Aluminium (Al) — Atomic Number 13

Aluminium is a chemical element with the symbol Al and atomic number 13. It is a silvery-white, lightweight metal — the most abundant metal in Earth’s crust (~8%). The Hall-Héroult process (1886) made it cheap and widely available.

At a Glance

Chemical Properties

Aluminium is reactive but protected by a thin, tough layer of aluminium oxide (Al₂O₃) that forms instantly in air. This makes it appear unreactive. Aluminium is amphoteric — it reacts with both acids and alkalis.

Key Reactions

1. With acid: $2\text{Al}+6\text{HCl}\to 2{\text{AlCl}}_3+3{\text{H}}_2$
2. With alkali: $2\text{Al}+2\text{NaOH}+2{\text{H}}_2\text{O}\to 2{\text{NaAlO}}_2+3{\text{H}}_2$
3. Thermite reaction: $2\text{Al}+{\text{Fe}}_2{\text{O}}_3\to 2\text{Fe}+{\text{Al}}_2{\text{O}}_3$ (used to weld railway lines)

Extraction — Hall-Héroult Process

1. Bauxite (Al₂O₃) is purified
2. Dissolved in molten cryolite (Na₃AlF₆) — lowers melting point from ~2000 °C to ~950 °C
3. Electrolysis: Al³⁺ + 3e⁻ → Al at cathode
4. Very energy-intensive — recycling uses only 5% of the energy

Uses

• Aircraft, cars, drink cans, kitchen foil
• Overhead power cables — lightweight, good conductor
• Window frames — does not rust (oxide layer protects)

IGCSE Essentials

1. Amphoteric — reacts with both acids AND alkalis
2. Protected by oxide layer (Al₂O₃)
3. Extracted from bauxite by electrolysis in molten cryolite
4. Forms Al³⁺ (loses 3 electrons)
5. Recycling saves 95% energy

Sources

• Aluminium — Wikipedia
• Aluminium — Ptable.com