International General Certificate of Secondary Education (IGCSE) Chemistry Practice Exam

In an ionic lattice, what role do the ions play?

1. They act as free-moving charged particles

2. They are fixed in place within the structure

3. They share electrons freely

4. They form a simple molecular framework

The correct answer is: They are fixed in place within the structure

In an ionic lattice, the ions are indeed fixed in place within the structure, held together by strong ionic bonds between positively charged cations and negatively charged anions. This arrangement results in a repeating three-dimensional pattern, contributing to the overall stability and rigidity of the lattice. The ions cannot move freely as they do not have the ability to slide past one another due to the strong electrostatic forces of attraction that bind them in place. This structured arrangement is a key characteristic of ionic compounds, which contrasts with substances like metals where ions are free to move, or covalent compounds where atoms share electrons rather than forming distinct charged units. In ionic lattices, the inability of ions to move freely is why ionic compounds typically have high melting and boiling points and do not conduct electricity in their solid state; however, they can conduct electricity when dissolved in water or melted as the ions then become mobile.