1. Oxidation: Aluminum readily reacts with oxygen to form aluminum oxide (Al2O3). This process is known as oxidation and occurs when aluminum is exposed to air or water. The oxide layer protects the metal from further corrosion.

2. Reaction with Acids: Aluminum reacts with acids to produce hydrogen gas and a salt of aluminum. For example, when aluminum is placed in hydrochloric acid (HCl), it reacts to form aluminum chloride (AlCl3) and hydrogen gas (H2).

3. Reaction with Alkalis: Aluminum reacts with alkalis to form a soluble aluminate ion (AlO2-). For example, when aluminum is added to sodium hydroxide (NaOH), it reacts to form sodium aluminate (NaAlO2) and hydrogen gas (H2).

4. Combustion: When aluminum is heated in the presence of oxygen, it undergoes a highly exothermic reaction, releasing a large amount of heat and light. This process is known as combustion and results in the formation of aluminum oxide.

5. Reduction: Aluminum can be reduced from its compounds by more reactive metals, such as sodium or potassium. For example, when aluminum oxide is heated with sodium, it undergoes a reduction reaction to form aluminum metal and sodium oxide.