Editing Chemical symbol (section)

==Extension of the symbol==
[[File:Atomic Symbol Mg.svg|thumb|upright=1.5|Annotated example of an atomic symbol]]
In addition to the letters for the element itself, additional details may be added to the symbol as [[subscript and superscript|superscripts or subscripts]] a particular [[isotope]], [[ionization]], or [[oxidation state]], or other atomic detail.<ref>{{cite report |url= http://old.iupac.org/reports/provisional/abstract04/RB-prs310804/Chap3-3.04.pdf |title= IUPAC Provisional Recommendations: IR-3: Elements and Groups of Elements |date= March 2004 |publisher= [[IUPAC]]}}</ref> A few isotopes have their own specific symbols rather than just an isotopic detail added to their element symbol.

Attached subscripts or superscripts specifying a nuclide or molecule have the following meanings and positions:

*The [[nucleon]] number ([[mass number]]) is shown in the left superscript position (e.g., <sup>14</sup>N). This number defines the specific isotope. Various letters, such as "m" and "f" may also be used here to indicate a [[nuclear isomer]] (e.g., [[technetium-99m|<sup>99m</sup>Tc]]). Alternately, the number here can represent a specific [[quantum state|spin state]] (e.g., [[singlet oxygen|<sup>1</sup>O<sub>2</sub>]]). These details can be omitted if not relevant in a certain context.
*The proton number ([[atomic number]]) may be indicated in the left subscript position (e.g., <sub>64</sub>Gd). The atomic number is redundant to the chemical element, but is sometimes used to emphasize the change of numbers of nucleons in a nuclear reaction.
*If necessary, a state of [[ionization]] or an [[excited state]] may be indicated in the right superscript position (e.g., state of ionization Ca<sup>2+</sup>).
*The number of atoms of an element in a [[molecule]] or [[chemical compound]] is shown in the right subscript position (e.g., N<sub>2</sub> or Fe<sub>2</sub>O<sub>3</sub>). If this number is one, it is normally omitted - the number one is implicitly understood if unspecified.
*A [[radical (chemistry)|radical]] is indicated by a dot on the right side (e.g., Cl<sup>•</sup> for a neutral chlorine atom). This is often omitted unless relevant to a certain context because it is already deducible from the charge and atomic number, as generally true for nonbonded valence electrons in [[skeletal structure]]s.

Many [[functional group]]s also have their own chemical symbol, e.g. Ph for the [[phenyl group]], and Me for the [[methyl group]].

A list of current, dated, as well as proposed and historical signs and symbols is included here with its [[definition|signification]]. Also given is each element's [[atomic number]], [[atomic weight]], or the [[atomic mass]] of the most stable [[isotope]], group and period numbers on the [[periodic table]], and [[etymology]] of the symbol.