Kaavayksikköjä

Kaavayksikköjä, or formula units, are the smallest electrically neutral groups of ions in an ionic compound. For ionic compounds, which are formed by electrostatic attraction between positively charged cations and negatively charged anions, it is not possible to isolate individual molecules. Instead, these compounds exist as a large, repeating three-dimensional lattice structure of ions. The formula unit represents the simplest whole-number ratio of cations to anions that balances the charges within this lattice.

For example, in sodium chloride (NaCl), the formula unit consists of one sodium ion (Na+) and one chloride ion (Cl-). This ratio indicates that for every sodium ion present in the crystal lattice, there is also a chloride ion. The empirical formula of an ionic compound is determined by its formula units. Unlike molecular compounds, where the molecular formula represents discrete molecules, the formula unit for an ionic compound represents the fundamental repeating unit within the ionic lattice. Therefore, when discussing the composition or stoichiometry of ionic compounds, it is the formula unit that is considered.