Historical symbolic representation of element
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In chemistry, a symbol is an abbreviation for a chemical element. Symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.
Earlier symbols for chemical elements stem from 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, Pb is the symbol for lead (plumbum in Latin); Hg is the symbol for mercury (hydrargyrum in Greek); and He is the symbol for helium (a new Latin name) because helium was not known in ancient Roman times. Some symbols come from other sources, like W for tungsten (Wolfram in German) which was not known in Roman times.
A 3-letter temporary symbol may be assigned to a newly synthesized (or not-yet synthesized) element. For example, "Uno" was the temporary symbol for hassium (element 108) which had the temporary name of unniloctium, based on its atomic number being 8 greater than 100. There are also some historical symbols that are no longer officially used.
In addition to the letters for the element itself, additional details may be added to the symbol as superscripts or subscripts a particular isotope, ionization or oxidation state, or other atomic detail.[1] A few isotopes have their own specific symbols rather than just an isotopic detail added to their element symbol.
Annotated example of an atomic 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., 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). If this number is one, it is normally omitted - the number one is implicitly understood if unspecified.
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 deducible from the charge and atomic number, as generally true for nonbonded valence electrons in skeletal structures.
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.
Many functional groups also have their own chemical symbol, e.g. Ph for the phenyl group, and Me for the methyl group.
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.
Hazard pictographs are another type of symbols used in chemistry.