Metallic character decreases across a period (left → right) and increases down a group. This mirrors the trends in ionisation energy - metals lose electrons easily.
Oxide Acid-Base Character Across Period 3
| Oxide | Na₂O | MgO | Al₂O₃ | SiO₂ | P₄O₁₀ | SO₃ | Cl₂O₇ |
|---|---|---|---|---|---|---|---|
| Character | Basic | Basic | Amphoteric | Weakly acidic | Acidic | Strongly acidic | Strongly acidic |
| Bonding | Giant ionic | Ionic/covalent | Giant covalent | Simple molecular | |||
Oxide Trend
Acid-Base Nature of Period 3 Oxides
Metal oxides (Na2O, MgO) are basic (react with acids to form salts). Non-metal oxides (P4O10, SO3, Cl2O7) are acidic (react with bases and form acids in water). Al2O3 is amphoteric (reacts with both acids and bases).
Examiner Trap
Al2O3 Is Amphoteric, Not Neutral
Students frequently call Al2O3 a "neutral" oxide. It is amphoteric, not neutral. Amphoteric means it reacts with both acids and bases. Neutral oxides (like CO or NO) react with neither.
AQA GCSE & IB Chemistry
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