energy level

A Dictionary of Astronomy | 1997 | 700+ words | Copyright

energy level The discrete energy state of an electron in an atom or molecule. Electrons can occupy only specific energy levels and jump from one energy level to another. The lowest energy level is called the ground state of the atom or molecule. Within an atom, energy levels correspond to the distance from the nucleus. The electron requires energy to jump from a state of lower energy (an energy level close to the nucleus) to a higher energy level (further from the nucleus); the atom is then said to be excited. Energy levels are defined by a quantum number, symbol n. For the ground state, n = 1. Higher energy levels are numbered 2, 3, etc., outwards from the nucleus. When an electron jumps from a higher energy level to a lower energy level it emits a photon, the energy of which is equal to the difference between the two energy levels.

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