Final answer:
Ions in crystals form a repeating pattern or lattice, where cations and anions alternate to maximize electrostatic attraction, leading to the unique physical properties of ionic compounds.
Step-by-step explanation:
The arrangements of ions in crystals is a fundamental concept in chemistry. Ions in crystals do not occupy random or isolated positions, nor are they arranged by atomic number. Instead, ions arrange themselves in a repeating pattern or lattice. This lattice structure is a highly organized, three-dimensional array of alternating positively-charged cations and negatively-charged anions. The specific arrangement allows for the maximization of electrostatic attraction, which results in the formation of crystalline structures that are typically hard, brittle, and have high melting points. These ionic compounds conduct electricity when molten or in aqueous solution, owing to the free movement of ions, but not as solids due to the fixed positions of ions in the lattice.Different sized ions pack together to form complex crystalline structures. For example, small cations tend to occupy tetrahedral spaces within a close-packed array of anions, while larger cations fit into octahedral or cubic holes depending on their size. The precise structure of these ionic crystals can be analyzed and determined using techniques such as X-ray diffraction.