Final answer:
Ionic compounds are not represented by molecular formulas because they consist of extended networks of ions, not discrete molecules, and the formula used is an empirical formula showing the ratio of ions.
Step-by-step explanation:
An ionic compound is not represented by a molecular formula because it lacks molecules in the sense of discrete, bounded units. Instead, ionic compounds consist of a crystal lattice structure comprising an extensive network of ions. These compounds contain both positive and negative ions that are electrostatically bound together, not by covalent molecular bonds, and exist as an extended array, not individual molecules.
When we write the formula for an ionic compound, such as sodium chloride (NaCl), we use an empirical formula that shows the simplest whole-number ratio of ions within the compound. This formula represents an exhaustive network of ions, rather than a single molecule, with the total number of positive and negative charges being equal, creating an electrically neutral compound. Ionic compounds, therefore, are described by their empirical formulas rather than molecular formulas.