IUPAC Commission on Atomic Weights and Isotopic Abundances.

ATOMIC WEIGHTS OF THE ELEMENTS 1999

Pure Appl. Chem., 73, 667-683 (2001) The standard values and/or errors for nitrogen, sulfur, chlorine, germanium, xenon, erbium and uranium have been revised. Elements 114, 116 and 118 have been added (but see note below). The most stable radionuclide for seaborgium, hassium, elements 110 and 112 have been revised.

http://www.sbcs.qmul.ac.uk/iupac/AtWt/

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

Note The claim [Phys. Rev. Lett. 1999, 83, 1104] for elements 116 and 118 has been withdrawn [see Chem. Eng. News 2001, 79, 10 (6 August 2001); Phys. Rev. Lett. in press]

Previous values may be consulted from the 1993 table, the 1995 table or 1997 table

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, lithium, carbon, oxygen and sulfur. 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 a copy of the periodic table with atomic weights to five significant figures.

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
3LiLithium[6.941(2)]1, 2, 3, 4
4BeBeryllium9.012182(3)
5BBoron10.811(7)1, 2, 3
6CCarbon12.0107(8)1, 2
7NNitrogen14.0067(2)1, 2
8OOxygen15.9994(3)1, 2
9FFluorine18.9984032(5)
10NeNeon20.1797(6)1, 3
11NaSodium22.989770(2)
12MgMagnesium24.3050(6)
13AlAluminium26.981538(2)
14SiSilicon28.0855(3)2
15PPhosphorus30.973761(2)
16SSulfur32.065(5)1, 2
17ClChlorine35.453(2)3
18ArArgon39.948(1)1, 2
19KPotassium39.0983(1)1
20CaCalcium40.078(4)1
21ScScandium44.955910(8)
22TiTitanium47.867(1)
23VVanadium50.9415(1)
24CrChromium51.9961(6)
25MnManganese54.938049(9)
26FeIron55.845(2)
27CoCobalt58.933200(9)
28NiNickel58.6934(2)
29CuCopper63.546(3)2
30ZnZinc65.39(2)7
31GaGallium69.723(1)
32GeGermanium72.64(1)
33AsArsenic74.92160(2)
34SeSelenium78.96(3)
35BrBromine79.904(1)
36KrKrypton83.80(1)1, 3, 7
37RbRubidium85.4678(3)1
38SrStrontium87.62(1)1, 2
39YYttrium88.90585(2)
40ZrZirconium91.224(2)1
41NbNiobium92.90638(2)
42MoMolybdenum95.94(1)1, 7
43TcTechnetium[98]5
44RuRuthenium101.07(2)1
45RhRhodium102.90550(2)
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)
54XeXenon131.293(6)1, 3
55CsCaesium132.90545(2)
56BaBarium137.327(7)
57LaLanthanum138.9055(2)1
58CeCerium140.116(1)1
59PrPraseodymium140.90765(2)
60NdNeodymium144.24(3)1
61PmPromethium[145]5
62SmSamarium150.36(3)1
63EuEuropium151.964(1)1
64GdGadolinium157.25(3)1
65TbTerbium158.92534(2)
66DyDysprosium162.50(3)1, 7
67HoHolmium164.93032(2)
68ErErbium167.259(3)1
69TmThulium168.93421(2)
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)
78PtPlatinum195.078(2)
79AuGold196.96655(2)
80HgMercury200.59(2)
81TlThallium204.3833(2)
82PbLead207.2(1)1, 2
83BiBismuth208.98038(2)
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
92UUranium238.02891(3)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
104RfRutherfordium[261]5, 6
105DbDubnium[262]5, 6
106SgSeaborgium[266]5, 6
107BhBohrium[264]5, 6
108HsHassium[277]5, 6
109MtMeitnerium[268]5, 6
110UunUnunnilium[281]5, 6
111UuuUnununium[272]5, 6
112UubUnunbium[285]5, 6
114UuqUnunquadium[289]5, 6
116UuhUnunhexiumsee Note above
118UuoUnunoctiumsee Note above

  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 6.939 and 6.996; if a more accurate value is required, it must be determined for the specific material [range quoted for 1995 table 6.94 and 6.99].
  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 110-118 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above. The names of elements 101-109 were agreed in 1997 (See Pure Appl. Chem., 1997, 69, 2471-2473).
  7. The 2001 review agreed the following changes zinc 65.39(2) to 65.409(4), krypton 83.80(1) to 83.798(2), molybdenum 95.94(1) to 95.94(2) and dysprosium 162.50(3) to 162.500(1).

List of Elements in Name Order.

At NoSymbolNameAtomic WtNotes
89AcActinium[227]5
13AlAluminium26.981538(2)
95AmAmericium[243]5
51SbAntimony121.760(1)1
18ArArgon39.948(1)1, 2
33AsArsenic74.92160(2)
85AtAstatine[210]5
56BaBarium137.327(7)
97BkBerkelium[247]5
4BeBeryllium9.012182(3)
83BiBismuth208.98038(2)
107BhBohrium[264]5, 6
5BBoron10.811(7)1, 2, 3
35BrBromine79.904(1)
48CdCadmium112.411(8)1
55CsCaesium132.90545(2)
20CaCalcium40.078(4)1
98CfCalifornium[251]5
6CCarbon12.0107(8)1, 2
58CeCerium140.116(1)1
17ClChlorine35.453(2)3
24CrChromium51.9961(6)
27CoCobalt58.933200(9)
29CuCopper63.546(3)2
96CmCurium[247]5
105DbDubnium[262]5, 6
66DyDysprosium162.50(3)1, 7
99EsEinsteinium[252]5
68ErErbium167.259(3)1
63EuEuropium151.964(1)1
100FmFermium[257]5
9FFluorine18.9984032(5)
87FrFrancium[223]5
64GdGadolinium157.25(3)1
31GaGallium69.723(1)
32GeGermanium72.64(1)
79AuGold196.96655(2)
72HfHafnium178.49(2)
108HsHassium[277]5, 6
2HeHelium4.002602(2)1, 2
67HoHolmium164.93032(2)
1HHydrogen1.00794(7)1, 2, 3
49InIndium114.818(3)
53IIodine126.90447(3)
77IrIridium192.217(3)
26FeIron55.845(2)
36KrKrypton83.80(1)1, 3, 7
57LaLanthanum138.9055(2)1
103LrLawrencium[262]5
82PbLead207.2(1)1, 2
3LiLithium[6.941(2)]1, 2, 3, 4
71LuLutetium174.967(1)1
12MgMagnesium24.3050(6)
25MnManganese54.938049(9)
109MtMeitnerium[268]5, 6
101MdMendelevium[258]5
80HgMercury200.59(2)
42MoMolybdenum95.94(1)1, 7
60NdNeodymium144.24(3)1
10NeNeon20.1797(6)1, 3
93NpNeptunium[237]5
28NiNickel58.6934(2)
41NbNiobium92.90638(2)
7NNitrogen14.0067(2)1, 2
102NoNobelium[259]5
76OsOsmium190.23(3)1
8OOxygen15.9994(3)1, 2
46PdPalladium106.42(1)1
15PPhosphorus30.973761(2)
78PtPlatinum195.078(2)
94PuPlutonium[244]5
84PoPolonium[209]5
19KPotassium39.0983(1)1
59PrPraseodymium140.90765(2)
61PmPromethium[145]5
91PaProtactinium231.03588(2)5
88RaRadium[226]5
86RnRadon[222]5
75ReRhenium186.207(1)
45RhRhodium102.90550(2)
37RbRubidium85.4678(3)1
44RuRuthenium101.07(2)1
104RfRutherfordium[261]5, 6
62SmSamarium150.36(3)1
21ScScandium44.955910(8)
106SgSeaborgium[266]5, 6
34SeSelenium78.96(3)
14SiSilicon28.0855(3)2
47AgSilver107.8682(2)1
11NaSodium22.989770(2)
38SrStrontium87.62(1)1, 2
16SSulfur32.065(5)1, 2
73TaTantalum180.9479(1)
43TcTechnetium[98]5
52TeTellurium127.60(3)1
65TbTerbium158.92534(2)
81TlThallium204.3833(2)
90ThThorium232.0381(1)1, 5
69TmThulium168.93421(2)
50SnTin118.710(7)1
22TiTitanium47.867(1)
74WTungsten183.84(1)
112UubUnunbium[285]5, 6
116UuhUnunhexiumsee Note above
110UunUnunnilium[281]5, 6
118UuoUnunoctiumsee Note above
114UuqUnunquadium[289]5, 6
111UuuUnununium[272]5, 6
92UUranium238.02891(3)1, 3, 5
23VVanadium50.9415(1)
54XeXenon131.293(6)1, 3
70YbYtterbium173.04(3)1
39YYttrium88.90585(2)
30ZnZinc65.39(2)7
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 6.939 and 6.996; if a more accurate value is required, it must be determined for the specific material [range quoted for 1995 table 6.94 and 6.99].
  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 110-112 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above. The names of elements 101-109 were agreed in 1997 (See Pure Appl. Chem., 1997, 69, 2471-2473)
  7. The 2001 review agreed the following changes zinc 65.39(2) to 65.409(4), krypton 83.80(1) to 83.798(2), molybdenum 95.94(1) to 95.94(2) and dysprosium 162.50(3) to 162.500(1).

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