What is a molecule?

A molecule is defined as a group of atoms that are bonded together, forming the smallest unit of a chemical compound that retains the compound's chemical properties. This definition emphasizes the fact that molecules are made up of multiple atoms, which can be the same or different elements, that are held together by chemical bonds such as covalent bonds.

For example, water (H2O) is a molecule comprised of two hydrogen atoms and one oxygen atom bonded together. This molecular structure gives water its unique properties, which are critical for its role in chemistry and biology. Understanding that a molecule is the fundamental building block of chemical compounds helps to clarify the distinctions between different forms of matter, such as single atoms or ionic collections, which do not encompass the concept of a molecule precisely as defined.