why metals are hard in nature ? why reactivity of aluminium is decreased when it exposed into air
Answers
Answer:
When Al is dipped in nitric acid a layer of aluminium oxide is formed on the metal. This happens because nitric acid is a strong oxidizing agent. The layer of aluminium oxide prevents further reaction of aluminium and due to this reactivity of Al decreases.
Answer:
Metal has lots of free electrons which create a huge electron pressure (on the order of 100,000 atm), so to crush them, pressures higher than their internal electron gas pressure is required; this is why they are hard.
Aluminium develops a thin oxide layer when exposed to air. This aluminium oxide coat makes it resistant to further corrosion. The resistance can be improved further by making the oxide layer thicker The oxygen gas evolved at the anode reacts with aluminium to make a thicker protective oxide layer.