Stories We Like: A Guide to the Comma
The simplest modern picture of the structure of the atom, according to which electrons move in orbits around the nucleus. The electron's orbits can exist only at certain well-defined distances from the nucleus. When an electron changes orbits, it does so in a sudden quantum leap. The energy difference between the initial and final orbit is emitted by the atom in bundles of electromagnetic radiation called photons.
Note: The Bohr atom is named after the twentieth-century Danish physicist Niels Bohr.