Period 3 Oxides Flashcards

Active recall practice for Period 3 oxides, their structures, melting points, water reactions, and acid-base reactions.

Structure & Bonding: read all 5 questions and answers

Write the formulas of the Period 3 oxides studied at A-Level, distinguishing oxidation states.
Na₂O (+1), MgO (+2), Al₂O₃ (+3), SiO₂ (+4), P₄O₁₀ (+5, highest oxidation state vs P₄O₆ +3), SO₂ (+4), and SO₃ (+6, highest oxidation state for sulfur).
What is the bonding and structure of Na2O, MgO, and Al2O3?
Ionic bonding with a giant ionic crystal lattice structure.
Describe the bonding and structure of Silicon Dioxide (SiO2).
Covalent bonding with a giant covalent (macromolecular) structure.
Describe the bonding and structure of Phosphorus(V) Oxide (P4O10) and Sulfur Dioxide (SO2).
Covalent bonding with a simple molecular structure.
Why does Aluminium Oxide (Al2O3) show some covalent character?
The Al³⁺ ion is small and highly charged, giving it a high charge density that polarises the oxide (O²⁻) electron cloud.

Melting Points: read all 5 questions and answers

Why does MgO have a higher melting point than Na2O?
Mg²⁺ has a higher charge and smaller radius than Na⁺, leading to stronger electrostatic attraction between the ions in the giant lattice.
Why does Silicon Dioxide have a very high melting point?
A large amount of energy is required to break the many strong covalent bonds in its giant molecular structure.
Compare the melting points of P4O10 and SO3 and explain the difference.
P₄O₁₀ has a higher melting point because it is a larger molecule with more electrons, resulting in stronger van der Waals forces.
Why are the melting points of phosphorus and sulfur oxides much lower than those of sodium and magnesium oxides?
Phosphorus and sulfur oxides are simple molecular, requiring only weak intermolecular van der Waals forces to be overcome, not ionic or covalent bonds.
Which Period 3 element oxide has the highest melting point?
Magnesium Oxide (MgO).

Reactions with Water & pH: read all 5 questions and answers

Write the equation for the reaction of Sodium Oxide with water, and state the pH of the resulting solution.
Na₂O(s) + H₂O(l) → 2NaOH(aq); pH is 13 to 14.
Why is the pH of Magnesium Oxide in water lower than that of Sodium Oxide?
Magnesium Oxide is only sparingly soluble in water, so it produces fewer hydroxide ions (pH 9 to 10).
Why do Al2O3 and SiO2 not react with water, and what is the pH of their mixtures?
They are completely insoluble in water due to their strong ionic/covalent lattices; the pH of the mixture is 7.
Write the equation for the reaction of Phosphorus(V) Oxide with water, and state the pH of the resulting solution.
P₄O₁₀(s) + 6H₂O(l) → 4H₃PO₄(aq); pH is 1 to 2.
Write the equation for the reaction of Sulfur Dioxide with water, and identify the acid formed.
SO₂(g) + H₂O(l) → H₂SO₃(aq); the acid formed is sulfurous acid (sulfuric(IV) acid).

Acid-Base Reactions: read all 5 questions and answers

What is meant by the term amphoteric, and which Period 3 oxide is amphoteric?
Amphoteric means reacting with both acids and bases; Aluminium Oxide (Al2O3) is amphoteric.
Write the equation for the reaction of Aluminium Oxide with hydrochloric acid, including state symbols.
Al₂O₃(s) + 6HCl(aq) → 2AlCl₃(aq) + 3H₂O(l).
Write the equation for the reaction of Aluminium Oxide with hot, concentrated aqueous sodium hydroxide, including state symbols.
Al₂O₃(s) + 2NaOH(aq) + 3H₂O(l) → 2NaAl(OH)₄(aq).
Write the equation for the reaction of Sulfur Trioxide with sodium hydroxide, including state symbols.
SO₃(g) + 2NaOH(aq) → Na₂SO₄(aq) + H₂O(l).
Write the equation for the reaction of Silicon Dioxide with hot, concentrated sodium hydroxide, including state symbols.
SiO₂(s) + 2NaOH(aq) → Na₂SiO₃(aq) + H₂O(l).