- Chemical symbol
A chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element, usually derived from the name of the element, often in Latin. Only the first letter is capitalised. For example, "He" is the symbol for helium (English name, not known in ancient Roman times), "Pb" for lead (plumbum in Latin), "W" for tungsten (wolfram in German, not known in Roman times). Temporary symbols assigned to newly or not-yet synthesized elements use 3-letter symbols based on their atomic numbers. For example, "Uno" was the temporary symbol for Hassium which had the temporary name of Unniloctium.
Chemical symbols may be modified by the use of superscripts or subscripts to specify a particular 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+). In astronomy, non-ionised atomic hydrogen is often known as "HI", and ionised hydrogen as "HII".
- 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)
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
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