What is a formula unit in chemistry?

In chemistry, a formula unit is the simplest ratio of ions represented in an ionic compound. It is used to describe the composition of an ionic compound in terms of the ratio of positive and negative ions present in the compound.

For example, in sodium chloride (NaCl), the formula unit is one Na+ ion for every Cl- ion, giving a ratio of 1:1. This means that the formula unit for sodium chloride is NaCl.

Formula units are used to represent the composition of ionic compounds in a way that shows the relative number of cations and anions in the compound. They do not represent individual molecules, as ionic compounds do not exist as discrete molecules. Rather, they exist as a closely packed array of cations and anions in a repeating three-dimensional lattice structure.

Formula units are important in understanding the chemical properties and behavior of ionic compounds, as well as in determining the stoichiometry of reactions involving these compounds.