What is a molecule?

A molecule is a group of two or more atoms that are chemically bonded together. It is the smallest unit of a chemical compound that retains the chemical properties of that compound. Molecules can be made up of atoms of the same element (such as O2 for oxygen) or different elements (such as H2O for water).

A molecule is the smallest unit of a chemical compound that can exist independently. It is composed of atoms that are held together by chemical bonds. Molecules can be simple, such as those composed of two atoms (e.g., H2), or complex, such as those composed of thousands of atoms (e.g., DNA). Molecules are the building blocks of all matter, and they determine the physical and chemical properties of substances.