Atom the nucleus defines to what chemical element the atom belongs: for example, all copper atoms contain 29 protons. The number of neutrons defines the isotope of the element. The number of electrons influences the magnetic properties of an atom. Atoms can attach to one or more other atoms by chemical bonds to form chemical compounds such as molecules. The ability of atoms to associate and dissociate is responsible for most of the physical changes observed in nature and is the subject of the discipline of chemistry. The idea that matter is made up of discrete units is a very old
Atom laser an optical and an atom laser are that atoms interact with themselves, cannot be created as photons can, and possess mass whereas photons do not (atoms therefore propagate at a speed below that of light). The van der Waals interaction of atoms with surfaces makes it difficult to make the atomic mirrors, typical for conventional lasers. A pseudo-continuously operating atom laser was demonstrated for the first time by Theodor Hänsch, Immanuel Bloch and Tilman Esslinger at the Max Planck Institute for Quantum Optics in Munich. They produce a well controlled continuous beam spanning up to 100 ms, whereas their predecessor