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Current Table of Standard Atomic Weights in Order of Atomic Number

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, 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]. Figures in this report display distributions of atomic-weight variation for specified elements. 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.

Order of Atomic Number

Atomic Number

Name

Symbol

Standard Atomic Weight

Footnotes

1

hydrogen

H

[1.007 84, 1.008 11]

m

2

helium

He

4.002 602(2)

 g r

3

lithium

Li

[6.938, 6.997]

m

4

beryllium

Be

9.012 1831(5)

 

5

boron

B

[10.806, 10.821]

m

6

carbon

C

[12.0096, 12.0116]

 

7

nitrogen

N

[14.006 43, 14.007 28]

 

8

oxygen

O

[15.999 03, 15.999 77]

 

9

fluorine

F

18.998 403 163(6)

 

10

neon

Ne

20.1797(6)

g m

11

sodium

Na

22.989 769 28(2)

 

12

magnesium

Mg

[24.304, 24.307]

 

13

aluminium (aluminum)

Al

26.981 5385(7)

 

14

silicon

Si

[28.084, 28.086]

 

15

phosphorus

P

30.973 761 998(5)

 

16

sulfur

S

[32.059, 32.076]

 

17

chlorine

Cl

[35.446, 35.457]

m

18

argon

Ar

39.948(1)

g r

19

potassium

K

39.0983(1)

 

20

calcium

Ca

40.078(4)

g

21

scandium

Sc

44.955 908(5)

 

22

titanium

Ti

47.867(1)

 

23

vanadium

V

50.9415(1)

 

24

chromium

Cr

51.9961(6)

 

25

manganese

Mn

54.938 044(3)

 

26

iron

Fe

55.845(2)

 

27

cobalt

Co

58.933 194(4)

 

28

nickel

Ni

58.6934(4)

r

29

copper

Cu

63.546(3)

r

30

zinc

Zn

65.38(2)

r

31

gallium

Ga

69.723(1)

 

32

germanium

Ge

72.630(8)

 

33

arsenic

As

74.921 595(6)

 

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

85.4678(3)

g

38

strontium

Sr

87.62(1)

g r

39

yttrium

Y

88.905 84(2)

 

40

zirconium

Zr

91.224(2)

g

41

niobium

Nb

92.906 37(2)

 

42

molybdenum

Mo

95.95(1)

g

43

technetium*

Tc

 

 

44

ruthenium

Ru

101.07(2)

g

45

rhodium

Rh

102.905 50(2)

 

46

palladium

Pd

106.42(1)

g

47

silver

Ag

107.8682(2)

g

48

cadmium

Cd

112.414(4)

g

49

indium

In

114.818(1)

 

50

tin

Sn

118.710(7)

g

51

antimony

Sb

121.760(1)

g

52

tellurium

Te

127.60(3)

g

53

iodine

I

126.904 47(3)

 

54

xenon

Xe

131.293(6)

g m

55

caesium (cesium)

Cs

132.905 451 96(6)

 

56

barium

Ba

137.327(7)

 

57

lanthanum

La

138.905 47(7)

g

58

cerium

Ce

140.116(1)

g

59

praseodymium

Pr

140.907 66(2)

 

60

neodymium

Nd

144.242(3)

g

61

promethium*

Pm

 

 

62

samarium

Sm

150.36(2)

g

63

europium

Eu

151.964(1)

g

64

gadolinium

Gd

157.25(3)

g

65

terbium

Tb

158.925 35(2)

 

66

dysprosium

Dy

162.500(1)

g

67

holmium

Ho

164.930 33(2)

 

68

erbium

Er

167.259(3)

g

69

thulium

Tm

168.934 22(2)

 

70

ytterbium

Yb

173.054(5)

g

71

lutetium

Lu

174.9668(1)

g

72

hafnium

Hf

178.49(2)

 

73

tantalum

Ta

180.947 88(2)

 

74

tungsten

W

183.84(1)

 

75

rhenium

Re

186.207(1)

 

76

osmium

Os

190.23(3)

g

77

iridium

Ir

192.217(3)

 

78

platinum

Pt

195.084(9)

 

79

gold

Au

196.966 569(5)

 

80

mercury

Hg

200.592(3)

 

81

thallium

Tl

[204.382, 204.385]

 

82

lead

Pb

207.2(1)

g r

83

bismuth

Bi

208.980 40(1)

 

84

polonium*

Po

 

 

85

astatine*

At

 

 

86

radon*

Rn

 

 

87

francium*

Fr

 

 

88

radium*

Ra

 

 

89

actinium*

Ac

 

 

90

thorium*

Th

232.0377(4)

g

91

protactinium*

Pa

231.035 88(2)

 

92

uranium*

U

238.028 91(3)

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