Final answer:
In an ionic compound, ions are organized into a crystal lattice. This structure allows ionic crystals to be hard, brittle, and have high melting points, and they conduct electricity when molten or dissolved in solution. Polyatomic ions also contribute to the structure of ionic compounds within the lattice.
Step-by-step explanation:
The ions in an ionic compound are organized into a crystal. An ionic crystal structure is characterized by a repeating pattern of positively-charged cations and negatively-charged anions, which can be either monatomic or polyatomic. The ionic crystals' structure is commonly found in compounds formed from metals in Group 1 or 2 and nonmetals in Group 16 or 17, or from nonmetallic polyatomic ions. These ionic crystals are known for being hard, brittle, and having high melting points. Moreover, while solid ionic compounds do not conduct electricity, they do become conductive when melted or dissolved in water, due to the free movement of ions.
Polyatomic ions are a type of ions that consist of a group of atoms covalently bonded together with an overall electric charge. These ions act as a single unit, contributing to the structure of ionic compounds. Ionic substances typically form a crystal lattice, which is a regular, geometric structure with a balanced ratio of the different ions comprising the compound, such as NaCl, which has a 1:1 ratio of sodium to chloride ions.