Molecule pieces are made up of ATOMS, which are the smallest particles of matter that can exist on their own. ATOMS are composed of protons, neutrons, and electrons, and they are the building blocks of all matter. 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 they can vary in size and shape. Molecules are essential for life, as they are responsible for the structure and function of cells, tissues, and organs.