Complete the following sentence: Substances within a homologous series have the same ______ ; Your answer here;group.

Substances within a homologous series have the same functional group.

A homologous series is a group of organic compounds that share a similar structure and exhibit a gradual trend in physical properties, such as boiling point and solubility. The distinguishing feature of these compounds is that they have the same functional group, which is the specific arrangement of atoms that imparts characteristic properties and reactivity to the molecules. For instance, alcohols form a homologous series, with all members containing the hydroxyl (-OH) functional group. This commonality leads to similar chemical behaviors, making it easier to predict how different compounds within the series will react under various conditions. Understanding these relationships aids chemists in synthesizing compounds and predicting their behavior in chemical reactions.