Molecular units refer to the smallest identifiable units of a substance that retain its chemical properties. These units can be individual molecules, which are formed when two or more atoms bond together. For example, a water molecule, represented as H2O, consists of two hydrogen atoms and one oxygen atom. In chemistry, molecular units are crucial for understanding how substances interact and react with one another. They help in determining the properties of compounds, such as salts, acids, and bases. By studying these units, scientists can predict behaviors in various chemical reactions and applications.