What is the primary characteristic of molecules?

The primary characteristic of molecules is that they are the smallest unit of a substance that retains specific chemical properties. Molecules are formed when two or more atoms are chemically bonded together. This bonding results in unique chemical characteristics that are distinct from the individual atoms. For instance, a water molecule (H2O) exhibits properties such as being a liquid at room temperature, having a high specific heat, and being a solvent for many substances, which are not characteristics of the individual hydrogen and oxygen atoms on their own.

The definition provided captures the essence of molecules, highlighting that they maintain the identity and properties of the substance they form. This foundational concept is critical in chemistry, as it distinguishes molecules from atoms and explains their behavior in various chemical reactions and interactions. Understanding molecules in this context is essential for grasping more complex chemical phenomena and reactions in any study of chemistry or materials science.