2.4 Period 3 Flashcards
How does sodium react with cold water?
It fizzes and moves on the surface, forming sodium hydroxide and hydrogen:
2 Na (s) + 2 H₂O (l) → 2 NaOH (aq) + H₂ (g)
How does magnesium react with water and steam?
Slowly with cold water to form Mg(OH)₂; reacts more readily with steam to form MgO and H₂:
Mg (s) + H₂O (g) → MgO (s) + H₂ (g)
What kind of bonding do Na₂O, MgO, Al₂O₃ have?
Ionic bonding with high melting points due to strong electrostatic forces in a giant lattice.
Why does Al₂O₃ show some covalent character?
Due to small Al³⁺ ion polarizing the O²⁻ cloud; lower electronegativity difference.
What is the structure of SiO₂?
Macromolecular with strong covalent bonds; very high melting and boiling point.
Why do P₄O₁₀ and SO₂ have low melting points?
They are simple covalent molecules with weak intermolecular forces.
What do basic oxides like Na₂O and MgO form when they react with acids?
They form salts and water:
Na₂O + 2 HCl → 2 NaCl + H₂O
MgO + 2 HCl → MgCl₂ + H₂O
Why is Al₂O₃ amphoteric?
It reacts with both acids and bases.
Acid: Al₂O₃ + 6 HCl → 2 AlCl₃ + 3 H₂O
Base: Al₂O₃ + 2 NaOH + 3 H₂O → 2 NaAl(OH)₄
How does SiO₂ behave in acid-base reactions?
Does not react with water or weak alkali; reacts with hot conc. NaOH:
2 NaOH + SiO₂ → Na₂SiO₃ + H₂O
Which Period 3 oxides are soluble and form alkaline solutions?
Na₂O + H₂O → 2 Na⁺ + 2 OH⁻ (pH ≈ 13)
MgO + H₂O → Mg(OH)₂ (pH ≈ 9, limited solubility)
Which oxides are insoluble in water?
Al₂O₃ and SiO₂ — no reaction with water, neutral pH (≈7).
What acids form from P₄O₁₀, SO₂, and SO₃ in water?
P₄O₁₀ + 6 H₂O → 4 H₃PO₄ (pH ≈ 0)
SO₂ + H₂O → H₂SO₃ (pH ≈ 3)
SO₃ + H₂O → H₂SO₄ (pH ≈ 0)
