Chemical symbol

Chemical symbols are short abbreviations used in chemistry. They are mainly used for chemical elements, but they can also stand for functional groups, chemical compounds, and other things.

Element symbols, which are also called atomic symbols, usually have one or two letters from the Latin alphabet. The first letter is always written as a capital letter.

History

Many chemical symbols for elements come from old Latin and Greek words. Some elements were known in ancient times, so their symbols come from their old names. For example, Pb is the symbol for lead, from its Latin name plumbum. Hg is the symbol for mercury, from its Greek name hydrargyrum. He is the symbol for helium, which has a Neo-Latin name, because helium was not known in ancient Roman times. Some symbols come from other languages. For example, W is the symbol for tungsten, from its German name Wolfram. Tungsten was also not known in Roman times.

A new element may be given a three-letter temporary symbol, even if it has not yet been made. For example, "Uno" was the temporary symbol for hassium, which is element 108. Its temporary name was 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

Extra details can be added to an element's symbol to show things like a particular isotope, ionization, or oxidation state. This is done with small numbers and marks, called superscripts or subscripts. A few isotopes have their own symbols. The mass number, which counts the nucleons, goes in the top left, as in ¹⁴N. It can also show a nuclear isomer, such as ^99mTc, or a spin state, such as ¹O₂. The atomic number can go in the bottom left, as in ₆₄Gd. A state of ionization or an excited state goes in the top right, as in Ca²⁺. The number of atoms in a molecule or chemical compound goes in the bottom right, as in N₂ or Fe₂O₃. A radical is shown by a dot on the right, as in Cl^•. Details that do not matter in a certain context can be left out.

Many functional groups also have their own symbols, such as Ph for the phenyl group and Me for the methyl group. The article includes a list of current, past, and proposed symbols and their signification. It also gives each element's atomic number, atomic weight, or atomic mass of its most stable isotope, its group and period on the periodic table, and the etymology of its symbol.

Symbols for chemical elements


List of chemical elements
Z	Symbol	Name	Origin of name
1	H	Hydrogen	Greek hydro- and -gen, meaning 'water-forming'
2	He	Helium	Greek hḗlios, 'sun'
3	Li	Lithium	Greek líthos, 'stone'
4	Be	Beryllium	beryl, a mineral (ultimately from the name of Belur in southern India)
5	B	Boron	borax, a mineral (from Arabic bawraq)
6	C	Carbon	Latin carbo, 'coal'
7	N	Nitrogen	Greek nítron and -gen, meaning 'niter-forming'
8	O	Oxygen	Greek oxy- and -gen, meaning 'acid-forming'
9	F	Fluorine	Latin fluere, 'to flow'
10	Ne	Neon	Greek néon, 'new'
11	Na	Sodium	English soda (the symbol Na is derived from Neo-Latin natrium, coined from German Natron, 'natron')
12	Mg	Magnesium	Magnesia, a district of Eastern Thessaly in Greece
13	Al	Aluminium	alumina, from Latin alumen (gen. alumni), 'bitter salt, alum'
14	Si	Silicon	Latin silex, 'flint' (originally silicium)
15	P	Phosphorus	Greek phōsphóros, 'light-bearing'
16	S	Sulfur	Latin sulphur, 'brimstone'
17	Cl	Chlorine	Greek chlōrós, 'greenish yellow'
18	Ar	Argon	Greek argós, 'idle' (because of its inertness)
19	K	Potassium	Neo-Latin potassa, 'potash' (the symbol K is derived from Latin kalium)
20	Ca	Calcium	Latin calx, 'lime'
21	Sc	Scandium	Latin Scandia, 'Scandinavia'
22	Ti	Titanium	Titans, the sons of the Earth goddess of Greek mythology
23	V	Vanadium	Vanadis, an Old Norse name for the Scandinavian goddess Freyja
24	Cr	Chromium	Greek chróma, 'colour'
25	Mn	Manganese	corrupted from magnesia negra; see Magnesium
26	Fe	Iron	English word, ultimately from Proto-Celtic īsarnom, a word related to the Celtic word for "blood" (the symbol Fe is derived from Latin ferrum*)
27	Co	Cobalt	German Kobold, 'goblin'
28	Ni	Nickel	Nickel, a mischievous sprite of German miner mythology
29	Cu	Copper	English word, from Latin cuprum, from Ancient Greek Kýpros 'Cyprus'
30	Zn	Zinc	Most likely from German Zinke, 'prong' or 'tooth', though some suggest Persian sang, 'stone'
31	Ga	Gallium	Latin Gallia, 'France'
32	Ge	Germanium	Latin Germania, 'Germany'
33	As	Arsenic	French arsenic, from Greek arsenikón 'yellow arsenic' (influenced by arsenikós, 'masculine' or 'virile'), from a West Asian wanderword ultimately from Old Iranian *zarniya-ka, 'golden'
34	Se	Selenium	Greek selḗnē, 'moon'
35	Br	Bromine	Greek brômos, 'stench'
36	Kr	Krypton	Greek kryptós, 'hidden'
37	Rb	Rubidium	Latin rubidus, 'deep red'
38	Sr	Strontium	Strontian, a village in Scotland
39	Y	Yttrium	Ytterby, a village in Sweden
40	Zr	Zirconium	zircon, a mineral
41	Nb	Niobium	Niobe, daughter of king Tantalus from Greek mythology
42	Mo	Molybdenum	Greek molýbdaina, 'piece of lead', from mólybdos, 'lead'
43	Tc	Technetium	Greek tekhnētós, 'artificial'
44	Ru	Ruthenium	Neo-Latin Ruthenia, 'Russia'
45	Rh	Rhodium	Greek rhodóeis, 'rose-coloured', from rhódon, 'rose'
46	Pd	Palladium	the asteroid Pallas, considered a planet at the time
47	Ag	Silver	English word, ultimately from Proto-Germanic silubrą (The symbol derives from Latin argentum*)
48	Cd	Cadmium	Neo-Latin cadmia, from King Kadmos
49	In	Indium	Latin indicum, 'indigo' (colour found in its spectrum)
50	Sn	Tin	English word, ultimately from Proto-Germanic tiną, perhaps meaning "shining" (The symbol derives from Latin stannum*)
51	Sb	Antimony	Latin antimonium, the origin of which is uncertain: folk etymologies suggest it is derived from Greek antí ('against') + mónos ('alone'), or Old French anti-moine, 'Monk's bane', but it could plausibly be from or related to Arabic ʾiṯmid, 'antimony', reformatted as a Latin word. (The symbol derives from Latin stibium 'stibnite'.)
52	Te	Tellurium	Latin tellus, 'the ground, earth'
53	I	Iodine	French iode, from Greek ioeidḗs, 'violet'
54	Xe	Xenon	Greek xénon, neuter form of xénos 'strange'
55	Cs	Caesium	Latin caesius, 'sky-blue'
56	Ba	Barium	Greek barýs, 'heavy'
57	La	Lanthanum	Greek lanthánein, 'to lie hidden'
58	Ce	Cerium	the dwarf planet Ceres, considered a planet at the time
59	Pr	Praseodymium	Greek prásios dídymos, 'green twin'
60	Nd	Neodymium	Greek néos dídymos, 'new twin'
61	Pm	Promethium	Prometheus of Greek mythology
62	Sm	Samarium	samarskite, a mineral named after Colonel Vasili Samarsky-Bykhovets, Russian mine official
63	Eu	Europium	Europe
64	Gd	Gadolinium	gadolinite, a mineral named after Johan Gadolin, Finnish chemist, physicist and mineralogist
65	Tb	Terbium	Ytterby, a village in Sweden
66	Dy	Dysprosium	Greek dysprósitos, 'hard to get'
67	Ho	Holmium	Neo-Latin Holmia, 'Stockholm'
68	Er	Erbium	Ytterby, a village in Sweden
69	Tm	Thulium	Thule, the ancient name for an unclear northern location
70	Yb	Ytterbium	Ytterby, a village in Sweden
71	Lu	Lutetium	Latin Lutetia, 'Paris'
72	Hf	Hafnium	Neo-Latin Hafnia, 'Copenhagen' (from Danish havn)
73	Ta	Tantalum	King Tantalus, father of Niobe from Greek mythology
74	W	Tungsten	Swedish tung sten, 'heavy stone' (The symbol is from wolfram, the old name of the tungsten mineral wolframite)
75	Re	Rhenium	Latin Rhenus, 'the Rhine'
76	Os	Osmium	Greek osmḗ, 'smell'
77	Ir	Iridium	Iris, the Greek goddess of the rainbow
78	Pt	Platinum	Spanish platina, 'little silver', from plata 'silver'
79	Au	Gold	English word, ultimately from Proto-Indo-European ǵʰl̥h₃tóm, related to "yellow" (The symbol derives from Latin aurum*)
80	Hg	Mercury	Mercury, Roman god of commerce, communication, and luck, known for his speed and mobility (The symbol is from the element's Latin name hydrargyrum, derived from Greek hydrárgyros, 'water-silver')
81	Tl	Thallium	Greek thallós, 'green shoot or twig'
82	Pb	Lead	English word, from Proto-Celtic ɸloudom, from Proto-Indo-European plewd-, “flow” (The symbol derives from Latin plumbum)
83	Bi	Bismuth	German Wismut, from weiß Masse 'white mass', unless from Arabic
84	Po	Polonium	Latin Polonia, 'Poland' (the home country of Marie Curie)
85	At	Astatine	Greek ástatos, 'unstable'
86	Rn	Radon	Radium
87	Fr	Francium	France
88	Ra	Radium	French radium, from Latin radius, 'ray'
89	Ac	Actinium	Greek aktís, 'ray'
90	Th	Thorium	Thor, the Scandinavian god of thunder
91	Pa	Protactinium	proto- (from Greek prôtos, 'first, before') + actinium, which is produced through the radioactive decay of protactinium
92	U	Uranium	Uranus, the seventh planet in the Solar System
93	Np	Neptunium	Neptune, the eighth planet in the Solar System
94	Pu	Plutonium	the dwarf planet Pluto, considered the ninth planet in the Solar System at the time
95	Am	Americium	The Americas, as the element was first synthesised on the continent, by analogy with europium
96	Cm	Curium	Pierre Curie and Marie Curie, French physicists and chemists
97	Bk	Berkelium	Berkeley, California, where the element was first synthesised, by analogy with terbium
98	Cf	Californium	California, where the element was first synthesised
99	Es	Einsteinium	Albert Einstein, German physicist
100	Fm	Fermium	Enrico Fermi, Italian physicist
101	Md	Mendelevium	Dmitri Mendeleev, Russian chemist and inventor who proposed the periodic table
102	No	Nobelium	Alfred Nobel, Swedish chemist and engineer
103	Lr	Lawrencium	Ernest O. Lawrence, American physicist
104	Rf	Rutherfordium	Ernest Rutherford, New Zealand chemist and physicist
105	Db	Dubnium	Dubna, Russia, where the Joint Institute for Nuclear Research is located
106	Sg	Seaborgium	Glenn T. Seaborg, American chemist
107	Bh	Bohrium	Niels Bohr, Danish physicist
108	Hs	Hassium	Neo-Latin Hassia, 'Hesse' (a state in Germany)
109	Mt	Meitnerium	Lise Meitner, Austrian physicist
110	Ds	Darmstadtium	Darmstadt, Germany, where the element was first synthesised
111	Rg	Roentgenium	Wilhelm Conrad Röntgen, German physicist
112	Cn	Copernicium	Nicolaus Copernicus, Polish astronomer
113	Nh	Nihonium	Japanese Nihon, 'Japan' (where the element was first synthesised)
114	Fl	Flerovium	Flerov Laboratory of Nuclear Reactions, part of JINR, where the element was synthesised; itself named after Georgy Flyorov, Russian physicist
115	Mc	Moscovium	Moscow Oblast, Russia, where the element was first synthesised
116	Lv	Livermorium	Lawrence Livermore National Laboratory in Livermore, California, which collaborated with JINR on its synthesis
117	Ts	Tennessine	Tennessee, United States
118	Og	Oganesson	Yuri Oganessian, Russian physicist

Symbols and names not currently used

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

Some older systematic names and symbols, used for elements 101 to 118, are no longer in use. They have been replaced by trivial (non-systematic) names and symbols, such as mendelevium, nobelium, lawrencium, rutherfordium, dubnium, seaborgium, bohrium, hassium, meitnerium, darmstadtium, roentgenium, copernicium, nihonium, flerovium, moscovium, livermorium, tennessine, and oganesson. When elements beyond oganesson, starting with ununennium (Uue, element 119), are discovered, their systematic names and symbols will presumably be replaced by trivial names and symbols too.

Main article: Alchemical symbols

The ideographic symbols used in alchemy to show elements known since ancient times were not the only ones. Many more symbols were in at least sporadic use, and one early 17th-century alchemical manuscript lists 22 symbols for mercury alone. Spurious elements, such as the classical elements fire and water or phlogiston, were not included. Alchemists often used the names of the seven planets for the seven metals known since Classical times. These planetary metals were linked together until antimony, bismuth and zinc were discovered in the 16th century. Alchemists would typically call metals by planetary names, such as "Saturn" for lead and "Mars" for iron. The tradition remains in the name of the element mercury and in a few old terms, such as lunar caustic (silver nitrate) and saturnism (lead poisoning).

Daltonian symbols

The following symbols were used by John Dalton in the early 1800s, as the periodic table of elements was being formulated. Symbols for compounds, such as certain rare-earth mineral blends, were not included. Modern alphabetic notation was introduced in 1814 by Jöns Jakob Berzelius. Its early form can be seen in Dalton's circled letters for 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.

Symbol	Name	Atomic number
A	Argon	18
Ab	Alabamine	85
Ad	Aldebaranium	70
Ah	Anglohelvetium	85
Ak	Alkalinium	87
Am	Alabamine	85
An	Athenium	99
Ao	Ausonium	93
At	Austriacum	84
Az	Azote	7
Bo	Bohemium	93
Bo	Boron	5
Bv	Brevium	91
Bz	Berzelium	90
Cb	Columbium	41
Ch	Chromium	24
Cl	Columbium	41
Cm	Catium	87
Cn	Carolinium	90
Cp	Cassiopeium	71
Cp	Copernicium	112
Ct	Celtium	72
Ct	Centurium	100
Cy	Cyclonium	61
D	Didymium	59/60
Da	Davyum	43
Db	Dubhium	69
Db	Dubnium	104
Dc	Decipium	62
Dc	Dvicaesium	87
De	Denebium	69
Di	Didymium	59/60
Do	Dor	85
Dn	Dubnadium	118
Dp	Decipium	62
Ds	Dysprosium	66
Dt	Dvitellurium	84
E	Einsteinium	99
E	Erbium	68
Ea	Ekaaluminium	31
Eb	Ekaboron	21
Eb	Erebodium	42
El	Ekaaluminium	31
Em	Ekamanganese	43
Em	Emanation	86
Em	Emanium	89
Es	Ekasilicon	32
Hs	Hesperium	94
Et	Ekatantalum	91
Ex	Euxenium	72
Fa	Francium	87
Fl	Florentium	61
Fl	Fluorine	9
Fr	Florentium	61
G	Glucinium	4
Gh	Ghiorsium	118
Gl	Glucinium	4
Ha	Hahnium	105
Hn	Hahnium	108
Hv	Helvetium	85
Hy	Mercury	80
I	Iridium	77
Ic	Incognitium	65
Il	Illinium	61
Il	Ilmenium	41/73
Io	Ionium	65
J	Jodium	53
Jg	Jargonium	72
Jl	Joliotium	105
Jp	Japonium	113
Ka	Potassium	19
Ku	Kurchatovium	104
L	Lithium	3
Lw	Lawrencium	103
M	Muriaticum	17
Ma	Manganese	25
Ma	Masurium	43
Md	Mendelevium	97
Ml	Moldavium	87
Ms	Magnesium	12
Ms	Masrium	88
Ms	Masurium	43
Ms	Mosandrium	65
Mv	Mendelevium	101
Ng	Norwegium	72
No	Norium	72
Np	Neptunium	91
Np	Nipponium	43
Ns	Nielsbohrium	105
Ns	Nielsbohrium	107
Nt	Niton	86
Ny	Neoytterbium	70
P	Lead	82
Pa	Palladium	46
Pe	Pelopium	41
Ph	Phosphorus	15
Pl	Palladium	46
Pm	Polymnestum	33
Po	Potassium	19
Pp	Philippium	67
R	Rhodium	45
Rd	Radium	88
Rf	Rutherfordium	106
Ro	Rhodium	45
Sa	Samarium	62
So	Sodium	11
Sq	Sequanium	93
St	Antimony	51
St	Tin	50
Tm	Trimanganese	75
Tn	Tungsten	74
Tr	Terbium	65
Tu	Thulium	69
Tu	Tungsten	74
Ur	Uralium	75
Ur	Uranium	92
Vc	Victorium	64
Vi	Victorium	64
Vi	Virginium	87
Vm	Virginium	87
Va	Vanadium	23
Wo	Wolfram	74
X	Xenon	54
Yt	Yttrium	39

Alchemical symbols for the modern elements
	Element	Atomic number
	Phosphorus	15
🜍	Sulfur	16
	Manganese	25
♂	Iron	26
🜶	Cobalt	27
	Nickel	28
	Zinc	30
♀	Copper	29
🜺	Arsenic	33
☾	Silver	47
🜛	Silver	47
♃	Tin	50
♁	Antimony	51
	Platinum	78
⛢	Platinum	78
🜚	Gold	79
☉	Gold	79
☿	Mercury	80
♄	Lead	82
♆	Bismuth	83
♉︎	Bismuth	83

Daltonian symbols for the elements
Symbol		Dalton's name	Modern name	Atomic number
img.	char.	Dalton's name	Modern name	Atomic number
	☉	hydrogen		1
		glucine	beryllium	4
	●	carbone, carbon	carbon	6
	⦶	azote	nitrogen/azote	7
	○	oxygen		8
	⦷	soda	sodium	11
	⊛	magnesia	magnesium	12
		alumine	aluminium	13
	🟕	silex	silicon	14
		phosphorus		15
	🜨	sulphur		16
		potash	potassium	19
	⦾	lime	calcium	20
		titanium		22
		manganese		25
	Ⓘ	iron		26
	Ⓝ	nickel		28
		cobalt		27
	Ⓒ	copper		29
	Ⓩ	zinc		30
		arsenic		33
		strontian	strontium	38
	⊕︀︀	yttria	yttrium	39
		zircone	zirconium	40
	Ⓢ	silver		47
	Ⓣ	tin		50
		antimony		51
		barytes	barium	56
		cerium		58
		tungsten		74
	Ⓟ	platina	platinum	78
	Ⓖ	gold		79
		mercury		80
	Ⓛ	lead		82
	Ⓑ	bismuth		83
	Ⓤ	uranium		92

Symbols for named isotopes

This is a list of isotopes that have been given their own special symbols. It is not a list of today's standard symbols, which are written in the ^uAtom form. Those can be found elsewhere. The symbols for isotopes of hydrogen, deuterium (D) and tritium (T), are still used today, and so is thoron (Tn) for radon-220. The symbol actinon is not used, and people usually refer to a general actinide instead.

Chemists often use heavy water and other deuterated solvents. In these cases, it is simpler to use one letter than a symbol with a superscript, such as D₂O instead of ²H₂O. This practice also continues with tritium compounds. When the name of the solvent is given, a small d is sometimes used, so d₆-benzene or C₆D₆ can be written instead of C₆[²H₆]. Symbols for isotopes of other elements, apart from hydrogen and radon, are no longer used by scientists. Many of these were created in the early years of radiochemistry. Several isotopes, namely those in the decay chains of actinium, radium, and thorium, have placeholder names from an 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 ²²⁷Ac, 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 ²¹⁵Po, 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 ²¹¹Pb, 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 ²¹¹Bi, 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 ²¹¹Po, 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 its own character, usually made for that purpose (see Chemical elements in East Asian languages). Chinese also uses Latin letter symbols, especially in formulas. Chemists also use short letters for groups of things. For example, M means any metal, X means any halogen, and R means an unspecified part of a molecule that is not important to the discussion. Other letters stand for a ligand, a lanthanide, an actinide, a noble gas, a nucleophile, or an electrophile. The letter A can mean an anion, and B can mean a base.

Short symbols are also used in organic chemistry for parts of molecules. Examples include butyl, phenyl, benzyl, propyl, allyl, vinyl, and alkyl groups. Some symbols name more specific parts, such as adamantyl, mesityl, trityl, tosyl, and ferrocenyl. A few symbols also describe exotic atoms, such as muonium, protonium, and positronium.