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Bohr model in 1921 [4] after Sommerfeld expansion of 1913 model showing maximum electrons per shell with shells labeled in X-ray notation. Until the second decade of the 20th century, atomic models were generally speculative. Even the concept of atoms, let alone atoms with internal structure, faced opposition from some scientists. [5]: 2
The shell terminology comes from Arnold Sommerfeld's modification of the 1913 Bohr model. During this period Bohr was working with Walther Kossel, whose papers in 1914 and in 1916 called the orbits "shells". [5] [6] Sommerfeld retained Bohr's planetary model, but added mildly elliptical orbits (characterized by additional quantum numbers ℓ ...
Electron configuration was first conceived under the Bohr model of the atom, and it is still common to speak of shells and subshells despite the advances in understanding of the quantum-mechanical nature of electrons. An electron shell is the set of allowed states that share the same principal quantum number, n, that electrons may occupy.
Electron shells are made up of one or more electron subshells, or sublevels, which have two or more orbitals with the same angular momentum quantum number l. Electron shells make up the electron configuration of an atom. It can be shown that the number of electrons that can reside in a shell is equal to .
Description: Stylised atom. Blue dots are electrons, red dots are protons and black dots are neutrons. Date: 14 February 2007: Source: Own work based on: of Image:Stylised Lithium Atom.png by Halfdan.
English: Diagram showing the maximum number of electrons on the K, L and M shells (this does not correspond to any existing atom). Français : Diagramme montrant le nombre maximum d'électrons sur les couches K, L et M (cela ne correspond à aucun atome réel).
A lithium atom is an atom of the chemical element lithium. Stable lithium is composed of three electrons bound by the electromagnetic force to a nucleus containing three protons along with either three or four neutrons , depending on the isotope , held together by the strong force .
The expression "shell model" is ambiguous in that it refers to two different items. It was previously used to describe the existence of nucleon shells according to an approach closer to what is now called mean field theory. Nowadays, it refers to a formalism analogous to the configuration interaction formalism used in quantum chemistry.