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

https://www.qmul.ac.uk/sbcs/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.

List of Elements in Atomic Number Order.

At No Symbol Name Atomic Wt Notes

1 H Hydrogen 1.00794(7) 1, 2, 3

2 He Helium 4.002602(2) 1, 2

3 Li Lithium [6.941(2)] 1, 2, 3, 4

4 Be Beryllium 9.012182(3)

5 B Boron 10.811(7) 1, 2, 3

6 C Carbon 12.0107(8) 1, 2

7 N Nitrogen 14.0067(2) 1, 2

8 O Oxygen 15.9994(3) 1, 2

9 F Fluorine 18.9984032(5)

10 Ne Neon 20.1797(6) 1, 3

11 Na Sodium 22.98976928(2)

12 Mg Magnesium 24.3050(6)

13 Al Aluminium 26.9815386(8)

14 Si Silicon 28.0855(3) 2

15 P Phosphorus 30.973762(2)

16 S Sulfur 32.065(5) 1, 2

17 Cl Chlorine 35.453(2) 3

18 Ar Argon 39.948(1) 1, 2

19 K Potassium 39.0983(1) 1

20 Ca Calcium 40.078(4) 1

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)

29 Cu Copper 63.546(3) 2

30 Zn Zinc 65.38(2)

31 Ga Gallium 69.723(1)

32 Ge Germanium 72.64(1)

33 As Arsenic 74.92160(2)

34 Se Selenium 78.96(3)

35 Br Bromine 79.904(1)

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 [98] 5

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(3)

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 200.59(2)

81 Tl Thallium 204.3833(2)

82 Pb Lead 207.2(1) 1, 2

83 Bi Bismuth 208.98040(1)

84 Po Polonium [209] 5

85 At Astatine [210] 5

86 Rn Radon [222] 5

87 Fr Francium [223] 5

88 Ra Radium [226] 5

89 Ac Actinium [227] 5

90 Th Thorium 232.03806(2) 1, 5

91 Pa Protactinium 231.03588(2) 5

92 U Uranium 238.02891(3) 1, 3, 5

93 Np Neptunium [237] 5

94 Pu Plutonium [244] 5

95 Am Americium [243] 5

96 Cm Curium [247] 5

97 Bk Berkelium [247] 5

98 Cf Californium [251] 5

99 Es Einsteinium [252] 5

100 Fm Fermium [257] 5

101 Md Mendelevium [258] 5

102 No Nobelium [259] 5

103 Lr Lawrencium [262] 5

104 Rf Rutherfordium [265] 5

105 Db Dubnium [268] 5

106 Sg Seaborgium [271] 5

107 Bh Bohrium [272] 5

108 Hs Hassium [270] 5

109 Mt Meitnerium [276] 5

110 Ds Darmstadtium [281] 5

111 Rg Roentgenium [280] 5

112 Cn Copernicium [285] 5, 6

113 Uut Ununtrium [284] 5, 6

114 Uuq Ununquadium [289] 5, 6

115 Uup Ununpentium [288] 5, 6

116 Uuh Ununhexium [293] 5, 6

117 Uus Ununseptium 5, 6

118 Uuo Ununoctium [294] 5, 6

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.
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].
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 113-118 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 No Symbol Name Atomic Wt Notes

89 Ac Actinium [227] 5

13 Al Aluminium 26.9815386(8)

95 Am Americium [243] 5

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] 5

56 Ba Barium 137.327(7)

97 Bk Berkelium [247] 5

4 Be Beryllium 9.012182(3)

83 Bi Bismuth 208.98040(1)

107 Bh Bohrium [272] 5

5 B Boron 10.811(7) 1, 2, 3

35 Br Bromine 79.904(1)

48 Cd Cadmium 112.411(8) 1

55 Cs Caesium 132.9054519(2)

20 Ca Calcium 40.078(4) 1

98 Cf Californium [251] 5

6 C Carbon 12.0107(8) 1, 2

58 Ce Cerium 140.116(1) 1

17 Cl Chlorine 35.453(2) 3

24 Cr Chromium 51.9961(6)

27 Co Cobalt 58.933195(5)

112 Cn Copernicium [285] 5, 6

29 Cu Copper 63.546(3) 2

96 Cm Curium [247] 5

110 Ds Darmstadtium [281] 5

105 Db Dubnium [268] 5

66 Dy Dysprosium 162.500(1) 1

99 Es Einsteinium [252] 5

68 Er Erbium 167.259(3) 1

63 Eu Europium 151.964(1) 1

100 Fm Fermium [257] 5

9 F Fluorine 18.9984032(5)

87 Fr Francium [223] 5

64 Gd Gadolinium 157.25(3) 1

31 Ga Gallium 69.723(1)

32 Ge Germanium 72.64(1)

79 Au Gold 196.966569(4)

72 Hf Hafnium 178.49(2)

108 Hs Hassium [270] 5

2 He Helium 4.002602(2) 1, 2

67 Ho Holmium 164.93032(2)

1 H Hydrogen 1.00794(7) 1, 2, 3

49 In Indium 114.818(3)

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] 5

82 Pb Lead 207.2(1) 1, 2

3 Li Lithium [6.941(2)] 1, 2, 3, 4

71 Lu Lutetium 174.9668(1) 1

12 Mg Magnesium 24.3050(6)

25 Mn Manganese 54.938045(5)

109 Mt Meitnerium [276] 5

101 Md Mendelevium [258] 5

80 Hg Mercury 200.59(2)

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] 5

28 Ni Nickel 58.6934(4)

41 Nb Niobium 92.90638(2)

7 N Nitrogen 14.0067(2) 1, 2

102 No Nobelium [259] 5

76 Os Osmium 190.23(3) 1

8 O Oxygen 15.9994(3) 1, 2

46 Pd Palladium 106.42(1) 1

15 P Phosphorus 30.973762(2)

78 Pt Platinum 195.084(9)

94 Pu Plutonium [244] 5

84 Po Polonium [209] 5

19 K Potassium 39.0983(1) 1

59 Pr Praseodymium 140.90765(2)

61 Pm Promethium [145] 5

91 Pa Protactinium 231.03588(2) 5

88 Ra Radium [226] 5

86 Rn Radon [222] 5

75 Re Rhenium 186.207(1)

45 Rh Rhodium 102.90550(2)

111 Rg Roentgenium [280] 5

37 Rb Rubidium 85.4678(3) 1

44 Ru Ruthenium 101.07(2) 1

104 Rf Rutherfordium [265] 5

62 Sm Samarium 150.36(2) 1

21 Sc Scandium 44.955912(6)

106 Sg Seaborgium [271] 5

34 Se Selenium 78.96(3)

14 Si Silicon 28.0855(3) 2

47 Ag Silver 107.8682(2) 1

11 Na Sodium 22.98976928(2)

38 Sr Strontium 87.62(1) 1, 2

16 S Sulfur 32.065(5) 1, 2

73 Ta Tantalum 180.94788(2)

43 Tc Technetium [98] 5

52 Te Tellurium 127.60(3) 1

65 Tb Terbium 158.92535(2)

81 Tl Thallium 204.3833(2)

90 Th Thorium 232.03806(2) 1, 5

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)

116 Uuh Ununhexium [293] 5, 6

118 Uuo Ununoctium [294] 5, 6

115 Uup Ununpentium [288] 5, 6

114 Uuq Ununquadium [289] 5, 6

117 Uus Ununseptium 5, 6

113 Uut Ununtrium [284] 5, 6

92 U Uranium 238.02891(3) 1, 3, 5

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)

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.
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].
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 113-118 are under review. The temporary system recommended by J Chatt, Pure Appl. Chem., 51, 381-384 (1979) is used above.

Return to IUPAC Chemical Nomenclature home page

At No	Symbol	Name	Atomic Wt	Notes
1	H	Hydrogen	1.00794(7)	1, 2, 3
2	He	Helium	4.002602(2)	1, 2
3	Li	Lithium	[6.941(2)]	1, 2, 3, 4
4	Be	Beryllium	9.012182(3)
5	B	Boron	10.811(7)	1, 2, 3
6	C	Carbon	12.0107(8)	1, 2
7	N	Nitrogen	14.0067(2)	1, 2
8	O	Oxygen	15.9994(3)	1, 2
9	F	Fluorine	18.9984032(5)
10	Ne	Neon	20.1797(6)	1, 3
11	Na	Sodium	22.98976928(2)
12	Mg	Magnesium	24.3050(6)
13	Al	Aluminium	26.9815386(8)
14	Si	Silicon	28.0855(3)	2
15	P	Phosphorus	30.973762(2)
16	S	Sulfur	32.065(5)	1, 2
17	Cl	Chlorine	35.453(2)	3
18	Ar	Argon	39.948(1)	1, 2
19	K	Potassium	39.0983(1)	1
20	Ca	Calcium	40.078(4)	1
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)
29	Cu	Copper	63.546(3)	2
30	Zn	Zinc	65.38(2)
31	Ga	Gallium	69.723(1)
32	Ge	Germanium	72.64(1)
33	As	Arsenic	74.92160(2)
34	Se	Selenium	78.96(3)
35	Br	Bromine	79.904(1)
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	[98]	5
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(3)
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	200.59(2)
81	Tl	Thallium	204.3833(2)
82	Pb	Lead	207.2(1)	1, 2
83	Bi	Bismuth	208.98040(1)
84	Po	Polonium	[209]	5
85	At	Astatine	[210]	5
86	Rn	Radon	[222]	5
87	Fr	Francium	[223]	5
88	Ra	Radium	[226]	5
89	Ac	Actinium	[227]	5
90	Th	Thorium	232.03806(2)	1, 5
91	Pa	Protactinium	231.03588(2)	5
92	U	Uranium	238.02891(3)	1, 3, 5
93	Np	Neptunium	[237]	5
94	Pu	Plutonium	[244]	5
95	Am	Americium	[243]	5
96	Cm	Curium	[247]	5
97	Bk	Berkelium	[247]	5
98	Cf	Californium	[251]	5
99	Es	Einsteinium	[252]	5
100	Fm	Fermium	[257]	5
101	Md	Mendelevium	[258]	5
102	No	Nobelium	[259]	5
103	Lr	Lawrencium	[262]	5
104	Rf	Rutherfordium	[265]	5
105	Db	Dubnium	[268]	5
106	Sg	Seaborgium	[271]	5
107	Bh	Bohrium	[272]	5
108	Hs	Hassium	[270]	5
109	Mt	Meitnerium	[276]	5
110	Ds	Darmstadtium	[281]	5
111	Rg	Roentgenium	[280]	5
112	Cn	Copernicium	[285]	5, 6
113	Uut	Ununtrium	[284]	5, 6
114	Uuq	Ununquadium	[289]	5, 6
115	Uup	Ununpentium	[288]	5, 6
116	Uuh	Ununhexium	[293]	5, 6
117	Uus	Ununseptium		5, 6
118	Uuo	Ununoctium	[294]	5, 6