Period 3

Trends:

• as you move along the period the ionisation energy increases until a new energy level is reached

  • sodium requires less energy to ionise than magnesium as magnesium has to lose two electrons to form a full outer shell (Mg²⁺) and has more protons in its nucleus

  • 2Na + 2H₂O → 2NaOH + H₂ is faster than

  • Mg(s) + 2H₂O(l) → Mg(OH)₂(aq) + H₂(g) where bubbles form slowly on the surface

  • but Mg(s) + H₂O(g - steam) → MgO(s) + H₂(g) happens quickly with bright white flame to form a white solid

Oxides:

• form oxides in their highest oxidation state (same as their group number)

  • Al → 3+ therefore Al₂O₃

  • P → 5+ therefore P₄O₁₀ NOT P₂O₅

  • sulphur can form either SO₂ (sulphur dioxide) or SO₃(sulphur trioxide) but SO₃ requires a catalyst + higher temperature

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• all the ionic oxides dissolve in water to form alkaline solutions

  • Na₂O + H₂O → 2NaOH

  • MgO + H₂O → Mg(OH)₂

• simple covalents dissolve to form acidic solutions

  • P₄O₁₀ + 6H₂O → 4H₃PO₄ (phosphoric acid)

  • SO₂ + H₂O → H₂SO₃ (sulfurous acid)

  • SO₃ + H₂O → H₂SO₄ (sulfuric acid)

When ionic oxides are mixed with an acid, neutralisation occurs

• forms a salt + water

  

• Aluminium oxide is partially covalent + ionic and so it is insoluble in water

• therefore acts as both acid and a base - it is amphoteric