Question

A distinct property of ionic compounds is that they are brittle. We are taught this is due to the fact that when force is applied to the lattice, ions are shifted, resulting in positive ions repelling positive ions and negative ions repelling negative ions. As a result, the lattice shatters. Hence ionic compounds are brittle. Makes logical sense to me.

However, using similar intuition, could we not just as well take the shattered pieces and hold them together again. At some point, we should get oppositely charged ions aligning causing the shattered pieces to come together again. Obviously when we hold, table salt together, they don't come back together. So what is fundamentally wrong with my intuition here?

Answer 1

Ionic compounds are brittle due to electrostatic forces causing like-charged ions to repel when a crystal is deformed. The ions in shattered pieces cannot realign to reform the lattice without precise conditions, explaining why they don't stick back together.

Step-by-step explanation:

The brittleness of ionic compounds such as table salt (NaCl) can be explained by the electrostatic forces that hold the ions in a fixed position in the crystal lattice. When force is applied, these ions can move and cause like-charged ions to repel each other violently, leading to shattering. Although opposite charges do attract, when the crystal is shattered, the surface atoms do not easily realign to allow the crystal to stick back together. This is because the shattered pieces have irregular shapes, and the ions are not in a position to realign perfectly due to the lack of mobility of ions in the solid state. Additionally, external conditions are not conducive to the re-formation of the bonds without the precise conditions of temperature and pressure that are often required to form the crystal lattice initially.

Attempting to press the broken pieces together does not provide the necessary energy and optimal conditions needed to reform the ionic bonds over the entire cracked surface. This explanation clarifies why brittleness is a distinct property, and why shattered ionic crystals do not easily fuse back together upon the mere application of pressure.