What is the difference between electron shells and electron orbitals?
1 Answer
The dimensionality...?
- The term "electron shells" originates from the Bohr model, a two-dimensional model based on the hydrogen atom only.
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It assumes fixed orbits (positions) and fixed trajectories (momenta), and such simultaneous known quantities disobeys the Heisenberg Uncertainty Principle. It also does not identify quantum numbers
#n# ,#l# ,#m_l# , or#m_s# .
- The term "electron orbitals" is part of the modern quantum theory, and is based on a three-dimensional model for any atom.
Such orbitals are regions of electron density, and are related to the probability densities of electron position over allspace, averaged over infinite time.
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The term "electron shell" lingers on through quantum theory with multi-electron atoms, labeling "shells" as corresponding to each principal quantum number
#n# and "subshells" as corresponding to each angular momentum quantum number#l# .(Electron energy levels do not exist unless the quantum state is accessed, but we still like to think of energy levels as being empty until "occupied".)