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Current Table of Standard Atomic Weights in Alphabetical Order

Standard 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 2013
[Using Ar(12C) = 12 as reference, where 12C is an unbound neutral atom in its nuclear and electronic ground state.]

The atomic weights of many elements are not invariant, but depend on the origin and treatment of the material. The standard values of Ar(E) and the uncertainties (in parentheses, following the last significant figure to which they are attributed) apply to elements of natural terrestrial origin. The footnotes to this table elaborate the types of variation that may occur for individual elements and that may be larger than the listed uncertainties of values ofAr(E). Names of elements with atomic numbers 112 to 118 are provisional.

The atomic weights, Ar(E), of many elements vary due to variations in the abundances of their isotopes in natural terrestrial materials. For 10 of these elements, 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]. If a more accurate Ar(E) value is required, it must be determined for the specific material. For 74 elements, Ar(E) values and their decisional uncertainties (in parentheses, following the last significant figure to which they are attributed) are given. The footnotes to this table elaborate the types of variation that may occur for individual elements and that may be larger than the listed uncertainties of values of Ar(E) or may lie outside the values listed.

Alphabetical Order in English

Name

Symbol

Atomic Number

Standard Atomic Weight

Footnotes

actinium*

Ac

89

 

 

aluminium (aluminum)

Al

13

26.981 5385(7)

 

americium*

Am

95

 

 

antimony

Sb

51

121.760(1)

g

argon

Ar

18

39.948(1)

g r

arsenic

As

33

74.921 595(6)

 

astatine*

At

85

 

 

barium

Ba

56

137.327(7)

 

berkelium*

Bk

97

 

 

beryllium

Be

4

9.012 1831(5)

 

bismuth

Bi

83

208.980 40(1)

 

bohrium*

Bh

107

 

 

boron

B

5

[10.806, 10.821]

m

bromine

Br

35

[79.901, 79.907]

 

cadmium

Cd

48

112.414(4)

g

caesium (cesium)

Cs

55

132.905 451 96(6)

 

calcium

Ca

20

40.078(4)

g

californium*

Cf

98

 

 

carbon

C

6

[12.0096, 12.0116]

 

cerium

Ce

58

140.116(1)

g

chlorine

Cl

17

[35.446, 35.457]

m

chromium

Cr

24

51.9961(6)

 

cobalt

Co

27

58.933 194(4)

 

copernicium*

Cn

112

 

 

copper

Cu

29

63.546(3)

r

curium*

Cm

96

 

 

darmstadtium*

Ds

110

 

 

dubnium*

Db

105

 

 

dysprosium

Dy

66

162.500(1)

g

einsteinium*

Es

99

 

 

erbium

Er

68

167.259(3)

g

europium

Eu

63

151.964(1)

g

fermium*

Fm

100

 

 

flerovium*

Fl

114

 

 

fluorine

F

9

18.998 403 163(6)

 

francium*

Fr

87

 

 

gadolinium

Gd

64

157.25(3)

g

gallium

Ga

31

69.723(1)

 

germanium

Ge

32

72.630(8)

 

gold

Au

79

196.966 569(5)

 

hafnium

Hf

72

178.49(2)

 

hassium*

Hs

108

 

 

helium

He

2

4.002 602(2)

 g r

holmium

Ho

67

164.930 33(2)

 

hydrogen

H

1

[1.007 84, 1.008 11]

m

indium

In

49

114.818(1)

 

iodine

I

53

126.904 47(3)

 

iridium

Ir

77

192.217(3)

 

iron

Fe

26

55.845(2)

 

krypton

Kr

36

83.798(2)

g m

lanthanum

La

57

138.905 47(7)

g

lawrencium*

Lr

103

 

 

lead

Pb

82

207.2(1)

g r

lithium

Li

3

[6.938, 6.997]

m

livermorium*

Lv

116

 

 

lutetium

Lu

71

174.9668(1)

g

magnesium

Mg

12

[24.304, 24.307]

 

manganese

Mn

25

54.938 044(3)

 

meitnerium*

Mt

109

 

 

mendelevium*

Md

101

 

 

mercury

Hg

80

200.592(3)

 

molybdenum

Mo

42

95.95(1)

g

neodymium

Nd

60

144.242(3)

g

neon

Ne

10

20.1797(6)

g m

neptunium*

Np

93

 

 

nickel

Ni

28

58.6934(4)

r

niobium

Nb

41

92.906 37(2)

 

nitrogen

N

7

[14.006 43, 14.007 28]

 

nobelium*

No

102

 

 

osmium

Os

76

190.23(3)

g

oxygen

O

8

[15.999 03, 15.999 77]

 

palladium

Pd

46

106.42(1)

g

phosphorus

P

15

30.973 761 998(5)

 

platinum

Pt

78

195.084(9)

 

plutonium*

Pu

94

 

 

polonium*

Po

84

 

 

potassium

K

19

39.0983(1)

 

praseodymium

Pr

59

140.907 66(2)

 

promethium*

Pm

61

 

 

protactinium*

Pa

91

231.035 88(2)

 

radium*

Ra

88

 

 

radon*

Rn

86

 

 

roentgenium*

Rg

111

 

 

rhenium

Re

75

186.207(1)

 

rhodium

Rh

45

102.905 50(2)

 

rubidium

Rb

37

85.4678(3)

g

ruthenium

Ru

44

101.07(2)

g

rutherfordium*

Rf

104

 

 

samarium

Sm

62

150.36(2)

g

scandium

Sc

21

44.955 908(5)

 

seaborgium*

Sg

106

 

 

selenium

Se

34

78.971(8)

r

silicon

Si

14

[28.084, 28.086]

 

silver

Ag

47

107.8682(2)

g

sodium

Na

11

22.989 769 28(2)

 

strontium

Sr

38

87.62(1)

g r

sulfur

S

16

[32.059, 32.076]

 

tantalum

Ta

73

180.947 88(2)

 

technetium*

Tc

43

 

 

tellurium

Te

52

127.60(3)

g

terbium

Tb

65

158.925 35(2)

 

thallium

Tl

81

[204.382, 204.385]

 

thorium*

Th

90

232.0377(4)

g

thulium

Tm

69

168.934 22(2)

 

tin

Sn

50

118.710(7)

g

titanium

Ti

22

47.867(1)

 

tungsten

W

74

183.84(1)

 

ununoctium*

Uuo

118

 

 

ununpentium*

Uup

115

 

 

ununtrium*

Uut

113

 

 

uranium*

U

92

238.028 91(3)

g m

vanadium

V

23

50.9415(1)

 

xenon

Xe

54

131.293(6)

g m

ytterbium

Yb

70

173.054(5)

g

yttrium

Y

39

88.905 84(2)

 

zinc

Zn

30

65.38(2)

r

zirconium

Zr

40

91.224(2)

g

*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