In the reactivity series, metals are arranged from most reactive to least reactive. The series helps predict how metals will react with acids, water, and other substances.
| Rank | Metal |
|---|---|
| 1 | Potassium (K) |
| 2 | Sodium (Na) |
| 3 | Calcium (Ca) |
| 4 | Aluminium (Al) |
| 5 | Iron (Fe) |
| 6 | Zinc (Zn) |
| 7 | Magnesium (Mg) |
| 8 | Lead (Pb) |
| 9 | Copper (Cu) |
Aluminium sits high in the series, meaning it is quite reactive. However, in everyday life it often looks like it doesn’t react at all. Why?
The answer lies in a thin, invisible oxide layer that forms instantly when aluminium is exposed to air.
When aluminium is cut or scratched, the surface reacts with oxygen:
\$2Al + 3O2 \rightarrow 2Al2O_3\$
This reaction creates a very thin film of aluminium oxide (\$Al2O3\$) that covers the metal. The film is:
Because the oxide layer is so stable, it stops further reactions from happening. It’s like a superhero’s invisible shield that protects the metal inside.
Imagine aluminium as a superhero wearing a transparent shield. The shield is so strong that it blocks any villains (reactants) from reaching the hero. Even if the hero is naturally reactive, the shield keeps them safe.
When the shield is damaged (e.g., a scratch), the hero’s skin (the metal) is exposed and can react. But the shield quickly reforms, restoring protection.
| Tip | Why It Helps |
|---|---|
| Remember the phrase “Oxide layer protects aluminium” | Quick recall for questions about reactivity. |
| Use the equation \$2Al + 3O2 \rightarrow 2Al2O_3\$ in your answer. | Shows understanding of the protective mechanism. |
| Explain that the oxide layer is thin and self‑regenerating. | Demonstrates depth of knowledge. |
| Question | Answer |
|---|---|
| Why does aluminium appear unreactive? | Because a thin, protective oxide layer (\$Al2O3\$) forms instantly, preventing further reactions. |