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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.