An atom is the smallest particle of an element that can exist and still retain the properties of that element. Atoms are made up of protons, neutrons, and electrons, and they are the building blocks of all matter. Atoms are held together by chemical bonds, which allow them to form molecules and other compounds. Atom and Molecule define the two most basic units of a substance. An atom is the smallest unit of matter that can exist by itself and still retain the properties of the element it belongs to. A molecule is two or more atoms bonded together to form a single, more complex unit. A molecule can be composed of different elements or the same element bonded together. In chemistry, a molecule is two or more atoms that are bound together by covalent bonds. Molecules can be single atoms, like oxygen (O2), or very complex, like proteins. In general, molecules are the smallest unit of a substance that can exist independently and still retain the properties of that substance.
