IUPAC Commission on Isotopic Abundances and Atomic Weights.

ATOMIC WEIGHTS OF THE ELEMENTS 2013

These tables are based on the 2011 table at Pure Appl. Chem., 2013, 85, 1047-1078 with changes from for the values of aluminium, arsenic, beryllium, cadmium, caesium, cobalt, fluorine, gold, holmium, manganese, molybdenum, niobium, phosphorus, praseodymium, scandium, selenium, thorium, thulium and yttrium [see ciaaw or IUPAC website or Chem. Int. 2013, 35(6), 17-18].

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

A PDF format copy (1647 KBt) of the 2011 table is available from the abstract

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

Previous values may be consulted from the 1993 table, the 1995 table, the 1997 table, the 1999 table, the 2001 table, the 2005 table, the 2007 table, the 2009 table or the 2011 table.

The standard atomic weights of twelve elements having two or more stable isotopes have variability of atomic-weight values in natural terrestrial materials. These are given in table 1 below. In the other lists the values quoted are those suggested for material where the origin of the sample is unknown. For radioactive elements the isotope with the longest half-life is quoted in parenthesis. The original paper should be consulted for full details of the variation in atomic weight and the half life of the radioisotopes quoted below.

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

See below for the elements listed in Atomic Number Order or Name order.

See also a copy of the periodic table with atomic weights to five significant figures.

Table 1. List of Elements with Range of Atomic Weights.

At No     Symbol     Name                 Minimum Atomic Wt     Maximum Atomic Wt
1Hhydrogen    1.007 84    1.008 11
3Lilithium    6.938    6.997
5Bboron  10.806  10.821
6Ccarbon  12.0096  12.0116
7Nnitrogen  14.006 43  14.007 28
8Ooxygen  15.999 03  15.999 77
12Mgmagnesium  24.30  24.31
14Sisilicon  28.084  28.086
16Ssulfur  32.059  32.076
17Clchlorine  35.446  35.457
35Brbromine  79.90  79.91
81Tlthallium204.382204.385

See original paper for the range of these elements from different sources.

Table 2. List of Elements in Atomic Number Order.

At No     Symbol     NameAtomic WtNotes
1HHydrogen1.0083, 6
2HeHelium4.002602(2)1, 2
3LiLithium6.943, 6
4BeBeryllium9.0121831(5)
5BBoron10.813, 6
6CCarbon12.0116
7NNitrogen14.0076
8OOxygen15.9996
9FFluorine18.998403163(6)
10NeNeon20.1797(6)1, 3
11NaSodium22.98976928(2)    
12MgMagnesium24.3056
13AlAluminium26.9815385(7)
14SiSilicon28.0856
15PPhosphorus30.973761998(5)
16SSulfur32.066
17ClChlorine35.453, 6
18ArArgon39.948(1)1, 2
19KPotassium39.0983(1)
20CaCalcium40.078(4)
21ScScandium44.955908(5)
22TiTitanium47.867(1)
23VVanadium50.9415(1)
24CrChromium51.9961(6)
25MnManganese54.938044(3)
26FeIron55.845(2)
27CoCobalt58.933194(4)
28NiNickel58.6934(4)2
29CuCopper63.546(3)2
30ZnZinc65.38(2)2
31GaGallium69.723(1)
32GeGermanium72.630(8)
33AsArsenic74.921595(6)
34SeSelenium78.971(8)
35BrBromine79.9046
36KrKrypton83.798(2)1, 3
37RbRubidium85.4678(3)1
38SrStrontium87.62(1)1, 2
39YYttrium88.90584(2)
40ZrZirconium91.224(2)1
41NbNiobium92.90637(2)
42MoMolybdenum95.95(1)1
43TcTechnetium[97]4
44RuRuthenium101.07(2)1
45RhRhodium102.90550(2)
46PdPalladium106.42(1)1
47AgSilver107.8682(2)1
48CdCadmium112.414(4)1
49InIndium114.818(1)
50SnTin118.710(7)1
51SbAntimony121.760(1)1
52TeTellurium127.60(3)1
53IIodine126.90447(3)
54XeXenon131.293(6)1, 3
55CsCaesium132.90545196(6)
56BaBarium137.327(7)
57LaLanthanum138.90547(7)1
58CeCerium140.116(1)1
59PrPraseodymium     140.90766(2)
60NdNeodymium144.242(3)1
61PmPromethium[145]5
62SmSamarium150.36(2)1
63EuEuropium151.964(1)1
64GdGadolinium157.25(3)1
65TbTerbium158.92535(2)
66DyDysprosium162.500(1)1
67HoHolmium164.93033(2)
68ErErbium167.259(3)1
69TmThulium168.93422(2)
70YbYtterbium173.054(5)1
71LuLutetium174.9668(1)1
72HfHafnium178.49(2)
73TaTantalum180.94788(2)
74WTungsten183.84(1)
75ReRhenium186.207(1)
76OsOsmium190.23(3)1
77IrIridium192.217(3)
78PtPlatinum195.084(9)
79AuGold196.966569(5)
80HgMercury200.592(3)
81TlThallium204.386
82PbLead207.2(1)1, 2
83BiBismuth208.98040(1)
84PoPolonium[209]4
85AtAstatine[210]4
86RnRadon[222]4
87FrFrancium[223]4
88RaRadium[226]4
89AcActinium[227]4
90ThThorium232.0377(4)1, 4
91PaProtactinium231.03588(2)4
92UUranium238.02891(3)1, 3, 4
93NpNeptunium[237]4
94PuPlutonium[244]4
95AmAmericium[243]4
96CmCurium[247]4
97BkBerkelium[247]4
98CfCalifornium[251]4
99EsEinsteinium[252]4
100FmFermium[257]4
101MdMendelevium[258]4
102NoNobelium[259]4
103LrLawrencium[262]4
104RfRutherfordium[267]4
105DbDubnium[270]4
106SgSeaborgium[271]4
107BhBohrium[270]4
108HsHassium[277]4
109MtMeitnerium[276]4
110DsDarmstadtium[281]4
111RgRoentgenium [282]4
112CnCopernicium[285]4
113UutUnuntrium [285]4, 5
114FlFlerovium[289]4, 5
115UupUnunpentium[2889]4, 5
116LvLivermorium[293]4, 5
117UusUnunseptium[294]4, 5
118UuoUnunoctium[294]4, 5

  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. 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.
  5. The names and symbols for elements 113, 115, 117 and 118 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 1979, 51, 381-384 is used above.
  6. See table 1 for details of range and original paper for the atomic weight of the element from different sources.

Table 3. List of Elements in Name Order.

At No     Symbol     NameAtomic WtNotes
89AcActinium[227]4
13AlAluminium26.9815385(7)
95AmAmericium[243]4
51SbAntimony121.760(1)1
18ArArgon39.948(1)1, 2
33AsArsenic74.921595(6)
85AtAstatine[210]4
56BaBarium137.327(7)
97BkBerkelium[247]4
4BeBeryllium9.0121831(5)
83BiBismuth208.98040(1)
107BhBohrium[270]4
5BBoron10.813, 6
35BrBromine79.9046
48CdCadmium112.414(4)1
55CsCaesium132.90545196(6)
20CaCalcium40.078(4)1
98CfCalifornium[251]4
6CCarbon12.0116
58CeCerium140.116(1)1
17ClChlorine35.453, 6
24CrChromium51.9961(6)
27CoCobalt58.933194(4)
112CnCopernicium[285]4
29CuCopper63.546(3)2
96CmCurium[247]4
110DsDarmstadtium[281]4
105DbDubnium[270]4
66DyDysprosium162.500(1)1
99EsEinsteinium[252]4
68ErErbium167.259(3)1
63EuEuropium151.964(1)1
100FmFermium[257]4
114FlFlerovium[289]4, 5
9FFluorine18.998403163(6)
87FrFrancium[223]4
64GdGadolinium157.25(3)1
31GaGallium69.723(1)
32GeGermanium72.630(8)
79AuGold196.966569(5)
72HfHafnium178.49(2)
108HsHassium[277]4
2HeHelium4.002602(2)1, 2
67HoHolmium164.93033(2)
1HHydrogen1.0083, 6
49InIndium114.818(1)
53IIodine126.90447(3)
77IrIridium192.217(3)
26FeIron55.845(2)
36KrKrypton83.798(2)1, 3
57LaLanthanum138.90547(7)1
103LrLawrencium[262]4
82PbLead207.2(1)1, 2
3LiLithium6.943, 6
116LvLivermorium[293]4, 5
71LuLutetium174.9668(1)1
12MgMagnesium24.3056
25MnManganese54.938044(3)
109MtMeitnerium[276]4
101MdMendelevium[258]4
80HgMercury200.592(3)
42MoMolybdenum95.95(1)1
60NdNeodymium144.242(3)1
10NeNeon20.1797(6)1, 3
93NpNeptunium[237]4
28NiNickel58.6934(4)
41NbNiobium92.90637(2)
7NNitrogen14.0076
102NoNobelium[259]4
76OsOsmium190.23(3)1
8OOxygen15.9996
46PdPalladium106.42(1)1
15PPhosphorus30.973761998(5)
78PtPlatinum195.084(9)
94PuPlutonium[244]4
84PoPolonium[209]4
19KPotassium39.0983(1)
59PrPraseodymium     140.90766(2)
61PmPromethium[145]4
91PaProtactinium231.03588(2)4
88RaRadium[226]4
86RnRadon[222]4
75ReRhenium186.207(1)
45RhRhodium102.90550(2)
111RgRoentgenium [282]4
37RbRubidium85.4678(3)1
44RuRuthenium101.07(2)1
104RfRutherfordium[267]4
62SmSamarium150.36(2)1
21ScScandium44.955908(5)
106SgSeaborgium[271]4
34SeSelenium78.971(8)
14SiSilicon28.0856
47AgSilver107.8682(2)1
11NaSodium22.98976928(2)    
38SrStrontium87.62(1)1, 2
16SSulfur32.066
73TaTantalum180.94788(2)
43TcTechnetium[97]4
52TeTellurium127.60(3)1
65TbTerbium158.92535(2)
81TlThallium204.386
90ThThorium232.0377(4)1, 4
69TmThulium168.93422(2)
50SnTin118.710(7)1
22TiTitanium47.867(1)
74WTungsten183.84(1)
118UuoUnunoctium[294]4, 5
115UupUnunpentium[289]4, 5
117UusUnunseptium[294]4, 5
113UutUnuntrium [285]4, 5
92UUranium238.02891(3)1, 3, 4
23VVanadium50.9415(1)
54XeXenon131.293(6)1, 3
70YbYtterbium173.054(5)1
39YYttrium88.90584(2)
30ZnZinc65.38(2)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. 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.
  5. The names and symbols for elements 113, 115, 117 and 118 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 1979, 51, 381-384 is used above.
  6. See table 1 for details of range and original paper for the atomic weight of the element from different sources.

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