IUPAC Commission on Isotopic Abundances and Atomic Weights.

ATOMIC WEIGHTS OF THE ELEMENTS 2011

These tables are based on the 2011 table at Pure Appl. Chem., 2013, 85, 1047-1078 with changes from the 2009 table for the values of bromine, germanium, indium, magnesium, and mercury.

https://iupac.qmul.ac.uk/AtWt/

A PDF of the 2011 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, the 2005 table, the 2007 table or the 2009 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

1 H hydrogen 1.007 84 1.008 11

3 Li lithium 6.938 6.997

5 B boron 10.806 10.821

6 C carbon 12.0096 12.0116

7 N nitrogen 14.006 43 14.007 28

8 O oxygen 15.999 03 15.999 77

12 Mg magnesium 24.30 24.31

14 Si silicon 28.084 28.086

16 S sulfur 32.059 32.076

17 Cl chlorine 35.446 35.457

35 Br bromine 79.90 79.91

81 Tl thallium 204.382 204.385

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

Table 2. List of Elements in Atomic Number Order.

At No Symbol Name Atomic Wt Notes

1 H Hydrogen 1.008 3, 6

2 He Helium 4.002602(2) 1, 2

3 Li Lithium 6.94 3, 6

4 Be Beryllium 9.012182(3)

5 B Boron 10.81 3, 6

6 C Carbon 12.011 6

7 N Nitrogen 14.007 6

8 O Oxygen 15.999 6

9 F Fluorine 18.9984032(5)

10 Ne Neon 20.1797(6) 1, 3

11 Na Sodium 22.98976928(2)

12 Mg Magnesium 24.305 6

13 Al Aluminium 26.9815386(8)

14 Si Silicon 28.085 6

15 P Phosphorus 30.973762(2)

16 S Sulfur 32.06 6

17 Cl Chlorine 35.45 3, 6

18 Ar Argon 39.948(1) 1, 2

19 K Potassium 39.0983(1)

20 Ca Calcium 40.078(4)

21 Sc Scandium 44.955912(6)

22 Ti Titanium 47.867(1)

23 V Vanadium 50.9415(1)

24 Cr Chromium 51.9961(6)

25 Mn Manganese 54.938045(5)

26 Fe Iron 55.845(2)

27 Co Cobalt 58.933195(5)

28 Ni Nickel 58.6934(4) 2

29 Cu Copper 63.546(3) 2

30 Zn Zinc 65.38(2) 2

31 Ga Gallium 69.723(1)

32 Ge Germanium 72.630(8)

33 As Arsenic 74.92160(2)

34 Se Selenium 78.96(3)

35 Br Bromine 79.904 6

36 Kr Krypton 83.798(2) 1, 3

37 Rb Rubidium 85.4678(3) 1

38 Sr Strontium 87.62(1) 1, 2

39 Y Yttrium 88.90585(2)

40 Zr Zirconium 91.224(2) 1

41 Nb Niobium 92.90638(2)

42 Mo Molybdenum 95.96(2) 1

43 Tc Technetium [97] 4

44 Ru Ruthenium 101.07(2) 1

45 Rh Rhodium 102.90550(2)

46 Pd Palladium 106.42(1) 1

47 Ag Silver 107.8682(2) 1

48 Cd Cadmium 112.411(8) 1

49 In Indium 114.818(1)

50 Sn Tin 118.710(7) 1

51 Sb Antimony 121.760(1) 1

52 Te Tellurium 127.60(3) 1

53 I Iodine 126.90447(3)

54 Xe Xenon 131.293(6) 1, 3

55 Cs Caesium 132.9054519(2)

56 Ba Barium 137.327(7)

57 La Lanthanum 138.90547(7) 1

58 Ce Cerium 140.116(1) 1

59 Pr Praseodymium 140.90765(2)

60 Nd Neodymium 144.242(3) 1

61 Pm Promethium [145] 5

62 Sm Samarium 150.36(2) 1

63 Eu Europium 151.964(1) 1

64 Gd Gadolinium 157.25(3) 1

65 Tb Terbium 158.92535(2)

66 Dy Dysprosium 162.500(1) 1

67 Ho Holmium 164.93032(2)

68 Er Erbium 167.259(3) 1

69 Tm Thulium 168.93421(2)

70 Yb Ytterbium 173.054(5) 1

71 Lu Lutetium 174.9668(1) 1

72 Hf Hafnium 178.49(2)

73 Ta Tantalum 180.94788(2)

74 W Tungsten 183.84(1)

75 Re Rhenium 186.207(1)

76 Os Osmium 190.23(3) 1

77 Ir Iridium 192.217(3)

78 Pt Platinum 195.084(9)

79 Au Gold 196.966569(4)

80 Hg Mercury 200.592(3)

81 Tl Thallium 204.38 6

82 Pb Lead 207.2(1) 1, 2

83 Bi Bismuth 208.98040(1)

84 Po Polonium [209] 4

85 At Astatine [210] 4

86 Rn Radon [222] 4

87 Fr Francium [223] 4

88 Ra Radium [226] 4

89 Ac Actinium [227] 4

90 Th Thorium 232.03806(2) 1, 4

91 Pa Protactinium 231.03588(2) 4

92 U Uranium 238.02891(3) 1, 3, 4

93 Np Neptunium [237] 4

94 Pu Plutonium [244] 4

95 Am Americium [243] 4

96 Cm Curium [247] 4

97 Bk Berkelium [247] 4

98 Cf Californium [251] 4

99 Es Einsteinium [252] 4

100 Fm Fermium [257] 4

101 Md Mendelevium [258] 4

102 No Nobelium [259] 4

103 Lr Lawrencium [262] 4

104 Rf Rutherfordium [267] 4

105 Db Dubnium [270] 4

106 Sg Seaborgium [271] 4

107 Bh Bohrium [270] 4

108 Hs Hassium [277] 4

109 Mt Meitnerium [276] 4

110 Ds Darmstadtium [281] 4

111 Rg Roentgenium [282] 4

112 Cn Copernicium [285] 4

113 Uut Ununtrium [285] 4, 5

114 Fl Flerovium [289] 4, 5

115 Uup Ununpentium [2889] 4, 5

116 Lv Livermorium [293] 4, 5

117 Uus Ununseptium [294] 4, 5

118 Uuo Ununoctium [294] 4, 5

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.
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.
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.
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.
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.
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 Name Atomic Wt Notes

89 Ac Actinium [227] 4

13 Al Aluminium 26.9815386(8)

95 Am Americium [243] 4

51 Sb Antimony 121.760(1) 1

18 Ar Argon 39.948(1) 1, 2

33 As Arsenic 74.92160(2)

85 At Astatine [210] 4

56 Ba Barium 137.327(7)

97 Bk Berkelium [247] 4

4 Be Beryllium 9.012182(3)

83 Bi Bismuth 208.98040(1)

107 Bh Bohrium [270] 4

5 B Boron 10.81 3, 6

35 Br Bromine 79.904 6

48 Cd Cadmium 112.411(8) 1

55 Cs Caesium 132.9054519(2)

20 Ca Calcium 40.078(4) 1

98 Cf Californium [251] 4

6 C Carbon 12.011 6

58 Ce Cerium 140.116(1) 1

17 Cl Chlorine 35.45 3, 6

24 Cr Chromium 51.9961(6)

27 Co Cobalt 58.933195(5)

112 Cn Copernicium [285] 4

29 Cu Copper 63.546(3) 2

96 Cm Curium [247] 4

110 Ds Darmstadtium [281] 4

105 Db Dubnium [270] 4

66 Dy Dysprosium 162.500(1) 1

99 Es Einsteinium [252] 4

68 Er Erbium 167.259(3) 1

63 Eu Europium 151.964(1) 1

100 Fm Fermium [257] 4

114 Fl Flerovium [289] 4, 5

9 F Fluorine 18.9984032(5)

87 Fr Francium [223] 4

64 Gd Gadolinium 157.25(3) 1

31 Ga Gallium 69.723(1)

32 Ge Germanium 72.630(8)

79 Au Gold 196.966569(4)

72 Hf Hafnium 178.49(2)

108 Hs Hassium [277] 4

2 He Helium 4.002602(2) 1, 2

67 Ho Holmium 164.93032(2)

1 H Hydrogen 1.008 3, 6

49 In Indium 114.818(1)

53 I Iodine 126.90447(3)

77 Ir Iridium 192.217(3)

26 Fe Iron 55.845(2)

36 Kr Krypton 83.798(2) 1, 3

57 La Lanthanum 138.90547(7) 1

103 Lr Lawrencium [262] 4

82 Pb Lead 207.2(1) 1, 2

3 Li Lithium 6.94 3, 6

116 Lv Livermorium [293] 4, 5

71 Lu Lutetium 174.9668(1) 1

12 Mg Magnesium 24.305 6

25 Mn Manganese 54.938045(5)

109 Mt Meitnerium [276] 4

101 Md Mendelevium [258] 4

80 Hg Mercury 200.592(3)

42 Mo Molybdenum 95.96(2) 1

60 Nd Neodymium 144.242(3) 1

10 Ne Neon 20.1797(6) 1, 3

93 Np Neptunium [237] 4

28 Ni Nickel 58.6934(4)

41 Nb Niobium 92.90638(2)

7 N Nitrogen 14.007 6

102 No Nobelium [259] 4

76 Os Osmium 190.23(3) 1

8 O Oxygen 15.999 6

46 Pd Palladium 106.42(1) 1

15 P Phosphorus 30.973762(2)

78 Pt Platinum 195.084(9)

94 Pu Plutonium [244] 4

84 Po Polonium [209] 4

19 K Potassium 39.0983(1)

59 Pr Praseodymium 140.90765(2)

61 Pm Promethium [145] 4

91 Pa Protactinium 231.03588(2) 4

88 Ra Radium [226] 4

86 Rn Radon [222] 4

75 Re Rhenium 186.207(1)

45 Rh Rhodium 102.90550(2)

111 Rg Roentgenium [282] 4

37 Rb Rubidium 85.4678(3) 1

44 Ru Ruthenium 101.07(2) 1

104 Rf Rutherfordium [267] 4

62 Sm Samarium 150.36(2) 1

21 Sc Scandium 44.955912(6)

106 Sg Seaborgium [271] 4

34 Se Selenium 78.96(3)

14 Si Silicon 28.085 6

47 Ag Silver 107.8682(2) 1

11 Na Sodium 22.98976928(2)

38 Sr Strontium 87.62(1) 1, 2

16 S Sulfur 32.06 6

73 Ta Tantalum 180.94788(2)

43 Tc Technetium [97] 4

52 Te Tellurium 127.60(3) 1

65 Tb Terbium 158.92535(2)

81 Tl Thallium 204.38 6

90 Th Thorium 232.03806(2) 1, 4

69 Tm Thulium 168.93421(2)

50 Sn Tin 118.710(7) 1

22 Ti Titanium 47.867(1)

74 W Tungsten 183.84(1)

118 Uuo Ununoctium [294] 4, 5

115 Uup Ununpentium [289] 4, 5

117 Uus Ununseptium [294] 4, 5

113 Uut Ununtrium [285] 4, 5

92 U Uranium 238.02891(3) 1, 3, 4

23 V Vanadium 50.9415(1)

54 Xe Xenon 131.293(6) 1, 3

70 Yb Ytterbium 173.054(5) 1

39 Y Yttrium 88.90585(2)

30 Zn Zinc 65.38(2) 2

40 Zr Zirconium 91.224(2) 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.
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.
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.
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.
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.
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

At No	Symbol	Name	Minimum Atomic Wt	Maximum Atomic Wt
1	H	hydrogen	1.007 84	1.008 11
3	Li	lithium	6.938	6.997
5	B	boron	10.806	10.821
6	C	carbon	12.0096	12.0116
7	N	nitrogen	14.006 43	14.007 28
8	O	oxygen	15.999 03	15.999 77
12	Mg	magnesium	24.30	24.31
14	Si	silicon	28.084	28.086
16	S	sulfur	32.059	32.076
17	Cl	chlorine	35.446	35.457
35	Br	bromine	79.90	79.91
81	Tl	thallium	204.382	204.385