Physical Science

Niels Bohr proposed that electrons inside an atom occupy only certain allowed orbitals with a specific energy. In other words, the energy of an electron in an atom is not continuous, but 'quantized.' The energies corresponding to each of the allowed orbitals are called energy levels or shell levels.

 

 Electrons are found in areas called shells. A shell is sometimes called anenergy level.
 Shells are areas that surround the center of an atom.

Each of those shells has a name (K, L, M...).