A molecule member is an ATOM, which is the smallest unit of matter that can exist on its own. An ATOM is composed of a nucleus, which contains protons and neutrons, and electrons that orbit around the nucleus. Molecules are formed when two or more atoms join together, forming a chemical bond. Molecules can be made up of different types of atoms, and the number of atoms in a molecule can vary. Molecules are essential for life, as they make up the building blocks of all living things.