ATOMIC WEIGHTS OF THE ELEMENTS 1993

IUPAC Commission on Atomic Weights and Isotopic Abundances.

Pure Appl. Chem., 66, 2423-2444 (1994)

World Wide Web version of atomic weight data prepared by G. P. Moss from a file provided by D. R. Lide.

This revision of the 1991 table has resulted in changes in the standard values for Ti, Fe, Sb and Ir. Recent investigations on Cl and Br confirm the accepted values. See also the 2001 table for more recent values.

The original paper should be consulted for details of the half life of the radioisotopes quoted below. In addition there are recommendations on the scales for quoting relative isotope-ratio data for stable hydrogen, carbon and oxygen. Also there is a report on the different isotopic compositions of some non-terrestrial materials.

A number in parentheses indicates the uncertainty in the last digit of the atomic weight.

See also below the list in Name order.

List of Elements in Atomic Number Order.

At NoSymbolNameAtomic WtNotes
1HHydrogen1.00794(7)1, 2, 3
2HeHelium4.002602(2)1, 2
3LiLithium6.941(2)1, 2, 3, 4
4BeBeryllium9.012182(3)
5BBoron10.811(5)1, 2, 3
6CCarbon12.011(1)1, 2
7NNitrogen14.00674(7)1, 2
8OOxygen15.9994(3)1, 2
9FFluorine18.9984032(9)
10NeNeon20.1797(6)1, 3
11NaSodium22.989768(6)
12MgMagnesium24.3050(6)
13AlAluminium26.981539(5)
14SiSilicon28.0855(3)2
15PPhosphorus30.973762(4)
16SSulfur32.066(6)1, 2
17ClChlorine35.4527(9)3
18ArArgon39.948(1)1, 2
19KPotassium39.0983(1)1
20CaCalcium40.078(4)1
21ScScandium44.955910(9)
22TiTitanium47.867(1)
23VVanadium50.9415(1)
24CrChromium51.9961(6)
25MnManganese54.93805(1)
26FeIron55.845(2)
27CoCobalt58.93320(1)
28NiNickel58.6934(2)
29CuCopper63.546(3)2
30ZnZinc65.39(2)
31GaGallium69.723(1)
32GeGermanium72.61(2)
33AsArsenic74.92159(2)
34SeSelenium78.96(3)
35BrBromine79.904(1)
36KrKrypton83.80(1)1, 3
37RbRubidium85.4678(3)1
38SrStrontium87.62(1)1, 2
39YYttrium88.90585(2)
40ZrZirconium91.224(2)1
41NbNiobium92.90638(2)
42MoMolybdenum95.94(1)1
43TcTechnetium[98]5
44RuRuthenium101.07(2)1
45RhRhodium102.90550(3)
46PdPalladium106.42(1)1
47AgSilver107.8682(2)1
48CdCadmium112.411(8)1
49InIndium114.818(3)
50SnTin118.710(7)1
51SbAntimony121.760(1)1
52TeTellurium127.60(3)1
53IIodine126.90447(3)
54XeXenon131.29(2)1, 3
55CsCaesium132.90543(5)
56BaBarium137.327(7)
57LaLanthanum138.9055(2)1
58CeCerium140.115(4)1
59PrPraseodymium140.90765(3)
60NdNeodymium144.24(3)1
61PmPromethium[145]5
62SmSamarium150.36(3)1
63EuEuropium151.965(9)1
64GdGadolinium157.25(3)1
65TbTerbium158.92534(3)
66DyDysprosium162.50(3)1
67HoHolmium164.93032(3)
68ErErbium167.26(3)1
69TmThulium168.93421(3)
70YbYtterbium173.04(3)1
71LuLutetium174.967(1)1
72HfHafnium178.49(2)
73TaTantalum180.9479(1)
74WTungsten183.84(1)
75ReRhenium186.207(1)
76OsOsmium190.23(3)1
77IrIridium192.217(3)
78PtPlatinum195.08(3)
79AuGold196.96654(3)
80HgMercury200.59(2)
81TlThallium204.3833(2)
82PbLead207.2(1)1, 2
83BiBismuth208.98037(3)
84PoPolonium[209]5
85AtAstatine[210]5
86RnRadon[222]5
87FrFrancium[223]5
88RaRadium[226]5
89AcActinium[227]5
90ThThorium232.0381(1)1, 5
91PaProtactinium231.03588(2)5
92UUranium238.0289(1)1, 3, 5
93NpNeptunium[237]5
94PuPlutonium[244]5
95AmAmericium[243]5
96CmCurium[247]5
97BkBerkelium[247]5
98CfCalifornium[251]5
99EsEinsteinium[252]5
100FmFermium[257]5
101MdMendelevium[258]5
102NoNobelium[259]5
103LrLawrencium[262]5
104UnqUnnilquadium[261]5, 6
105UnpUnnilpentium[262]5, 6
106UnhUnnilhexium[263]5, 6
107UnsUnnilseptium[262]5, 6
108UnoUnniloctium[265]5, 6
109UneUnnilennium[266]5, 6

  1. Geological specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the Table may exceed the stated uncertainty.
  2. Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
  3. Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertant isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
  4. Commercially available Li materials have atomic weights that range between 6.94 and 6.99; if a more accurate value is required, it must be determined for the specific material.
  5. Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
  6. The names and symbols for elements 104-109 are under review. Proposals have been published in Pure Appl. Chem., 66, 2419-2421 (1994) but these are not definitive and may change [See back inside cover of Pure Appl. Chem., 68 (1996) issues 1, 2, 4 and 5]. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above.

List of Elements in Name Order.

At NoSymbolNameAtomic WtNotes
89AcActinium[227]5
13AlAluminium26.981539(5)
95AmAmericium[243]5
51SbAntimony121.760(1)1
18ArArgon39.948(1)1, 2
33AsArsenic74.92159(2)
85AtAstatine[210]5
56BaBarium137.327(7)
97BkBerkelium[247]5
4BeBeryllium9.012182(3)
83BiBismuth208.98037(3)
5BBoron10.811(5)1, 2, 3
35BrBromine79.904(1)
48CdCadmium112.411(8)1
55CsCaesium132.90543(5)
20CaCalcium40.078(4)1
98CfCalifornium[251]5
6CCarbon12.011(1)1, 2
58CeCerium140.115(4)1
17ClChlorine35.4527(9)3
24CrChromium51.9961(6)
27CoCobalt58.93320(1)
29CuCopper63.546(3)2
96CmCurium[247]5
66DyDysprosium162.50(3)1
99EsEinsteinium[252]5
68ErErbium167.26(3)1
63EuEuropium151.965(9)1
100FmFermium[257]5
9FFluorine18.9984032(9)
87FrFrancium[223]5
64GdGadolinium157.25(3)1
31GaGallium69.723(1)
32GeGermanium72.61(2)
79AuGold196.96654(3)
72HfHafnium178.49(2)
2HeHelium4.002602(2)1, 2
67HoHolmium164.93032(3)
1HHydrogen1.00794(7)1, 2, 3
49InIndium114.818(3)
53IIodine126.90447(3)
77IrIridium192.217(3)
26FeIron55.845(2)
36KrKrypton83.80(1)1, 3
57LaLanthanum138.9055(2)1
103LrLawrencium[262]5
82PbLead207.2(1)1, 2
3LiLithium6.941(2)1, 2, 3, 4
71LuLutetium174.967(1)1
12MgMagnesium24.3050(6)
25MnManganese54.93805(1)
101MdMendelevium[258]5
80HgMercury200.59(2)
42MoMolybdenum95.94(1)1
60NdNeodymium144.24(3)1
10NeNeon20.1797(6)1, 3
93NpNeptunium[237]5
28NiNickel58.6934(2)
41NbNiobium92.90638(2)
7NNitrogen14.00674(7)1, 2
102NoNobelium[259]5
76OsOsmium190.23(3)1
8OOxygen15.9994(3)1, 2
46PdPalladium106.42(1)1
15PPhosphorus30.973762(4)
78PtPlatinum195.08(3)
94PuPlutonium[244]5
84PoPolonium[209]5
19KPotassium39.0983(1)1
59PrPraseodymium140.90765(3)
61PmPromethium[145]5
91PaProtactinium231.03588(2)5
88RaRadium[226]5
86RnRadon[222]5
75ReRhenium186.207(1)
45RhRhodium102.90550(3)
37RbRubidium85.4678(3)1
44RuRuthenium101.07(2)1
62SmSamarium150.36(3)1
21ScScandium44.955910(9)
34SeSelenium78.96(3)
14SiSilicon28.0855(3)2
47AgSilver107.8682(2)1
11NaSodium22.989768(6)
38SrStrontium87.62(1)1, 2
16SSulfur32.066(6)1, 2
73TaTantalum180.9479(1)
43TcTechnetium[98]5
52TeTellurium127.60(3)1
65TbTerbium158.92534(3)
81TlThallium204.3833(2)
90ThThorium232.0381(1)1, 5
69TmThulium168.93421(3)
50SnTin118.710(7)1
22TiTitanium47.867(1)
74WTungsten183.84(1)
109UneUnnilennium[266]5, 6
106UnhUnnilhexium[263]5, 6
108UnoUnniloctium[265]5, 6
105UnpUnnilpentium[262]5, 6
104UnqUnnilquadium[261]5, 6
107UnsUnnilseptium[262]5, 6
92UUranium238.0289(1)1, 3, 5
23VVanadium50.9415(1)
54XeXenon131.29(2)1, 3
70YbYtterbium173.04(3)1
39YYttrium88.90585(2)
30ZnZinc65.39(2)
40ZrZirconium91.224(2)1

  1. Geological specimens are known in which the element has an isotopic composition outside the limits for normal material. The difference between the atomic weight of the element in such specimens and that given in the Table may exceed the stated uncertainty.
  2. Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
  3. Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertant isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
  4. Commercially available Li materials have atomic weights that range between 6.94 and 6.99; if a more accurate value is required, it must be determined for the specific material.
  5. Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
  6. The names and symbols for elements 104-109 are under review. Proposals have been published in Pure Appl. Chem., 66, 2419-2421 (1994) but these are not definitive and may change [See back inside cover of Pure Appl. Chem., 68 (1996) issues 1, 2, 4 and 5]. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above.

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