In chemistry, what is a molecule defined as?

A molecule is defined as the smallest unit of a compound that retains the chemical properties of that compound. This means that a molecule is composed of two or more atoms that are bonded together chemically. For instance, water (H₂O) is a molecule made up of two hydrogen atoms and one oxygen atom. When discussing compounds, it is essential to understand that molecules represent the simplest form of that compound—if you were to break it down further, you would no longer have that substance, as the distinct properties are tied to the specific arrangement and types of atoms involved in the bonding.

In contrast, a single atom of an element refers to the basic building block of that element, but on its own, it does not represent a compound. A general term for all physical matter encompasses everything from atoms to large structures but does not define what a molecule is specifically. Similarly, a collection of protons and neutrons describes particles found in the nucleus of an atom and does not address the concept of molecular structure or the combination of atoms to form compounds.