Atomic energy level

An atomic energy level is an allowed, quantized value of an atom’s internal energy. It arises from quantum states of the electrons and, more finely, the nucleus.

Quantum state: A quantum state is the mathematical description of a physical system’s properties and possible measurement outcomes. An energy level is an allowed energy value associated with one or more quantum states.
Atomic spectrum: An atomic spectrum is the pattern of wavelengths absorbed or emitted by atoms. Its discrete lines reveal differences between atomic energy levels.
Atom: An atom is a nucleus surrounded by electrons bound through electromagnetic interaction. Atomic energy levels describe the allowed internal energies of this system.
Molecular energy level: A molecular energy level is an allowed quantized energy of a molecule, including electronic, vibrational, and rotational contributions. Molecules add vibrational and rotational structures beyond the atomic levels considered here.
Ground state: The ground state is the lowest-energy quantum state available to a system. It is the atom’s most stable energy level under specified conditions.
Schrödinger equation: The Schrödinger equation governs how quantum states evolve and determines allowed energies in many systems. Solving it for an atom produces its allowed electronic energies.
Spectral line: A spectral line is a narrow range of wavelengths associated with a specific absorption or emission process. Each line can identify a transition between two atomic levels.
Electron: An electron is a negatively charged elementary particle with intrinsic spin. Electronic states account for most familiar atomic energy levels.
Energy band: An energy band is a range of allowed electron energies in a solid, formed from many interacting atomic states. In solids, dense interacting levels form bands rather than isolated atomic energies.
Excited state: An excited state is a quantum state with more energy than the ground state. Atoms occupy these higher levels after absorbing energy.

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