Final answer:
The three-dimensional arrangement of ions in ionic compounds is known as a crystal lattice, which maximizes attractive forces and stability.
Step-by-step explanation:
The rigid three-dimensional arrangement assumed by the ions of ionic compounds is called a crystal lattice. Ionic compounds do not exist as discrete molecules; instead, to minimize the potential energy of the system, they form an extended array of alternating cations and anions. These ions are positioned to maximize the attractive forces between the oppositely charged particles in a crystal lattice. This structure is more stable than separate pairs of ions, as each ion in the lattice is surrounded by multiple counterions, enhancing ionic interactions.