Chemical symbols are the abbreviations used in chemistry, mainly for chemical elements; but also for functional groups, chemical compounds, and other entities. Element symbols for chemical elements normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

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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 Neo-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 three-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 the digits of its atomic number. 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.

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.

Many functional groups also have their own chemical symbol, e.g. Ph for the phenyl group, and Me for the methyl group.

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.

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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.

Alchemical symbols

Main article: alchemical symbols

The following ideographic symbols were used in alchemy to denote elements known since ancient times. Not included in this list are spurious elements, such as the classical elements fire and water or phlogiston, and substances now known to be compounds. Many more symbols were in at least sporadic use: one early 17th-century alchemical manuscript lists 22 symbols for mercury alone.^[10]

Planetary names and symbols for the metals – the seven planets and seven metals known since Classical times in Europe and the Mideast – was ubiquitous in alchemy. The association of what are anachronistically known as planetary metals started breaking down with the discovery of antimony, bismuth and zinc in the 16th century. Alchemists would typically call the metals by their planetary names, e.g. "Saturn" for lead and "Mars" for iron; compounds of tin, iron and silver continued to be called "jovial", "martial" and "lunar"; or "of Jupiter", "of Mars" and "of the moon", through the 17th century. The tradition remains today with the name of the element mercury, where chemists decided the planetary name was preferable to common names like "quicksilver", and in a few archaic terms such as lunar caustic (silver nitrate) and saturnism (lead poisoning).^[10]

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Alchemical symbols for the modern elements

Symbol		Element	Atomic number	Notes
		Phosphorus	15	(discovered late)
	🜍	Sulfur	16	used by Newton
		Manganese	25	late; used by Torbern Bergman (1775)
	♂	Iron	26	classical planetary metal of Mars
	🜶	Cobalt	27	late; used by Bergman
		Nickel	28	late; used by Bergman (old positional variant of arsenic, previously used for regulus of sulfur)
		Zinc	30	late; used by Bergman
	♀	Copper	29	classical planetary metal of Venus
	🜺	Arsenic	33
	☾	Silver	47	classical planetary metal of the Moon
	🜛
	♃	Tin	50	classical planetary metal of Jupiter
	♁	Antimony	51	the newly discovered "eighth metal" was given the symbol for the Earth, which was recognized as a planet by that time
		Platinum	78	late; used by Bergman et al.: a compound of ☉ gold and ☾ silver
	⛢			late; symbol invented for the newly discovered planet Uranus
	🜚	Gold	79	classical variant
	☉			medieval variant; planetary metal for the Sun
	☿	Mercury	80	classical planetary metal for Mercury
	♄	Lead	82	classical planetary metal for Saturn
	♆	Bismuth	83	used by Newton
	♉︎			used by Bergman

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Daltonian symbols

The following symbols were employed by John Dalton in the early 1800s as the periodic table of elements was being formulated. Not included in this list are substances now known to be compounds, such as certain rare-earth mineral blends. Modern alphabetic notation was introduced in 1814 by Jöns Jakob Berzelius; its precursor can be seen in Dalton's circled letters for the metals, especially in his augmented table from 1810.^[11] A trace of Dalton's conventions also survives in ball-and-stick models of molecules, where balls for carbon are black and for oxygen red.

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Daltonian symbols for the elements

Symbol		Dalton's name	Modern name	Atomic number	Notes	Refs
img.	char.
	☉	hydrogen		1	or ⊙	[12]
		glucine	beryllium	4	alchemical symbol for 'sugar'	[13]
	●	carbone, carbon	carbon	6		[12]
	⦶	azote	nitrogen/azote	7	alchemical symbol for niter	[12]
	○	oxygen		8	or ◯	[12]
	⦷	soda	sodium	11		[12]
	⊛	magnesia	magnesium	12	alchemical symbol for magnesia	[12]
		alumine	aluminium	13	(4 dots)	[12]
	🟕	silex	silicon	14		[13]
		phosphorus		15	(3 radii)	[12]
	🜨	sulphur		16		[12]
		potash	potassium	19	(3 vertical lines)	[12]
	⦾	lime	calcium	20	or ◎	[12]
		titanium		22	(enclosing circle) Tit⃝	[13]
		manganese		25	(enclosing circle) Ma⃝	[13]
	Ⓘ	iron		26		[12]
	Ⓝ	nickel		28		[12]
		cobalt		27	(enclosing circle) Cob⃝	[13]
	Ⓒ	copper		29	(black letter in red circle)	[12]
	Ⓩ	zinc		30		[12]
		arsenic		33	(enclosing circle) Ar⃝	[13]
		strontian	strontium	38	(4 ticks)	[12]
	⊕︀︀	yttria	yttrium	39	(plus does not touch circle)	[13]
		zircone	zirconium	40	(vertical zigzag)	[13]
	Ⓢ	silver		47		[12]
	Ⓣ	tin		50		[13]
		antimony		51	(enclosing circle) An⃝	[13]
		barytes	barium	56	(6 ticks)	[12]
		cerium		58	(enclosing circle) Ce⃝	[13]
		tungsten		74	(enclosing circle) Tu⃝	[13]
	Ⓟ	platina	platinum	78	(black letter in red circle)	[12]
	Ⓖ	gold		79		[12]
		mercury		80	(dotted inside perimeter)	[12]
	Ⓛ	lead		82		[12]
	Ⓑ	bismuth		83		[13]
	Ⓤ	uranium		92		[13]

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The following is a list of isotopes which have been given unique symbols. This is not a list of current systematic symbols (in the ^uAtom form); such a list can instead be found in Template:Navbox element isotopes. The symbols for the named isotopes of hydrogen, deuterium (D), and tritium (T) are still in use today, as is thoron (Tn) for radon-220 (though not actinon; An usually instead means a generic actinide). 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 or C₆D₆ can be used instead of C₆[²H₆].^[14]

The symbols for isotopes of elements other than hydrogen and radon 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 decay chains of actinium, radium, and thorium) bear placeholder names using the early naming system devised by Ernest Rutherford.^[15]

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

General:

From organic chemistry:

Exotic atoms:

Hazard pictographs are another type of symbols used in chemistry.

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