Non-classical aromaticity KU Leuven
The shell structure is a universal architectural principle that appears in many forms of matter, from planets to atoms. At the macroscopic level, the shells correspond to a set of concentric layers, forming a spherical structure. Such is the case for the earth itself, with a nucleus, a mantle and a crust. On the atomic scale the shell concept no longer refers to layers in space, but to layers in energy. Electrons are orbiting around nuclei, ...