IUPAC Commission on Isotopic Abundances and Atomic Weights.

ATOMIC WEIGHTS OF THE ELEMENTS 2015

These tables are based on the 2013 table at Pure Appl. Chem., 2016, 88, 265-291 with changes from the 2011 table for the values of aluminium, arsenic, beryllium, cadmium, caesium, cobalt, fluorine, gold, holmium, manganese, molybdenum, niobium, phosphorus, praseodymium, scandium, selenium, thorium, thulium and yttrium. For the 2015 table the atomic weight of ytterbium has been revised [see ciaaw or Chem. Eng. News, 2015, 93(37), 9].

The discovery of elements 113, 115, 117 and 118 have been verified by IUPAC. See Pure Appl. Chem., 2016, 88, 139-153 for elements 113, 115 and 117 and Pure Appl. Chem., 2016, 88, 155-160 for element 118. Their proposed names are nihonium (Nh), moscovium (Mc), tennessine (Ts) and oganesson (Og) IUPAC News Announcement.

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

A PDF format copy (2.7 MBt) of the 2013 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, the 2011 table or the 2013 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  24.304  24.307
14Sisilicon  28.084  28.086
16Ssulfur  32.059  32.076
17Clchlorine  35.446  35.457
35Brbromine  79.901  79.907
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, 5
2HeHelium4.002 602(2)1, 2
3LiLithium6.943, 5
4BeBeryllium9.012 1831(5)
5BBoron10.813, 5
6CCarbon12.0115
7NNitrogen14.0075
8OOxygen15.9995
9FFluorine18.998 403 163(6)
10NeNeon20.1797(6)1, 3
11NaSodium22.989 769 28(2)    
12MgMagnesium24.3055
13AlAluminium26.981 5385(7)
14SiSilicon28.0855
15PPhosphorus30.973 761 998(5)
16SSulfur32.065
17ClChlorine35.453, 5
18ArArgon39.948(1)1, 2
19KPotassium39.0983(1)
20CaCalcium40.078(4)
21ScScandium44.955 908(5)
22TiTitanium47.867(1)
23VVanadium50.9415(1)
24CrChromium51.9961(6)
25MnManganese54.938 044(3)
26FeIron55.845(2)
27CoCobalt58.933 194(4)
28NiNickel58.6934(4)2
29CuCopper63.546(3)2
30ZnZinc65.38(2)2
31GaGallium69.723(1)
32GeGermanium72.630(8)
33AsArsenic74.921 595(6)
34SeSelenium78.971(8)
35BrBromine79.9045
36KrKrypton83.798(2)1, 3
37RbRubidium85.4678(3)1
38SrStrontium87.62(1)1, 2
39YYttrium88.905 84(2)
40ZrZirconium91.224(2)1
41NbNiobium92.906 37(2)
42MoMolybdenum95.95(1)1
43TcTechnetium[97]4
44RuRuthenium101.07(2)1
45RhRhodium102.905 50(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
53IIodine126.904 47(3)
54XeXenon131.293(6)1, 3
55CsCaesium132.905 451 96(6)
56BaBarium137.327(7)
57LaLanthanum138.905 47(7)1
58CeCerium140.116(1)1
59PrPraseodymium     140.907 66(2)
60NdNeodymium144.242(3)1
61PmPromethium[145]
62SmSamarium150.36(2)1
63EuEuropium151.964(1)1
64GdGadolinium157.25(3)1
65TbTerbium158.925 35(2)
66DyDysprosium162.500(1)1
67HoHolmium164.930 33(2)
68ErErbium167.259(3)1
69TmThulium168.934 22(2)
70YbYtterbium173.045(10)1
71LuLutetium174.9668(1)1
72HfHafnium178.49(2)
73TaTantalum180.947 88(2)
74WTungsten183.84(1)
75ReRhenium186.207(1)
76OsOsmium190.23(3)1
77IrIridium192.217(3)
78PtPlatinum195.084(9)
79AuGold196.966 569(5)
80HgMercury200.592(3)
81TlThallium204.385
82PbLead207.2(1)1, 2
83BiBismuth208.980 40(1)
84PoPolonium[209]4
85AtAstatine[210]4
86RnRadon[222]4
87FrFrancium[223]4
88RaRadium[226]4
89AcActinium[227]4
90ThThorium232.0377(4)1, 4
91PaProtactinium231.035 88(2)4
92UUranium238.028 91(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[269]4
107BhBohrium[270]4
108HsHassium[270]4
109MtMeitnerium[278]4
110DsDarmstadtium[281]4
111RgRoentgenium [281]4
112CnCopernicium[285]4
113NhNihonium [286]4
114FlFlerovium[289]4
115McMoscovium[289]4
116LvLivermorium[293]4
117TsTennessine[293]4
118OgOganesson[294]4

  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. 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
13AlAluminium26.981 5385(7)
95AmAmericium[243]4
51SbAntimony121.760(1)1
18ArArgon39.948(1)1, 2
33AsArsenic74.921 595(6)
85AtAstatine[210]4
56BaBarium137.327(7)
97BkBerkelium[247]4
4BeBeryllium9.012 1831(5)
83BiBismuth208.980 40(1)
107BhBohrium[270]4
5BBoron10.813, 5
35BrBromine79.9045
48CdCadmium112.414(4)1
55CsCaesium132.905 451 96(6)
20CaCalcium40.078(4)1
98CfCalifornium[251]4
6CCarbon12.0115
58CeCerium140.116(1)1
17ClChlorine35.453, 5
24CrChromium51.9961(6)
27CoCobalt58.933 194(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
9FFluorine18.998 403 163(6)
87FrFrancium[223]4
64GdGadolinium157.25(3)1
31GaGallium69.723(1)
32GeGermanium72.630(8)
79AuGold196.966 569(5)
72HfHafnium178.49(2)
108HsHassium[270]4
2HeHelium4.002 602(2)1, 2
67HoHolmium164.930 33(2)
1HHydrogen1.0083, 5
49InIndium114.818(1)
53IIodine126.904 47(3)
77IrIridium192.217(3)
26FeIron55.845(2)
36KrKrypton83.798(2)1, 3
57LaLanthanum138.905 47(7)1
103LrLawrencium[262]4
82PbLead207.2(1)1, 2
3LiLithium6.943, 5
116LvLivermorium[293]4
71LuLutetium174.9668(1)1
12MgMagnesium24.3055
25MnManganese54.938 044(3)
109MtMeitnerium[278]4
101MdMendelevium[258]4
80HgMercury200.592(3)
42MoMolybdenum95.95(1)1
115McMoscovium[289]4
60NdNeodymium144.242(3)1
10NeNeon20.1797(6)1, 3
93NpNeptunium[237]4
28NiNickel58.6934(4)
113NhNihonium [286]4
41NbNiobium92.906 37(2)
7NNitrogen14.0075
102NoNobelium[259]4
118OgOganesson[294]4
76OsOsmium190.23(3)1
8OOxygen15.9995
46PdPalladium106.42(1)1
15PPhosphorus30.973 761 998(5)
78PtPlatinum195.084(9)
94PuPlutonium[244]4
84PoPolonium[209]4
19KPotassium39.0983(1)
59PrPraseodymium     140.907 66(2)
61PmPromethium[145]4
91PaProtactinium231.035 88(2)4
88RaRadium[226]4
86RnRadon[222]4
75ReRhenium186.207(1)
45RhRhodium102.905 50(2)
111RgRoentgenium [281]4
37RbRubidium85.4678(3)1
44RuRuthenium101.07(2)1
104RfRutherfordium[267]4
62SmSamarium150.36(2)1
21ScScandium44.955 908(5)
106SgSeaborgium[269]4
34SeSelenium78.971(8)
14SiSilicon28.0855
47AgSilver107.8682(2)1
11NaSodium22.989 769 28(2)    
38SrStrontium87.62(1)1, 2
16SSulfur32.065
73TaTantalum180.947 88(2)
43TcTechnetium[97]4
52TeTellurium127.60(3)1
117TsTennessine[293]4
65TbTerbium158.925 35(2)
81TlThallium204.385
90ThThorium232.0377(4)1, 4
69TmThulium168.934 22(2)
50SnTin118.710(7)1
22TiTitanium47.867(1)
74WTungsten183.84(1)
92UUranium238.028 91(3)1, 3, 4
23VVanadium50.9415(1)
54XeXenon131.293(6)1, 3
70YbYtterbium173.045(10)1
39YYttrium88.905 84(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. See table 1 for details of range and original paper for the atomic weight of the element from different sources.

Return to IUPAC Chemical Nomenclature home page