Question

Ionic compounds are considered brittle as similarly charged ions may come together, repelling each other and shattering the lattice. So why can't ionic compounds come back together again by this same logic?

Answer 1

The brittleness of ionic compounds is indeed related to the repulsion between similarly charged ions within the lattice. When a force is applied to an ionic solid, such as through mechanical stress, the crystal lattice can become distorted. If the stress is sufficient to bring similarly charged ions closer together, the repulsive forces between them become stronger, causing the crystal lattice to break along planes of weakness.

While it may seem logical that the repulsion between similarly charged ions could push the broken pieces back together, several factors prevent this from happening:

1. Irreversible damage: When an ionic compound breaks, the crystal structure is disrupted, and the broken pieces lose their original orientation and arrangement. It is challenging for the broken fragments to realign perfectly due to the random nature of the breakage. Even if the fragments were able to come into proximity again, the chance of achieving the original lattice arrangement is extremely low.

2. High activation energy: The reformation of the crystal lattice requires overcoming a significant energy barrier to bring the ions back into their proper positions. This energy barrier, known as the activation energy, is typically quite high for ionic compounds, making it energetically unfavorable for the fragments to reassemble spontaneously.

3. Lack of mobility: Ions in an ionic solid are typically held in fixed positions within the lattice, restricting their ability to move and reposition themselves. The absence of molecular mobility inhibits the realignment of the broken pieces and the reformation of the crystal lattice.

4. Imperfections and defects: The presence of impurities, defects, or dislocations within the crystal lattice further hinders the reassembly of broken ionic compounds. These imperfections disrupt the regular arrangement of ions and create obstacles to reformation.

Overall, while the repulsion between similarly charged ions is responsible for the brittleness of ionic compounds, the complex nature of the crystal lattice and the difficulty in reversing the structural damage prevent the broken pieces from spontaneously coming back together.