Description: An energy level is a discrete allowed quantum energy state within an atom or molecule. It is measured in electron volts (eV). When an electron in an atom or molecule moves from a level with higher energy to one with a lower energy this causes a photon to be emitted with an energy equal to the energy difference between the two levels. Similarly, a photon may be absorbed by an atom or molecule if its energy is the same as the energy difference between the present level and a higher level.

Related Terms:

• Atom
• Molecule
• Photon
• Electron

Term and definition status: This term and its definition have been approved by a research astronomer and a teacher

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