Chemical symbol

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, also known as atomic symbols, normally consist of one or two letters from the Latin alphabet and are written with the first letter capitalised.

History

Earlier symbols for chemical elements stem from classical Latin and Greek words. 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 ; Hg is the symbol for mercury ; and He is the symbol for helium because helium was not known in ancient Roman times. Some symbols come from other sources, like W for tungsten which was not known in Roman times.
A three-letter temporary symbol may be assigned to a newly synthesized element. For example, "Uno" was the temporary symbol for hassium 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.

Extension of the symbol

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. 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 is shown in the left superscript position. This number defines the specific isotope. Various letters, such as "m" and "f" may also be used here to indicate a nuclear isomer. Alternately, the number here can represent a specific spin state. These details can be omitted if not relevant in a certain context.
The proton number may be indicated in the left subscript position. 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.
The number of atoms of an element in a molecule or chemical compound is shown in the right subscript position. 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. 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.

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.

Symbol	Name	Atomic number	Notes	Why not used	Refs
A	Argon	18	A used for Argon until 1957. Current symbol is Ar.
Ab	Alabamine	85	Discredited claim to discovery of astatine.
Ad	Aldebaranium	70	Former name for ytterbium.
Ah	Anglohelvetium	85	Discredited claim to discovery of astatine.
Ak	Alkalinium	87	Discredited claim to discovery of francium.
Am	Alabamine	85	Discredited claim to discovery of astatine. The symbol Am is now used for americium.
An	Athenium	99	Proposed name for einsteinium.
Ao	Ausonium	93	Discredited claim to discovery of neptunium.
At	Austriacum	84	Discredited claim to discovery of polonium. The symbol At is now used for astatine.
Az	Azote	7	Former name for nitrogen.
Bo	Bohemium	93	Discredited claim to discovery of neptunium.
Bo	Boron	5	Current symbol is B.
Bv	Brevium	91	Former name for protactinium-234.
Bz	Berzelium	90	Baskerville wrongly believed berzelium was a new element. Was actually thorium.
Cb	Columbium	41	Former name for niobium.
Ch	Chromium	24	Current symbol is Cr.
Cl	Columbium	41	Former name for niobium. The symbol Cl is now used for chlorine.
Cm	Catium	87	Proposed name for francium. The symbol Cm is now used for curium.
Cn	Carolinium	90	Baskerville wrongly believed carolinium to be a new element. Was actually thorium. The symbol Cn is now used for copernicium.
Cp	Cassiopeium	71	Former name for lutetium.
Cp	Copernicium	112	Current symbol is Cn.
Ct	Celtium	72	Discredited claim to discovery of hafnium.
Ct	Centurium	100	Proposed name for fermium.
Cy	Cyclonium	61	Proposed name for promethium.
D	Didymium	59/60	Mixture of the elements praseodymium and neodymium. Mosander wrongly believed didymium to be an element.
Da	Davyum	43	Discredited claim to discovery of technetium.
Db	Dubhium	69	Eder wrongly believed dubhium to be a new element. Was actually thulium. The symbol Db is now used for dubnium.
Db	Dubnium	104	Proposed name for rutherfordium. The symbol and name were instead used for element 105.
Dc	Decipium	62	Delafontaine wrongly believed decipium to be a new element. Was actually samarium.
Dc	Dvicaesium	87	Name given by Mendeleev to an as of then undiscovered element. When discovered, francium closely matched the prediction.
De	Denebium	69	Eder wrongly believed denebium to be a new element. Was actually thulium.
Di	Didymium	59/60	Mixture of the elements praseodymium and neodymium. Mosander wrongly believed didymium to be an element.
Do	Dor	85	Discredited claim to discovery of astatine made by Horia Hulubei and Yvette Cauchois.
Dn	Dubnadium	118	Proposed name for oganesson.
Dp	Decipium	62	Delafontaine wrongly believed decipium to be a new element. Was actually samarium.
Ds	Dysprosium	66	Current symbol is Dy. The symbol Ds is now used for darmstadtium.
Dt	Dvitellurium	84	Name given by Mendeleev to an as of then undiscovered element. When discovered, polonium closely matched the prediction.
E	Einsteinium	99	Current symbol is Es.
E	Erbium	68	Current symbol is Er.
Ea	Ekaaluminium	31	Name given by Mendeleev to an as of then undiscovered element. When discovered, gallium closely matched the prediction.
Eb	Ekaboron	21	Name given by Mendeleev to an as of then undiscovered element. When discovered, scandium closely matched the prediction.
Eb	Erebodium	42	Alexander Pringle wrongly believed erebodium to be a new element. Was likely molybdenum.
El	Ekaaluminium	31	Name given by Mendeleev to an as of then undiscovered element. When discovered, gallium closely matched the prediction.
Em	Ekamanganese	43	Name given by Mendeleev to an as of then undiscovered element. When discovered, technetium closely matched the prediction.
Em	Emanation	86	Also called "radium emanation", the name was originally given by Friedrich Ernst Dorn in 1900. In 1923, this element officially became radon.
Em	Emanium	89	Alternate name formerly proposed for actinium.
Es	Ekasilicon	32	Name given by Mendeleev to a then undiscovered element. When discovered, germanium closely matched the prediction. The symbol Es is now used for einsteinium.
Hs	Hesperium	94	Discredited claim to discovery of plutonium. The symbol Hs is now used for hassium.
Et	Ekatantalum	91	Name given by Mendeleev to an as of then undiscovered element. When discovered, protactinium closely matched the prediction.
Ex	Euxenium	72	Discredited claim to discovery of hafnium.
Fa	Francium	87	Current symbol is Fr.
Fl	Florentium	61	Discredited claim to discovery of promethium. The symbol Fl is now used for flerovium.
Fl	Fluorine	9	Current symbol is F. The symbol Fl is now used for flerovium.
Fr	Florentium	61	Discredited claim to discovery of promethium. The symbol Fr is now used for francium.
G	Glucinium	4	Former name for beryllium.
Gh	Ghiorsium	118	Discredited claim to discovery of oganesson.
Gl	Glucinium	4	Former name for beryllium.
Ha	Hahnium	105	Proposed name for dubnium.
Hn	Hahnium	108	Proposed name for hassium.
Hv	Helvetium	85	Discredited claim to discovery of astatine.
Hy	Mercury	80	Hy from the Greek hydrargyrum for "liquid silver". Current symbol is Hg.
I	Iridium	77	Current symbol is Ir. The symbol I is now used for iodine.
Ic	Incognitium	65	Demarçay wrongly believed incognitium to be a new element. Was actually terbium mixed with gadolinium.
Il	Illinium	61	Discredited claim to discovery of promethium.
Il	Ilmenium	41/73	Mixture of the elements niobium and tantalum. R. Hermann wrongly believed ilmenium to be an element.
Io	Ionium	65	Demarçay wrongly believed ionium to be a new element. Was actually terbium.
J	Jodium	53	Former name for iodine.
Jg	Jargonium	72	Discredited claim to discovery of hafnium.
Jl	Joliotium	105	Proposed name for dubnium.
Jp	Japonium	113	Proposed name for nihonium.
Ka	Potassium	19	Current symbol is K.
Ku	Kurchatovium	104	Proposed name for rutherfordium.
L	Lithium	3	Current symbol is Li.
Lw	Lawrencium	103	Current symbol is Lr.
M	Muriaticum	17	Former name for chlorine.
Ma	Manganese	25	Current symbol is Mn.
Ma	Masurium	43	Disputed claim to discovery of technetium.
Md	Mendelevium	97	Proposed name for berkelium. The symbol and name were later used for element 101.
Ml	Moldavium	87	Discredited claim to discovery of francium made by Horia Hulubei and Yvette Cauchois.
Ms	Magnesium	12	Current symbol is Mg.
Ms	Masrium	88	Discredited claim to discovery of radium.
Ms	Masurium	43	Disputed claim to discovery of technetium.
Ms	Mosandrium	65	Smith wrongly believed mosandrium to be a new element. Was actually terbium.
Mv	Mendelevium	101	Current symbol is Md.
Ng	Norwegium	72	Discredited claim to discovery of hafnium.
No	Norium	72	Discredited claim to discovery of hafnium. The symbol No is now used for nobelium.
Np	Neptunium	91	Discredited claim to discovery of protactinium. The symbol and name were later used for element 93.
Np	Nipponium	43	Discredited claim to discovery of technetium. The symbol Np is now used for neptunium.
Ns	Nielsbohrium	105	Proposed name for dubnium.
Ns	Nielsbohrium	107	Proposed name for bohrium.
Nt	Niton	86	Former name for radon.
Ny	Neoytterbium	70	Former name for ytterbium.
P	Lead	82	Current symbol is Pb. The symbol P is now used for phosphorus.
Pa	Palladium	46	Current symbol is Pd. The symbol Pa is now used for protactinium.
Pe	Pelopium	41	Former name for niobium.
Ph	Phosphorus	15	Current symbol is P.
Pl	Palladium	46	Current symbol is Pd.
Pm	Polymnestum	33	Alexander Pringle wrongly believed polymnestum to be a new element. Was likely arsenic. The symbol Pm is now used for promethium.
Po	Potassium	19	Current symbol is K. The symbol Po is now used for polonium.
Pp	Philippium	67	Delafontaine discovered a new element and named it philippium. Per Teodor Cleve isolated it and renamed it holmium.
R	Rhodium	45	Current symbol is Rh.
Rd	Radium	88	Current symbol is Ra.
Rf	Rutherfordium	106	Proposed name for seaborgium. The symbol and name were instead used for element 104.
Ro	Rhodium	45	Current symbol is Rh.
Sa	Samarium	62	Current symbol is Sm.
So	Sodium	11	Current symbol is Na.
Sq	Sequanium	93	Discredited claim to discovery of neptunium made by Horia Hulubei and Yvette Cauchois.
St	Antimony	51	Current symbol is Sb.
St	Tin	50	Current symbol is Sn.
Tm	Trimanganese	75	Name given by Mendeleev to an as of then undiscovered element. When discovered, rhenium closely matched the prediction. The symbol Tm is now used for thulium.
Tn	Tungsten	74	Current symbol is W.
Tr	Terbium	65	Current symbol is Tb.
Tu	Thulium	69	Current symbol is Tm.
Tu	Tungsten	74	Current symbol is W.
Ur	Uralium	75	Discredited claim to discovery of rhenium.
Ur	Uranium	92	Current symbol is U.
Vc	Victorium	64	Crookes wrongly believed victorium to be a new element. Was actually gadolinium.
Vi	Victorium	64	Crookes wrongly believed victorium to be a new element. Was actually gadolinium.
Vi	Virginium	87	Discredited claim to discovery of francium.
Vm	Virginium	87	Discredited claim to discovery of francium.
Va	Vanadium	23	Current symbol is V.
Wo	Wolfram	74	Former name for tungsten.
X	Xenon	54	Current symbol is Xe. The symbol X is now used for any halogen.
Yt	Yttrium	39	Current symbol is Y.

Systematic chemical symbols

These symbols are based on systematic element names, which are now replaced by trivial element names and symbols. Data is given in order of: atomic number, systematic symbol, systematic name; trivial symbol, trivial name.

101: Unu, unnilunium; Md, mendelevium.
102: Unb, unnilbium; No, nobelium.
103: Unt, unniltrium; Lr, lawrencium.
104: Unq, unnilquadium; Rf, rutherfordium.
105: Unp, unnilpentium; Db, dubnium.
106: Unh, unnilhexium; Sg, seaborgium.
107: Uns, unnilseptium; Bh, bohrium.
108: Uno, unniloctium; Hs, hassium.
109: Une, unnilennium; Mt, meitnerium.
110: Uun, ununnilium; Ds, darmstadtium.
111: Uuu, unununium; Rg, roentgenium.
112: Uub, ununbium; Cn, copernicium.
113: Uut, ununtrium; Nh, nihonium.
114: Uuq, ununquadium; Fl, flerovium.
115: Uup, ununpentium; Mc, moscovium.
116: Uuh, ununhexium; Lv, livermorium.
117: Uus, ununseptium; Ts, tennessine.
118: Uuo, ununoctium; Og, oganesson.

When elements beyond oganesson, are discovered; their systematic name and symbol will presumably be superseded by a trivial name and symbol.

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.
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 and saturnism.

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 symbols for 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.
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.

Symbols for named isotopes

The following is a list of isotopes which have been given unique symbols. This is not a list of current systematic symbols ; such a list can instead be found in Template:Navbox element isotopes. The symbols for isotopes of hydrogen, deuterium and tritium, are still in use today, as is thoron for radon-220. 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 superscript 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, d-benzene or CD can be used instead of C.
The symbols for isotopes of elements other than hydrogen and radon are no longer used in the scientific community. Many of these symbols were designated during the early years of radiochemistry, and several isotopes bear placeholder names using the early naming system devised by Ernest Rutherford.

Symbol	Name	Atomic number	Origin of symbol
Ac	Actinium	89	From Greek aktinos. Name restricted at one time to Ac, an isotope of actinium. This named isotope later became the official name for element 89.
AcA	Actinium A	84	From actinium and A. Placeholder name given at one time to Po, an isotope of polonium identified in the decay chain of actinium.
AcB	Actinium B	82	From actinium and B. Placeholder name given at one time to Pb, an isotope of lead identified in the decay chain of actinium.
AcC	Actinium C	83	From actinium and C. Placeholder name given at one time to Bi, an isotope of bismuth identified in the decay chain of actinium.
AcC′	Actinium C′	84	From actinium and C′. Placeholder name given at one time to Po, an isotope of polonium identified in the decay chain of actinium.
AcC″	Actinium C″	81	From actinium and C″. Placeholder name given at one time to ²⁰⁷Tl, an isotope of thallium identified in the decay chain of actinium.
AcK	Actinium K	87	Name given at one time to ²²³Fr, an isotope of francium identified in the decay chain of actinium.
AcU	Actino-uranium	92	Name given at one time to ²³⁵U, an isotope of uranium.
AcX	Actinium X	88	Name given at one time to ²²³Ra, an isotope of radium identified in the decay chain of actinium.
An	Actinon	86	From actinium and emanation. Name given at one time to ²¹⁹Rn, an isotope of radon identified in the decay chain of actinium.
D	Deuterium	1	From the Greek deuteros. Name given to ²H.
Io	Ionium	90	Name given to ²³⁰Th, an isotope of thorium identified in the decay chain of uranium.
MsTh₁	Mesothorium 1	88	Name given at one time to ²²⁸Ra, an isotope of radium.
MsTh₂	Mesothorium 2	89	Name given at one time to ²²⁸Ac, an isotope of actinium.
Pa	Protactinium	91	From the Greek protos and actinium. Name restricted at one time to ²³¹Pa, an isotope of protactinium. This named isotope later became the official name for element 91.
Ra	Radium	88	From the Latin radius. Name restricted at one time to ²²⁶Ra, an isotope of radium. This named isotope later became the official name for element 88.
RaA	Radium A	84	From radium and A. Placeholder name given at one time to ²¹⁸Po, an isotope of polonium identified in the decay chain of radium.
RaB	Radium B	82	From radium and B. Placeholder name given at one time to ²¹⁴Pb, an isotope of lead identified in the decay chain of radium.
RaC	Radium C	83	From radium and C. Placeholder name given at one time to ²¹⁴Bi, an isotope of bismuth identified in the decay chain of radium.
RaC′	Radium C′	84	From radium and C′. Placeholder name given at one time to ²¹⁴Po, an isotope of polonium identified in the decay chain of radium.
RaC″	Radium C″	81	From radium and C″. Placeholder name given at one time to ²¹⁰Tl, an isotope of thallium identified in the decay chain of radium.
RaD	Radium D	82	From radium and D. Placeholder name given at one time to ²¹⁰Pb, an isotope of lead identified in the decay chain of radium.
RaE	Radium E	83	From radium and E. Placeholder name given at one time to ²¹⁰Bi, an isotope of bismuth identified in the decay chain of radium.
RaE″	Radium E″	81	From radium and E″. Placeholder name given at one time to ²⁰⁶Tl, an isotope of thallium identified in the decay chain of radium.
RaF	Radium F	84	From radium and F. Placeholder name given at one time to ²¹⁰Po, an isotope of polonium identified in the decay chain of radium.
RdAc	Radioactinium	90	Name given at one time to ²²⁷Th, an isotope of thorium.
RdTh	Radiothorium	90	Name given at one time to ²²⁸Th, an isotope of thorium.
Rn	Radon	86	From radium and emanation. Name restricted at one time to ²²²Rn, an isotope of radon identified in the decay chain of radium. This named isotope later became the official name for element 86 in 1923.
T	Tritium	1	From the Greek tritos. Name given to ³H.
Th	Thorium	90	After Thor. Name restricted at one time to ²³²Th, an isotope of thorium. This named isotope later became the official name for element 90.
ThA	Thorium A	84	From thorium and A. Placeholder name given at one time to ²¹⁶Po, an isotope of polonium identified in the decay chain of thorium.
ThB	Thorium B	82	From thorium and B. Placeholder name given at one time to ²¹²Pb, an isotope of lead identified in the decay chain of thorium.
ThC	Thorium C	83	From thorium and C. Placeholder name given at one time to ²¹²Bi, an isotope of bismuth identified in the decay chain of thorium.
ThC′	Thorium C′	84	From thorium and C′. Placeholder name given at one time to ²¹²Po, an isotope of polonium identified in the decay chain of thorium.
ThC″	Thorium C″	81	From thorium and C″. Placeholder name given at one time to ²⁰⁸Tl, an isotope of thallium identified in the decay chain of thorium.
ThX	Thorium X	88	Name given at one time to ²²⁴Ra, an isotope of radium identified in the decay chain of thorium.
Tn	Thoron	86	From thorium and emanation. Name given to ²²⁰Rn, an isotope of radon identified in the decay chain of thorium.
UI	Uranium I	92	Name given at one time to ²³⁸U, an isotope of uranium.
UII	Uranium II	92	Name given at one time to ²³⁴U, an isotope of uranium.
UX₁	Uranium X₁	90	Name given at one time to ²³⁴Th, an isotope of thorium identified in the decay chain of uranium.
UX₂	Uranium X₂	91	Name given at one time to ^234mPa, an isotope of protactinium identified in the decay chain of uranium.
UY	Uranium Y	90	Name given at one time to ²³¹Th, an isotope of thorium identified in the decay chain of uranium.
UZ	Uranium Z	91	Name given at one time to ²³⁴Pa, an isotope of protactinium identified in the decay chain of uranium.

Other symbols

In Chinese, each chemical element has a dedicated character, usually created for the purpose. However, in Chinese Latin symbols are also used, especially in formulas.

General:

A: A deprotonated acid or an anion
An: any actinide
B: A base, often in the context of Lewis acid–base theory or Brønsted–Lowry acid–base theory
E: any element or electrophile
L: any ligand
Ln: any lanthanide
M: any metal
Mm: mischmetal
Ng: any noble gas
Nu: any nucleophile
R: any unspecified radical not important to the discussion
St: steel
X: any halogen

From organic chemistry:

Ac: acetyl –
Ad: 1-adamantyl
All: allyl
Am: amyl –
Ar: aryl –
Bn: benzyl
Bs: brosyl or benzenesulfonyl
Bu: butyl
Bz: benzoyl
Cp: cyclopentadienyl
Cp*: pentamethylcyclopentadienyl
Cy: cyclohexyl
Cyp: cyclopentyl
Et: ethyl
Me: methyl
Mes: mesityl
Ms: mesyl
Np: neopentyl –
Ns: nosyl
Pent: pentyl
Ph, Φ: phenyl
Pr: propyl –
R: In organic chemistry contexts, an unspecified "R" is often understood to be an alkyl group
Tf: triflyl
Tr, Trt: trityl
Ts, Tos: tosyl –
Vi: vinyl

From organometallic chemistry:

Fc, ferrocenyl:
Fp, (Cyclopentadienyl)iron dicarbonyl:

Exotic atoms: