IUPAC Commission on Atomic Weights and Isotopic Abundances.

ATOMIC WEIGHTS OF THE ELEMENTS 2007

These tables are based on the 2007 table at Pure Appl. Chem., 81, 2131-2156 (2009) with changes to the values for lutetium, molybdenum, nickel, ytterbium and zinc from the 2005 table. Mass number of the longest-lived isotope of hassium from Phys. Rev. Lett., 97 242501 (2006). For the name of element 112 see Pure Appl. Chem. 2010, 82, 753-755. A press release states that element 117 has been synthesised

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

A PDF of the 2007 table is available.

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 or the 2005 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
11NaSodium22.98976928(2)
12MgMagnesium24.3050(6)
13AlAluminium26.9815386(8)
14SiSilicon28.0855(3)2
15PPhosphorus30.973762(2)
16SSulfur32.065(5)1, 2
17ClChlorine35.453(2)3
18ArArgon39.948(1)1, 2
19KPotassium39.0983(1)1
20CaCalcium40.078(4)1
21ScScandium44.955912(6)
22TiTitanium47.867(1)
23VVanadium50.9415(1)
24CrChromium51.9961(6)
25MnManganese54.938045(5)
26FeIron55.845(2)
27CoCobalt58.933195(5)
28NiNickel58.6934(4)
29CuCopper63.546(3)2
30ZnZinc65.38(2)
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)
42MoMolybdenum95.96(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
55CsCaesium132.9054519(2)
56BaBarium137.327(7)
57LaLanthanum138.90547(7)1
58CeCerium140.116(1)1
59PrPraseodymium140.90765(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
67HoHolmium164.93032(2)
68ErErbium167.259(3)1
69TmThulium168.93421(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(4)
80HgMercury200.59(2)
81TlThallium204.3833(2)
82PbLead207.2(1)1, 2
83BiBismuth208.98040(1)
84PoPolonium[209]5
85AtAstatine[210]5
86RnRadon[222]5
87FrFrancium[223]5
88RaRadium[226]5
89AcActinium[227]5
90ThThorium232.03806(2)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[265]5
105DbDubnium[268]5
106SgSeaborgium[271]5
107BhBohrium[272]5
108HsHassium[270]5
109MtMeitnerium[276]5
110DsDarmstadtium[281]5
111RgRoentgenium [280]5
112CnCopernicium[285]5, 6
113UutUnuntrium [284]5, 6
114UuqUnunquadium[289]5, 6
115UupUnunpentium[288]5, 6
116UuhUnunhexium[293]5, 6
117UusUnunseptium5, 6
118UuoUnunoctium[294]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 6.939 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 113-118 are under review. 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
13AlAluminium26.9815386(8)
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)
83BiBismuth208.98040(1)
107BhBohrium[272]5
5BBoron10.811(7)1, 2, 3
35BrBromine79.904(1)
48CdCadmium112.411(8)1
55CsCaesium132.9054519(2)
20CaCalcium40.078(4)1
98CfCalifornium[251]5
6CCarbon12.0107(8)1, 2
58CeCerium140.116(1)1
17ClChlorine35.453(2)3
24CrChromium51.9961(6)
27CoCobalt58.933195(5)
112CnCopernicium[285]5, 6
29CuCopper63.546(3)2
96CmCurium[247]5
110DsDarmstadtium[281]5
105DbDubnium[268]5
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)
79AuGold196.966569(4)
72HfHafnium178.49(2)
108HsHassium[270]5
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
57LaLanthanum138.90547(7)1
103LrLawrencium[262]5
82PbLead207.2(1)1, 2
3LiLithium[6.941(2)]1, 2, 3, 4
71LuLutetium174.9668(1)1
12MgMagnesium24.3050(6)
25MnManganese54.938045(5)
109MtMeitnerium[276]5
101MdMendelevium[258]5
80HgMercury200.59(2)
42MoMolybdenum95.96(2)1
60NdNeodymium144.242(3)1
10NeNeon20.1797(6)1, 3
93NpNeptunium[237]5
28NiNickel58.6934(4)
41NbNiobium92.90638(2)
7NNitrogen14.0067(2)1, 2
102NoNobelium[259]5
76OsOsmium190.23(3)1
8OOxygen15.9994(3)1, 2
46PdPalladium106.42(1)1
15PPhosphorus30.973762(2)
78PtPlatinum195.084(9)
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 [280]5
37RbRubidium85.4678(3)1
44RuRuthenium101.07(2)1
104RfRutherfordium[265]5
62SmSamarium150.36(2)1
21ScScandium44.955912(6)
106SgSeaborgium[271]5
34SeSelenium78.96(3)
14SiSilicon28.0855(3)2
47AgSilver107.8682(2)1
11NaSodium22.98976928(2)
38SrStrontium87.62(1)1, 2
16SSulfur32.065(5)1, 2
73TaTantalum180.94788(2)
43TcTechnetium[98]5
52TeTellurium127.60(3)1
65TbTerbium158.92535(2)
81TlThallium204.3833(2)
90ThThorium232.03806(2)1, 5
69TmThulium168.93421(2)
50SnTin118.710(7)1
22TiTitanium47.867(1)
74WTungsten183.84(1)
116UuhUnunhexium[293]5, 6
118UuoUnunoctium[294]5, 6
115UupUnunpentium[288]5, 6
114UuqUnunquadium[289]5, 6
117UusUnunseptium5, 6
113UutUnuntrium [284]5, 6
92UUranium238.02891(3)1, 3, 5
23VVanadium50.9415(1)
54XeXenon131.293(6)1, 3
70YbYtterbium173.054(5)1
39YYttrium88.90585(2)
30ZnZinc65.38(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 6.939 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 113-118 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above.

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