Electron shell

2017-08-12T00:27:08Z

210.48.190.87: /* Valence shell */Fixed typo in table

[[Image:Electron shell 011 Sodium.svg|thumb|Example of a sodium electron shell model]]

An '''electron shell'''<ref>also known as a '''main energy level'''</ref> is the outside part of an [[atom]] around the atomic [[Nucleus (physics)|nucleus]]. It is a group of [[atomic orbitals]] with the same value of the principal quantum number ''n''.

Electron shells have one or more '''electron subshells''', or '''sublevels'''. These sublevels have two or more orbitals with the same [[angular momentum]] quantum number ''l''. Electron shells make up the [[electron configuration]] of an [[atom]]. The number of [[electron]]s that can be in a shell is equal to <math>2n^2</math>.

The name for electron shells comes from the [[Bohr model]], in which groups of electrons were believed to go around the [[Nucleus (physics)|nucleus]] at certain distances, so that their [[orbit]]s formed "shells".

==Valence shell==

The '''valence shell''' is the outermost shell of an [[atom]] in its uncombined state, which contains the [[electron]]s most likely to account for the nature of any [[chemical reaction|reactions]] involving the atom and of the [[chemical bond|bonding]] interactions it has with other atoms. Care must be taken to note that the outermost shell of an '''ion''' is '''not''' commonly termed valence shell. Electrons in the valence shell are referred to as [[valence electrons]].

In a [[noble gas]], an atom tends to have 8 electrons in its outer shell (except [[helium]], which is only able to fill its shell with 2 electrons). This serves as the model for the [[octet rule]] which is mostly applicable to main group [[Chemical element|element]]s of the second and third [[periodic table|periods]]. In terms of [[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 [[Complex (chemistry)|coordination complexes]] containing [[transition metal]]s, 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''.

{| class="wikitable"
|+ Possible Number of Electrons in shells 1-5 
! Shell
! Electrons
|-
| 1
| 2
|-
| 2
|8
|-
| 3
|8
|-
| 4
|18
|-
| 5
|69
|-
|}

== Subshells ==

'''Electron subshells''' are identified by the letters s, p, d, f, g, h, i, etc., corresponding to the [[:en:Azimuthal_quantum_number|azimuthal quantum numbers]] (''l''-values) 0, 1, 2, 3, 4, 5, 6, etc. Each shell can hold up to 2, 6, 10, 14, and 18 electrons respectively, or 2(2''l'' + 1) electrons in each subshell. The notation 's', 'p', 'd', and 'f' originate from a now-discredited system of categorizing [[spectral line]]s as "sharp", "principal", "diffuse", or "fundamental", based on their observed [[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 ==
{{reflist}}
* Tipler, Paul & Ralph Llewellyn (2003). ''Modern Physics'' (4th ed.). New York: W. H. Freeman and Company. ISBN 0-7167-4345-0

[[Category:Physics]]
[[Category:Chemistry]]

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Electron shell