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 | |||
🔑 Pattern
Metal oxides are basic (react with acids). Non-metal oxides are acidic (react with bases / dissolve in water to form acids). Al₂O₃ is the classic amphoteric oxide – it reacts with both acids and bases.
⚠️ Examiner Trap
Students frequently call Al₂O₃ a "neutral" oxide. It is amphoteric, not neutral. Amphoteric = reacts with both acids and bases. Neutral = reacts with neither.