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Current Table of Standard Atomic Weights Abridged to Five Significant Figures

Atomic Weights of the Elements 1993, Pure Appl. Chem. 66, 2423-2444 (1994). [full text - pdf 1200 KB] {TSAW 1993.pdf}

Table of Standard Atomic Weights Abridged to Five Significant Figures
Atomic weights, scaled to the relative atomic mass, Ar(12C) = 12, are here quoted to five significant figures unless the dependable accuracy is more limited by either the combined uncertainties of the best published atomic weight determinations, or by the variability of isotopic composition in normal terrestrial occurrences (the latter applies to elements annotated r).  The last significant figure of each tabulated value is considered reliable to ±1 except when a larger single digit uncertainty is inserted in parentheses following the atomic weight.  Neither the highest nor the lowest actual atomic weight of any normal sample is thought likely to differ from the tabulated value by more than the assigned uncertainty.  However, the tabulated values do not apply either to samples of highly exceptional isotopic composition arising from most unusual geological occurrences (for elements annotated g) or to those whose isotopic composition has been artificially altered.  Such might even be found in commerce without disclosure of that modification (for elements annotated m).  Elements annotated by an asterisk (*) have no stable isotope and are generally represented in this Table by just one of the element's commonly known radioisotopes, with a corresponding relative atomic mass in the atomic weight column.  However, three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.  For more detailed information users should refer to the full IUPAC Table of Standard Atomic Weights.

Alphabetical Order in English

Name

Symbol

Number

Atomic Weight

Footnotes

Actinium*

227Ac

89

227.03

 

Aluminium (Aluminum)

Al

13

26.982

 

Americium*

241Am

95

241.06

 

Antimony (Stibium)

Sb

51

121.76

g

Argon

Ar

18

39.948

g r

Arsenic

As

33

74.922

 

Astatine*

210At

85

209.99

 

Barium

Ba

56

137.33

 

Berkelium*

249Bk

97

249.08

 

Beryllium

Be

4

9.0122

 

Bismuth

Bi

83

208.98

 

Boron

B

5

10.811(5)

g m r

Bromine

Br

35

79.904

 

Cadmium

Cd

48

112.41

 

Caesium (Cesium)

Cs

55

132.91

 

Calcium

Ca

20

40.078(4)

g

Californium*

252Cf

98

252.08

 

Carbon

C

6

12.011

g r

Cerium

Ce

58

140.12

g

Chlorine

Cl

17

35.453

m

Chromium

Cr

24

51.996

 

Cobalt

Co

27

58.933

 

Copper (Cuprum)

Cu

29

63.546(3)

r

Curium*

244Cm

96

244.06

 

Dysprosium

Dy

66

162.50(3)

g

Einsteinium*

252Es

99

252.08

 

Erbium

Er

68

167.26(3)

g

Europium

Eu

63

151.96

g

Fermium*

257Fm

100

257.10

 

Fluorine

F

9

18.998

 

Francium*

223Fr

87

223.02

 

Gadolinium

Gd

64

157.25(3)

g

Gallium

Ga

31

69.723

 

Germanium

Ge

32

72.61(2)

 

Gold (Aurum)

Au

79

196.97

 

Hafnium

Hf

72

178.49(2)

 

Helium

He

2

4.0026

 

Holmium

Ho

67

164.93

 

Hydrogen

H

1

1.007 9

g m

Indium

In

49

114.82

 

Iodine

I

53

126.90

 

Iridium

Ir

77

192.22

 

Iron (Ferrum)

Fe

26

55.845(2)

 

Krypton

Kr

36

83.80

g m

Lanthanum

La

57

138.91

 

Lawrencium*

262Lr

103

262.11

 

Lead (Plumbum)

Pb

82

207.2

g r

Lithium

Li

3

[6.941(2)]†

g m r

Lutetium

Lu

71

174.97

g

Magnesium

Mg

12

24.305

 

Manganese

Mn

25

54.938

 

Mendelevium*

258Md

101

258.10

 

Mercury (Hydrargyrum)

Hg

80

200.59(2)

 

Molybdenum

Mo

42

95.94

g

Neodymium

Nd

60

144.24(3)

g

Neon

Ne

10

20.180

m

Neptunium*

237Np

93

237.05

 

Nickel

Ni

28

58.693

 

Niobium

Nb

41

92.906

 

Nitrogen

N

7

14.007

 

Nobelium*

259No

102

259.10

 

Osmium

Os

76

190.23(3)

g

Oxygen

O

8

15.999

 

Palladium

Pd

46

106.42

g

Phosphorus

P

15

30.974

 

Platinum

Pt

78

195.08(3)

 

Plutonium*

239Pu

94

239.05

 

Polonium*

210Po

84

209.98

 

Potassium (Kalium)

K

19

39.098

g

Praseodymium

Pr

59

140.91

 

Promethium*

147Pm

61

146.92

 

Protactinium*

Pa

91

231.04

 

Radium*

226Ra

88

226.03

 

Radon*

222Rn

86

222.02

 

Rhenium

Re

75

186.21

 

Rhodium

Rh

45

102.91

 

Rubidium

Rb

37

85.468

 

Ruthenium

Ru

44

101.07(2)

g

Samarium

Sm

62

150.36(3)

g

Scandium

Sc

21

44.956

 

Selenium

Se

34

78.96(3)

 

Silicon

Si

14

28.086

 

Silver (Argentum)

Ag

47

107.87

 

Sodium (Natrium)

Na

11

22.990

 

Strontium

Sr

38

87.62

g r

Sulfur

S

16

32.066(6)

g r

Tantalum

Ta

73

180.95

 

Technetium*

99Tc

43

98.906

 

Tellurium

Te

52

127.60(3)

g

Terbium

Tb

65

158.93

 

Thallium

Tl

81

204.38

 

Thorium*

Th

90

232.04

g

Thulium

Tm

69

168.93

 

Tin (Stannum)

Sn

50

118.71

 

Titanium

Ti

22

47.867

 

Tungsten (Wolfram)

W

74

183.84

 

Ununbium*

Uub

112

 

 

Ununhexium*

Uuh

116

 

 

Ununoctium*

Uuo

118

 

 

Ununpentium*

Uup

115

 

 

Ununquadium*

Uuq

114

 

 

Ununtrium*

Uut

113

 

 

Uranium*

U

92

238.03

g m

Vanadium

V

23

50.942

 

Xenon

Xe

54

131.29(2)

g m

Ytterbium

Yb

70

173.04(3)

g

Yttrium

Y

39

88.906

 

Zinc

Zn

30

65.39(2)

 

Zirconium

Zr

40

91.224(2)

g

†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.

 

 

 
2008 Commission on Isotopic Abundances and Atomic Weights | a commission of the International Union of Pure and Applied Chemistry