Symbol (chemistry)

In chemistry, a symbol is a code for a chemical element.^{[nb 1]} Chemical symbols usually two letters long, but can be three depending on whether or not the element has a name yet, and are written with only the first letter capitalized.

Chemical symbols often resemble classical Latin and Greek vocabulary. For some elements, this is because the material was known in ancient times, while for others, the name is a more recent invention. For example, "He" is the symbol for helium (New Latin name, not known in ancient Roman times), "Pb" for lead (plumbum in Latin), and "Hg" for mercury (hydrargyrum in Greek). Some symbols come from other sources, like "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 (element 108) which had the temporary name of unniloctium.

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 no longer officially used.

This is an example of an atomic symbol. The text boxes explain where the numbers are derived from.

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). 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., ^99mTc). Alternately, the number here can represent a specific spin state (e.g., ¹O₂). 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., ₆₄Gd). 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 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). Often omitted if the value is one.
• A radical is indicated by a dot on the right side (e.g., Cl^• for a neutral chlorine atom). This is often omitted unless relevant to a certain context because it is already knowable from the charge and atomic number information values.

In Chinese, each chemical element has a dedicated character, usually created for the purpose (see Chemical elements in East Asian languages). However, Latin symbols are also used, especially in formulas.

The periodic table, elements being denoted by their symbols

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.

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 and names not currently used

The following is a list of symbols and names 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 Chinese characters for elements. Modern alphabetic notation was introduced in 1814 by Jöns Jakob Berzelius.

Chemical symbol	Original name	Modern name	Atomic number	Origin of symbol
☉	Hydrogen	Hydrogen	1	Daltonian symbol circa 1808.
⬤	Carbon	Carbon	6	Daltonian symbol circa 1808.
⦶	Azote	Nitrogen	7	Daltonian symbol circa 1808.
◯	Oxygen	Oxygen	8	Daltonian symbol circa 1808.
⦷	Soda	Sodium	11	Daltonian symbol circa 1808.
⊛	Magnesium	Magnesium	12	Alchemical symbol.
	Sulfur	Sulfur	16	Alchemical symbol.
	Pallas	Sulfur	16	Alchemical symbol.
🜍	Sulfur	Sulfur	16	Alchemical symbol.
ⴲ	Sulfur	Sulfur	16	Daltonian symbol circa 1808.
♂	Mars	Iron	26	Alchemical symbol.
Ⓘ	Iron	Iron	26	Daltonian symbol circa 1808.
	Stellae Fixae	Copper	29	Pre–16th-century alchemical symbol.
♀	Venus	Copper	29	Alchemical symbol.
	Copper	Copper	29	Alchemical symbol.
Ⓒ	Copper	Copper	29	Daltonian symbol circa 1808.
Ⓩ	Zinc	Zinc	30	Daltonian symbol circa 1808.
	Arsenic	Arsenic	33	Alchemical symbol.
🜺	Arsenic	Arsenic	33	Alchemical symbol.
☽	Luna	Silver	47	Alchemical symbol.
🜛	Silver	Silver	47	Alchemical symbol.
Ⓢ	Silver	Silver	47	Daltonian symbol circa 1808.
♃	Iupiter	Tin	50	Alchemical symbol.
♁	Antimony	Antimony	51	Alchemical symbol.
☾	Platinum	Platinum	78	Alchemical symbol.
☉	Platinum	Platinum	78	Alchemical symbol.
⛢	Uranus	Platinum	78	Alchemical symbol.
☼	Sol	Gold	79	Alchemical symbol from the 16th century.
☉	Sol	Gold	79	Alchemical symbol from 1700 through 1783.
🜚	Gold	Gold	79	Alchemical symbol.
♓	Pisces	Mercury	80	Pre–16th-century alchemical symbol.
♆	Neptunus	Mercury	80	Alchemical symbol from the 17th century.
☿	Mercurius	Mercury	80	Alchemical symbol from 1700 through 1783.
♄	Saturnus	Lead	82	Alchemical symbol circa 1783.
Ⓛ	Lead	Lead	82	Daltonian symbol circa 1808.
♉	Taurus	Bismuth	83	Alchemical symbol.

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.^[5]

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.^[6]

Other symbols

See also Skeletal formula § Pseudoelement symbols.

General:

From organic chemistry:

Exotic atoms:

See also

• List of chemical elements naming controversies
• List of elements
• Nuclear notation

Notes

1. ↑ 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.
2. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 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.
3. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 The isotopic composition of this element varies in some geological specimens, and the variation may exceed the uncertainty stated in the table.
4. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 The isotopic composition varies in terrestrial material such that a more precise atomic weight can not be given.
5. 1 2 3 4 5 6 7 8 The isotopic composition of the element can vary in commercial materials, which can cause the atomic weight to deviate significantly from the given value.
6. ↑ The atomic weight of commercial lithium can vary between 6.939 and 6.996. Analysis of the specific material is necessary to find a more accurate value.
7. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 Name changed due to a standardization of, modernization of, or update to older formerly-used symbol.
8. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 Name designated by discredited/disputed claimant.
9. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 Name proposed prior to discovery/creation of element or prior to official re-naming of a placeholder name.
10. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 Temporary placeholder name.

References

• Element name etymologies. Retrieved July 15, 2005.
• Atomic Weights of the Elements 2001, Pure Appl. Chem. 75(8), 1107–1122, 2003. Retrieved June 30, 2005. Atomic weights of elements with atomic numbers from 1–109 taken from this source.
• IUPAC Standard Atomic Weights Revised (2005).
• WebElements Periodic Table. Retrieved June 30, 2005. Atomic weights of elements with atomic numbers 110–116 taken from this source.
• Lapp, Ralph E. Matter. Life Science Library. New York: Time, Inc. 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