S2.1.3 Lattice structures and properties Notes

Lattice Structure and Properties of Ionic Compounds

1. When you sprinkle salt on your food, have you ever wondered why it forms tiny crystals instead of just being a shapeless powder?
2. These crystals are not random as they reflect the underlying structure of ionic compounds.

Ionic Compounds and Their Lattice Structure

These ions are not scattered randomly; instead, they form a three-dimensional lattice structure.

What is a Lattice Structure?

1. The lattice structure gives ionic compounds their characteristic properties, such as high melting points and brittleness.
2. The formula of an ionic compound, such as NaCl, represents the simplest ratio of ions in the lattice (1:1 for $Na^+$ and $Cl^-$).

Physical Properties of Ionic Compounds

Ionic compounds are known for their unique set of physical properties.

Volatility: Why Don’t Ionic Compounds Vaporize Easily?

1. Volatility refers to a substance’s ability to vaporize.
2. Ionic compounds have low volatility because their lattice structure is held together by strong electrostatic forces.
3. To break these bonds and convert the solid into a gas, a significant amount of energy is required.
4. This is why ionic compounds tend to have high melting and boiling points.

Electrical Conductivity: When Do Ionic Compounds Conduct Electricity?

To conduct electricity, a substance must have mobile charged particles. In ionic compounds:

1. In the solid state: Ions are fixed in place within the lattice and cannot move, so the compound does not conduct electricity.
2. In the molten (liquid) state or when dissolved in water (aqueous state): The lattice breaks down, freeing the ions to move and carry an electrical current.