Electron shell

  An electron shell, also known as a main energy level, is a group of electrons that can reside in a shell is equal to 2n^{2 [1]}.

History

The existence of electron shells was first observed experimentally in Charles Barkla's and Henry Moseley's Siegbahn notation.

The name for electron shells originates from the Bohr model, in which groups of electrons were believed to orbit the nucleus at certain distances, so that their orbits formed "shells" around the nucleus.

Valence shell

Main article: Valence electron

The valence shell is the outermost shell of an Linus Pauling later generalized and extended the theory while applying insights from quantum mechanics.

In a atomic orbitals, the electrons in the valence shell are distributed 2 in the single s orbital and 2 each in the three p orbitals.

For transition metals, the valence shell consists of electrons in these s and p orbitals, as well as up to 10 additional electrons, distributed as 2 into each of 5 d orbitals, to make a total of 18 electrons in a complete valence shell for such a compound. This is referred to as the eighteen electron rule.

Each shell can hold 2, 8, 18, or 32 electrons, or 2x² electrons in each subshell. The notation 's', 'p', 'd', and 'f' originate from a now-discredited system of categorizing fine structure. When the first four types of orbitals were described, they were associated with these spectral line types, but there were no other names. The designations 'g', 'h', and so on, were derived by following alphabetical order.

References