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Current Table of Standard Atomic Weights Abridged to Five Significant Digits

Atomic weights of the elements 2013, Meija, J. et al to be published in Pure Appl. Chem. (2014)


Atomic weights listed in the table below are also available in Excel format: "Atomic weights of the elements 2013 (xls)" by Coplen, T. B., Brand, W. A., Meija, J., Gröning, M., Holden, N.E., Berglund, M., De Bièvre, P., Loss, R. D., Prohaska, T., Walczyk, T., published online by CIAAW (2013). [full text - xls 95 KB] {TSAW 2013.xls}


Table of Standard Atomic Weights Abridged to Five Significant Digits
[Using Ar(12C) = 12 as reference, where 12C is an unbound neutral atom in its nuclear and electronic ground state.]

The atomic weights, Ar(E), of many elements vary due to variations in the abundances of their isotopes in natural terrestrial materials. For 12 elements having two or more stable isotopes, an atomic-weight interval is given with the symbol [a, b] to denote the set of atomic-weight values in normal materials; thus, aAr(E) ≤ b for element E. The symbols a and b denote the bounds of the interval [a; b], respectively. Atomic weights are quoted here to five significant figures unless the dependable accuracy is further 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 the elements annotated r). Excluding values given as atomic-weight intervals, 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 values by more than one 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 with no stable isotope do not have an atomic weight and such entries have a blank 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 value is tabulated. For more detailed information, users should refer to the full IUPAC Table of Standard Atomic Weights.

Order of Atomic Number

Atomic Number

Element Name

Symbol

Atomic Weight

Footnotes

1

hydrogen

H

[1.0078, 1.0082]

m

2

helium

He

4.0026

 

3

lithium

Li

[6.938, 6.997]

m

4

beryllium

Be

9.0122

 

5

boron

B

[10.806, 10.821]

m

6

carbon

C

[12.009, 12.012]

 

7

nitrogen

N

[14.006, 14.008]

 

8

oxygen

O

[15.999, 16.000]

 

9

fluorine

F

18.998

 

10

neon

Ne

20.180

m

11

sodium

Na

22.990

 

12

magnesium

Mg

[24.304, 24.307]

 

13

aluminium (aluminum)

Al

26.982

 

14

silicon

Si

[28.084, 28.086]

 

15

phosphorus

P

30.974

 

16

sulfur

S

[32.059, 32.076]

 

17

chlorine

Cl

[35.446, 35.457]

m

18

argon

Ar

39.948

g r

19

potassium

K

39.098

g

20

calcium

Ca

40.078(4)

g

21

scandium

Sc

44.956

 

22

titanium

Ti

47.867

 

23

vanadium

V

50.942

 

24

chromium

Cr

51.996

 

25

manganese

Mn

54.938

 

26

iron

Fe

55.845(2)

 

27

cobalt

Co

58.933

 

28

nickel

Ni

58.693

r

29

copper

Cu

63.546(3)

r

30

zinc

Zn

65.38(2)

r

31

gallium

Ga

69.723

 

32

germanium

Ge

72.630(8)

 

33

arsenic

As

74.922

 

34

selenium

Se

78.971(8)

r

35

bromine

Br

[79.901, 79.907]

 

36

krypton

Kr

83.798(2)

g m

37

rubidium

Rb

85.468

 

38

strontium

Sr

87.62

g r

39

yttrium

Y

88.906

 

40

zirconium

Zr

91.224(2)

g

41

niobium

Nb

92.906

 

42

molybdenum

Mo

95.95

g

43

technetium*

Tc

 

 

44

ruthenium

Ru

101.07(2)

g

45

rhodium

Rh

102.91

 

46

palladium

Pd

106.42

g

47

silver

Ag

107.87

g

48

cadmium

Cd

112.41

 

49

indium

In

114.82

 

50

tin

Sn

118.71

 

51

antimony

Sb

121.76

g

52

tellurium

Te

127.60(3)

g

53

iodine

I

126.90

 

54

xenon

Xe

131.29

g m

55

caesium (cesium)

Cs

132.91

 

56

barium

Ba

137.33

 

57

lanthanum

La

138.91

 

58

cerium

Ce

140.12

g

59

praseodymium

Pr

140.91

 

60

neodymium

Nd

144.24

g

61

promethium*

Pm

 

 

62

samarium

Sm

150.36(2)

g

63

europium

Eu

151.96

g

64

gadolinium

Gd

157.25(3)

g

65

terbium

Tb

158.93

 

66

dysprosium

Dy

162.50

g

67

holmium

Ho

164.93

 

68

erbium

Er

167.26

g

69

thulium

Tm

168.93

 

70

ytterbium

Yb

173.05

g

71

lutetium

Lu

174.97

g

72

hafnium

Hf

178.49(2)

 

73

tantalum

Ta

180.95

 

74

tungsten

W

183.84

 

75

rhenium

Re

186.21

 

76

osmium

Os

190.23(3)

g

77

iridium

Ir

192.22

 

78

platinum

Pt

195.08

 

79

gold

Au

196.97

 

80

mercury

Hg

200.59

 

81

thallium

Tl

[204.38, 204.39]

 

82

lead

Pb

207.2

g r

83

bismuth

Bi

208.98

 

84

polonium*

Po

 

 

85

astatine*

At

 

 

86

radon*

Rn

 

 

87

francium*

Fr

 

 

88

radium*

Ra

 

 

89

actinium*

Ac

 

 

90

thorium*

Th

232.04

g

91

protactinium*

Pa

231.04

 

92

uranium*

U

238.03

g m

93

neptunium*

Np

 

 

94

plutonium*

Pu

 

 

95

americium*

Am

 

 

96

curium*

Cm

 

 

97

berkelium*

Bk

 

 

98

californium*

Cf

 

 

99

einsteinium*

Es

 

 

100

fermium*

Fm

 

 

101

mendelevium*

Md

 

 

102

nobelium*

No

 

 

103

lawrencium*

Lr

 

 

104

rutherfordium*

Rf

 

 

105

dubnium*

Db

 

 

106

seaborgium*

Sg

 

 

107

bohrium*

Bh

 

 

108

hassium*

Hs

 

 

109

meitnerium*

Mt

 

 

110

darmstadtium*

Ds

 

 

111

roentgenium*

Rg

 

 

112

copernicium*

Cn

 

 

113

ununtrium*

Uut

 

 

114

flerovium*

Fl

 

 

115

ununpentium*

Uup

 

 

116

livermorium*

Lv

 

 

118

ununoctium*

Uuo

 

 

*Element has no stable isotopes. One or more well-known isotopes are given in Table 3 with the appropriate relative atomic mass and half-life. However, three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.

g 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.

m Modified isotopic compositions may be found in commercially available material because it has been subjected to an undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.

r Range in isotopic composition of normal terrestrial material prevents a more precise Ar(E) being given; the tabulated Ar(E) value and uncertainty should be applicable to normal material.

 

 
2010 Commission on Isotopic Abundances and Atomic Weights | a commission of the International Union of Pure and Applied Chemistry