ATOMIC WEIGHTS OF THE ELEMENTS 1995

IUPAC Commission on Atomic Weights and Isotopic Abundances.

Pure Appl. Chem., 68, 2339-2359 (1996); 69, 2471-2473 (1997).

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

This revision of the 1993 table has resulted in changes in the standard values and/or error for B, C, F, Na, Al, P, Sc, Mn, Co, As, Rh, Cs, Ce, Pr, Eu, Tb, Ho, Tm, Pt, Au and Bi. See also the 2001 table for more recent values.

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
3LiLithium6.941(2) 1, 2, 3, 4
4BeBeryllium 9.012182(3)
5BBoron10.811(7) 1, 2, 3
6CCarbon12.0107(8)1, 2
7NNitrogen 14.00674(7)1, 2
8OOxygen15.9994(3)1, 2
9FFluorine 18.9984032(5)
10NeNeon20.1797(6)1, 3
11NaSodium22.989770(2)
12MgMagnesium 24.3050(6)
13AlAluminium 26.981538(2)
14SiSilicon28.0855(3)2
15PPhosphorus30.973761(2)
16SSulfur32.066(6) 1, 2
17ClChlorine 35.4527(9)3
18ArArgon39.948(1) 1, 2
19KPotassium 39.0983(1)1
20CaCalcium40.078(4) 1
21ScScandium 44.955910(8)
22TiTitanium 47.867(1)
23VVanadium 50.9415(1)
24CrChromium 51.9961(6)
25MnManganese 54.938049(9)
26FeIron55.845(2)
27CoCobalt58.933200(9)
28NiNickel58.6934(2)
29CuCopper63.546(3) 2
30ZnZinc65.39(2)
31GaGallium69.723(1)
32GeGermanium 72.61(2)
33AsArsenic74.92160(2)
34SeSelenium 78.96(3)
35BrBromine79.904(1)
36KrKrypton83.80(1) 1, 3
37RbRubidium 85.4678(3)1
38SrStrontium 87.62(1) 1, 2
39YYttrium88.90585(2)
40ZrZirconium 91.224(2) 1
41NbNiobium92.90638(2)
42MoMolybdenum95.94(1) 1
43TcTechnetium[98] 5
44RuRuthenium101.07(2) 1
45RhRhodium 102.90550(2)
46PdPalladium106.42(1) 1
47AgSilver107.8682(2)1
48CdCadmium 112.411(8) 1
49InIndium114.818(3)
50SnTin118.710(7) 1
51SbAntimony 121.760(1) 1
52TeTellurium127.60(3) 1
53IIodine126.90447(3)
54XeXenon131.29(2) 1, 3
55CsCaesium 132.90545(2)
56BaBarium137.327(7)
57LaLanthanum138.9055(2)1
58CeCerium140.116(1) 1
59PrPraseodymium140.90765(2)
60NdNeodymium144.24(3) 1
61PmPromethium[145] 5
62SmSamarium 150.36(3) 1
63EuEuropium 151.964(1) 1
64GdGadolinium157.25(3) 1
65TbTerbium 158.92534(2)
66DyDysprosium162.50(3) 1
67HoHolmium 164.93032(2)
68ErErbium167.26(3) 1
69TmThulium 168.93421(2)
70YbYtterbium173.04(3) 1
71LuLutetium 174.967(1) 1
72HfHafnium 178.49(2)
73TaTantalum 180.9479(1)
74WTungsten 183.84(1)
75ReRhenium 186.207(1)
76OsOsmium190.23(3) 1
77IrIridium 192.217(3)
78PtPlatinum 195.078(2)
79AuGold196.96655(2)
80HgMercury 200.59(2)
81TlThallium 204.3833(2)
82PbLead207.2(1)1, 2
83BiBismuth 208.98038(2)
84PoPolonium[209] 5
85AtAstatine[210] 5
86RnRadon[222] 5
87FrFrancium[223] 5
88RaRadium [226] 5
89AcActinium[227] 5
90ThThorium 232.0381(1)1, 5
91PaProtactinium231.03588(2)5
92UUranium 238.0289(1)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[263] 5, 6
107BhBohrium [264] 5, 6
108HsHassium [265] 5, 6
109MtMeitnerium[268] 5, 6
110UunUnunnilium[269] 5, 6
111UuuUnununium[272] 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 6.94 and 6.99; if a more accurate value is required, it must be determined for the specific material.
  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 110-111 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).

List of Elements in Name Order.

At NoSymbolNameAtomic
89AcActinium[227] 5
13AlAluminium 26.981538(2)
95AmAmericium[243] 5
51SbAntimony 121.760(1) 1
18ArArgon39.948(1) 1, 2
33AsArsenic74.92160(2)
85AtAstatine[210] 5
56BaBarium137.327(7)
97BkBerkelium[247] 5
4BeBeryllium 9.012182(3)
83BiBismuth 208.98038(2)
107BhBohrium [264] 5, 6
5BBoron10.811(7) 1, 2, 3
35BrBromine79.904(1)
48CdCadmium 112.411(8) 1
55CsCaesium 132.90545(2)
20CaCalcium40.078(4) 1
98CfCalifornium[251] 5
6CCarbon12.0107(8)1, 2
58CeCerium140.116(1) 1
17ClChlorine 35.4527(9)3
24CrChromium 51.9961(6)
27CoCobalt58.933200(9)
29CuCopper63.546(3) 2
96CmCurium [247] 5
105DbDubnium [262] 5, 6
66DyDysprosium162.50(3) 1
99EsEinsteinium[252] 5
68ErErbium167.26(3) 1
63EuEuropium 151.964(1) 1
100FmFermium [257] 5
9FFluorine 18.9984032(5)
87FrFrancium[223] 5
64GdGadolinium157.25(3) 1
31GaGallium69.723(1)
32GeGermanium 72.61(2)
79AuGold196.96655(2)
72HfHafnium 178.49(2)
108HsHassium [265] 5, 6
2HeHelium4.002602(2)1, 2
67HoHolmium 164.93032(2)
1HHydrogen1.00794(7)1, 2, 3
49InIndium114.818(3)
53IIodine126.90447(3)
77IrIridium 192.217(3)
26FeIron55.845(2)
36KrKrypton83.80(1) 1, 3
57LaLanthanum138.9055(2)1
103LrLawrencium[262] 5
82PbLead207.2(1)1, 2
3LiLithium6.941(2) 1, 2, 3, 4
71LuLutetium 174.967(1) 1
12MgMagnesium 24.3050(6)
25MnManganese 54.938049(9)
109MtMeitnerium[268] 5, 6
101MdMendelevium[258] 5
80HgMercury 200.59(2)
42MoMolybdenum95.94(1) 1
60NdNeodymium144.24(3) 1
10NeNeon20.1797(6)1, 3
93NpNeptunium[237] 5
28NiNickel58.6934(2)
41NbNiobium92.90638(2)
7NNitrogen 14.00674(7)1, 2
102NoNobelium[259] 5
76OsOsmium190.23(3) 1
8OOxygen15.9994(3)1, 2
46PdPalladium106.42(1) 1
15PPhosphorus30.973761(2)
78PtPlatinum 195.078(2)
94PuPlutonium[244] 5
84PoPolonium[209] 5
19KPotassium 39.0983(1)1
59PrPraseodymium140.90765(2)
61PmPromethium[145] 5
91PaProtactinium231.03588(2)5
88RaRadium [226] 5
86RnRadon[222] 5
75ReRhenium 186.207(1)
45RhRhodium 102.90550(2)
37RbRubidium 85.4678(3)1
44RuRuthenium101.07(2) 1
104RfRutherfordium[261] 5, 6
62SmSamarium 150.36(3) 1
21ScScandium 44.955910(8)
106SgSeaborgium[263] 5, 6
34SeSelenium 78.96(3)
14SiSilicon28.0855(3)2
47AgSilver107.8682(2)1
11NaSodium22.989770(2)
38SrStrontium 87.62(1) 1, 2
16SSulfur32.066(6) 1, 2
73TaTantalum 180.9479(1)
43TcTechnetium[98] 5
52TeTellurium127.60(3) 1
65TbTerbium 158.92534(2)
81TlThallium 204.3833(2)
90ThThorium 232.0381(1)1, 5
69TmThulium 168.93421(2)
50SnTin118.710(7) 1
22TiTitanium 47.867(1)
74WTungsten 183.84(1)
110UunUnunnilium[269] 5, 6
111UuuUnununium[272] 5, 6
92UUranium 238.0289(1)1, 3, 5
23VVanadium 50.9415(1)
54XeXenon131.29(2) 1, 3
70YbYtterbium173.04(3) 1
39YYttrium88.90585(2)
30ZnZinc65.39(2)
40ZrZirconium 91.224(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 6.94 and 6.99; if a more accurate value is required, it must be determined for the specific material.
  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 110-111 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).

Return to 1997 table

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