# 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*

It assumes

fixed orbits(positions) andfixed trajectories(momenta), and such simultaneous known quantitiesthe Heisenberg Uncertainty Principle. It also does not identify quantum numbersdisobeys#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 foratom.*any*

Such orbitals are

regions of electron density, and are related to the probability densities of electron position over allspace, averaged over infinite time.

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 eachangular 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".)