IUPAC Commission on Atomic Weights and Isotopic Abundances.

ATOMIC WEIGHTS OF THE ELEMENTS 2001

Values from the 2001 table Pure Appl. Chem., 75, 1107-1122 (2003). A PDF of the printed version is available. The values of zinc, krypton, molybdenum and dysprosium have been modified. The approved name for element 110 is included, see Pure Appl. Chem., 75, 1613-1615 (2003). The approved name for element 111 is also included, see Pure Appl. Chem., 76, 2101-2103 (2004).

http://www.chem.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 Lett. 1999, 83, 1104] for elements 116 and 118 has been withdrawn [see Chem.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); 2002, 80, 12 (22 July 2002);Phys. Rev. Lett. 2002, 89, 039901]

Previous values may be consulted from the 1993 table, the 1995 table, the 1997 table or the 1999 table.

The original paper should be consulted for details of the half life of the radioisotopes quoted below. 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
30ZnZinc65.409(4)
31GaGallium69.723(1)
32GeGermanium72.64(1)
33AsArsenic74.92160(2)
34SeSelenium78.96(3)
35BrBromine79.904(1)
36KrKrypton83.798(2)1, 3
37RbRubidium85.4678(3)1
38SrStrontium87.62(1)1, 2
39YYttrium88.90585(2)
40ZrZirconium91.224(2)1
41NbNiobium92.90638(2)
42MoMolybdenum95.94(2)1
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)
66DyDysprosium162.500(1)1
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
110DsDarmstadtium[281]5, 6
111RgRoentgenium [272]5, 6
112UubUnunbium[285]5, 6
113UutUnuntrium [284]5, 7
114UuqUnunquadium[289]5, 6
115UupUnunpentium[288]5, 7
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 112-118 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),for element 110 in 2003 (see Pure Appl. Chem., 2003, 75, 1613-1615) and for element 111 in 2004 (see Pure Appl. Chem., 2004, 76, 2101-2103).
  7. A report in Phys. Rev. C, 2004, 69, 021601 (R) claims the detection of elements 113 and 115.

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
110DsDarmstadtium[281]5, 6
105DbDubnium[262]5, 6
66DyDysprosium162.500(1)1
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)
36KrKrypton83.798(2)1, 3
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(2)1
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)
111RgRoentgenium [272]5, 6
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
118UuoUnunoctiumsee Note above
115UupUnunpentium[288]5, 7
114UuqUnunquadium[289]5, 6
113UutUnuntrium [284]5, 7
92UUranium238.02891(3)1, 3, 5
23VVanadium50.9415(1)
54XeXenon131.293(6)1, 3
70YbYtterbium173.04(3)1
39YYttrium88.90585(2)
30ZnZinc65.409(4)
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 112-118 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),for element 110 in 2003 (see Pure Appl. Chem., 2003, 75, 1613-1615) and for element 111 in 2004 (see Pure Appl. Chem., 2004, 76, 2101-2103).
  7. A report in Phys. Rev. C, 2004, 69, 021601 (R) claims the detection of elements 113 and 115.

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