Symbol (chemistry)

A chemical symbol is a code for a chemical element. It is usually derived from the name of the element, often in Latin.

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). Only the first letter is capitalized. 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 and "Uuo" is the symbol for ununoctium (temporary name) with the atomic mass 118.

Chemical symbols may be modified by the use of prepended superscripts or subscripts to specify a particular isotope of an atom. Additionally, appended superscripts may be used to indicate the ionization or oxidation state of an element. They are widely used in chemistry and they have been officially chosen by the International Union of Pure and Applied Chemistry. There are also some historical symbols that are currently not official any more.

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 "H I", and ionised hydrogen as "H II".
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., ClÂ· for a chloride radical)

In Chinese each chemical element has an ideograph, usually created for the purpose, as its symbol (see Chemical elements in East Asian languages).

A list of current, dated, as well as proposed and historical signs and symbols is included here with its 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.

Current symbols

Antimatter atoms are denoted by a bar above the symbol for their matter counterpart, so e.g. H is the symbol for antihydrogen.

Symbols not currently used

The following is a list of symbols formerly used or suggested for elements, including symbols for placeholder names and names given by discredited claimants for discovery.

Pictographic symbols

The following is a list of pictographic symbols employed to symbolize elements known since ancient times (for example to the alchemists). Not included in this list are symbolic representations of substances previously called elements (such as certain rare earth mineral blends and the classical elements fire and water of ancient philosophy) which are known today to be multi-atomic. Also not included are symbolic representations currently used for elements in other languages such as the Traditional Chinese elements. Modern alphabetic notation was introduced in 1814 by JÃ¶ns Jakob Berzelius.

Symbols for named isotopes

The following is a list of isotopes of elements given in the previous tables which have been designated unique symbols. By this it is meant that a comprehensive list of current systematic symbols (in the ^uAtom form) are not included in the list and can instead be found in the Isotope index chart. The symbols for the named isotopes of hydrogen, deuterium (D) and tritium (T) are still in use today. Heavy water and other deuterated solvents are commonly used in chemistry, and it is convenient to use a single character rather than a symbol with a subscript in these cases. The practice also continues with tritium compounds. When the name of the solvent is given, a lowercase d is sometimes used. For example, d₆-benzene and C₆D₆ can be used instead of [²H₆]C₆H₆.

The symbols for isotopes of elements other than hydrogen are no longer in use within the scientific community. Many of these symbols were designated during the early years of radiochemistry, and several isotopes (namely those in the actinium decay family, the radium decay family, and the thorium decay family) bear placeholder names using the early naming system devised by Ernest Rutherford.

Other symbols

General:

From organic chemistry:

From inorganic chemistry:

Notes

^ This should not be confused with formula. When a number is present at the bottom right corner of the symbol of the element, only then is it said to be a formula, but if the number is not present, it is a symbol.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak The element does not have any stable nuclides, and a value in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However, three elements, thorium, protactinium, and uranium, have a characteristic terrestrial isotopic composition, and thus their atomic mass given.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am The isotopic composition of this element varies in some geological specimens, and the variation may exceed the uncertainty stated in the table.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o The isotopic composition varies in terrestrial material such that a more precise atomic weight can not be given.
^ ^a ^b ^c ^d ^e ^f ^g ^h The isotopic composition of the element can vary in commercial materials, which can cause the atomic weight to deviate significantly from the given value.
^ The atomic weight of commercial Lithium can vary between 6.939 and 6.996â€"analysis of the specific material is necessary to find a more accurate value.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x ^y ^z ^aa ^ab ^ac ^ad ^ae ^af ^ag ^ah ^ai ^aj ^ak ^al ^am ^an ^ao ^ap ^aq ^ar ^as Name changed due to a standardization of, modernization of, or update to older formerly-used symbol.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o Name designated by discredited/disputed claimant.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t ^u ^v ^w ^x Name proposed prior to discovery/creation of element or prior to official re-naming of a placeholder name.
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s Temporary placeholder name.

References

Element name etymologies. Retrieved July 15, 2005.
Atomic Weights of the Elements 2001, Pure Appl. Chem. 75(8), 1107â€"1122, 2003. Retrieved June 30, 2005. Atomic weights of elements with atomic numbers from 1â€"109 taken from this source.
IUPAC Standard Atomic Weights Revised (2005).
WebElements Periodic Table. Retrieved June 30, 2005. Atomic weights of elements with atomic numbers 110â€"116 taken from this source.
Lapp, Ralph E. Matter. Life Science Library. New York: Time Incorporated. 1963.
Leighton, Robert B. Principles of Modern Physics. New York: McGraw-Hill. 1959.
Scerri, E.R. "The Periodic Table, Its Story and Its Significance". New York, Oxford University Press. 2007.

External links

Berzelius' List of Elements
History of IUPAC Atomic Weight Values (1883 to 1997)
American Chemical Society, Committee on Nomenclature, Terminology & Symbols

Symbol (chemistry)

Monday, April 20, 2015