9701 · 9.2
Periodicity of chemical properties of the elements in Period 3
As we move across Period 3, the character of the elements' oxides changes dramatically from strongly basic to strongly acidic. This trend is mirrored by their chlorides, which hydrolyse to produce solutions of varying pH.
Need to know
What you need to know
- Sodium: 2Na(s) + ½O₂(g) → Na₂O(s)
- Magnesium: 2Mg(s) + O₂(g) → 2MgO(s)
- Aluminium: 4Al(s) + 3O₂(g) → 2Al₂O₃(s)
- Silicon: Si(s) + O₂(g) → SiO₂(s)
- Phosphorus: P₄(s) + 5O₂(g) → P₄O₁₀(s)
- Sulfur: S(s) + O₂(g) → SO₂(g) (can be further oxidised to SO₃)
Explanation
Period 3: From Base to Acid
- Na₂O, MgO basic; Al₂O₃ amphoteric; SiO₂, P₄O₁₀, SO₃ acidic oxides.
- Reaction with water: Na vigorous; Mg slow; Al/Si insoluble oxides.
- Chlorides: NaCl neutral; AlCl₃, SiCl₄ hydrolyse to acidic solutions.
- Max oxidation state rises to Group 15 then falls — inert pair effect later.