Atomic physics
Atomic physics studies the structure, properties, and interactions of atoms, especially the behavior of their electrons and nuclei.
Atomic structure: The arrangement of an atom’s nucleus and electrons, including their charges, masses, and spatial organization. It supplies the basic parts whose properties atomic physics describes.
Atomic spectroscopy: The study of atoms through their absorption, emission, or scattering of electromagnetic radiation. Spectral lines expose atomic energy differences and identify elements.
Atomic clock: A clock that measures time using a stable frequency associated with a transition between atomic states. Atomic transition frequencies provide reproducible standards for measuring time.
Molecular physics: The study of the structure, properties, and interactions of molecules. It shifts the focus from individual atoms to bonded groups of atoms.
Franck–Hertz experiment: A 1914 experiment showing that electrons transfer energy to mercury atoms in discrete amounts. Its results supplied early evidence for quantized atomic energy levels.
Quantum mechanics: The physical theory describing matter and energy at atomic and subatomic scales. Atomic structure and electron behavior require its rules.
Quantum transition: A change in a quantum system from one state to another, often involving energy exchange. Electron transitions produce the characteristic absorption and emission of atoms.
Laser cooling: Techniques that use light to reduce the motion and temperature of atoms. It prepares slow, well-controlled atoms for precise experiments.
Nuclear physics: The study of atomic nuclei, including their structure, reactions, and decay. It centers the nucleus, while atomic physics usually emphasizes electrons and whole-atom behavior.
Bohr model: A 1913 model of hydrogen that assigns electrons quantized orbits around the nucleus. It introduced quantized atomic states before the modern quantum-mechanical account.