PO4 + 3H2O

  P4O10 + 12NaOH -> 4Na3PO4 + 6H2O

  SO2 + 2NaOH -> Na2SO3 + H2O
• Acid-base reactions:

  P4O10 + 6Na2O -> 4Na3PO4

  P4O10 + 6MgO -> 2Mg3(PO4)2
• Why silicon oxide is classed as an acidic oxide:

  • SiO2 neutralises bases
  • SiO2 + 2NaOH -> Na2SiO3 + H2O
• Mg(OH)2 is sparingly soluble
• Ion equation:

  SO2 + H2O -> H+ + HSO3-
• Amphoteric ionic equations:

  Al2O3 + 6H+ -> 2Al3+ + 3H2O

  Al2O3 + 2OH- + 3H2O -> 2Al(OH)4-
• How to find melting point of ionic compound:

  • Melt it
  • Conducts electricity in molten state
• How to find purity of P4O10:

  • Capillary in oil tube
  • Heat slowly
  • Range of melting points shows impure compound
• Al2O3 is insoluble in water
• Test between SO2 and SO3:

  • Universal indicator
  • SO2 - Orange-red
  • SO3 - Red
• Why silicon dioxide is insoluble in water:

  • Macromolecule
  • Strong covalent bonds between atoms
  • Water cannot break the covalent bonds