A chemical symbol is an abbreviation or shortened version of the name of a chemical element.

2H2 + O2 → 2H2O

Chemical symbols may also be modified by the use of superscripts or subscripts to show a specific isotope of an atom. Additionally superscripts may be used to indicate the ionization or oxidation state of an element.

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

* The nucleon number (mass number) is shown in the left superscript position (e.g., 14N)
* The proton number (atomic number) may be indicated in the left subscript position (e.g., 64Gd)
* If necessary, a state of ionization or an excited state may be indicated in the right superscript position (e.g., state of ionization Ca2+)
* The number of atoms of an element in a molecule or chemical compound is shown in the right subscript position (e.g., N2 or Fe2O3)
* A radical is indicated by a dot on the right side (e.g., Cl· for a chloride radical)

In China, each chemical element is assigned an ideograph as its symbol; most of them have been explicitly created for this purpose (see Chinese characters for chemical elements).

For complete listings of the chemical elements and their symbols, see:

* List of elements by symbol
* List of elements by name
* List of elements by number
* Periodic table of the elements