Energy Levels
Definition and meaning of Energy Levels in chemistry.
Energy levels (also called electron shells) are the discrete, quantized distances from an atom's nucleus at which its electrons are allowed to exist, each corresponding to a fixed amount of energy. Electrons cannot occupy the space between levels; they exist only in these specific, allowed states.
In more detail
Each energy level is identified by a principal quantum number, n = 1, 2, 3…, and is traditionally labeled K, L, M, N and so on outward from the nucleus. Levels closer to the nucleus (lower n) have lower energy and hold fewer electrons; a shell's maximum capacity is given by 2n². Each shell also contains one or more subshells (s, p, d, f), which are further divided into orbitals. Electrons can move between levels only by absorbing or emitting a photon whose energy exactly equals the gap between the two levels, which is the origin of atomic emission and absorption spectra.
Key facts
| Field | General Chemistry |
|---|---|
| Also called | Electron shells, shells |
| Max electrons per shell | 2n² (n = principal quantum number) |
| Shell labels | K (n=1), L (n=2), M (n=3), N (n=4)… |
Sodium (electron configuration 2, 8, 1) has three occupied energy levels: the first (K, n=1) holds 2 electrons, the second (L, n=2) holds 8, and the third (M, n=3) holds a single valence electron, which sodium readily loses to form Na⁺.
Frequently asked questions
What's the difference between an energy level and an orbital?
An energy level (shell) is the set of all electrons sharing the same principal quantum number n; an orbital is a specific region within a subshell of that level where an electron is likely to be found.
Why do electrons jump between energy levels?
An electron moves to a higher level by absorbing a photon of exactly matching energy, and drops to a lower level by emitting one, producing the characteristic line spectra of each element.