Visualization

84elements with a standard atomic weight
14given as an interval
34without a standard atomic weight
689values recommended since 1902
289isotopes with an abundance

Standard atomic weights

Relative uncertainty
Year of the current value
Values since 1902

Relative uncertainty of the standard atomic weight

below 10⁻⁸
10⁻⁸ to 10⁻⁷
10⁻⁷ to 10⁻⁶
10⁻⁶ to 10⁻⁵
10⁻⁵ to 10⁻⁴
10⁻⁴ and above
no standard atomic weight

Year in which the current value was recommended

1969 and before
1970 to 1989
1990 to 2004
2005 to 2012
2013 to 2018
2019 to 2024
no standard atomic weight

Number of values recommended since 1902

1 to 4
5 or 6
7
8
9 or 10
11 to 13
no standard atomic weight

Hydrogen H, Z = 1

[1.007 84, 1.008 11]

Standard atomic weight, given as an interval. Relative uncertainty 2.7 × 10^-4.

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

issued 2009, doi:10.1351/PAC-REP-10-09-14

10 values recommended since 1902

Year	Value	Report
2009	[1.007 84, 1.008 11]	doi:10.1351/PAC-REP-10-09-14
1981	1.007 94(7)	doi:10.1351/pac198355071101
1971	1.0079(1)	doi:10.1351/pac197230030637
1969	1.0080(3)	doi:10.1351/pac197021010091
1961	1.007 97(1)	doi:10.1021/ja00881a001
1940	1.0080	doi:10.1039/JR9400000475
1938	1.0081	doi:10.1039/JR9380001101
1931	1.0078	doi:10.1039/JR9310001617
1903	1.008	doi:10.1021/ja02003a001
1902	1.01	doi:10.1007/BF01370337

2 isotopes with an abundance

¹H²H

Isotope	Amount fraction
¹H	[0.999 72, 0.999 99]
²H	[0.000 01, 0.000 28]

Helium He, Z = 2

4.002 602(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 10.0 × 10^-7.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.
r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.

issued 1983, doi:10.1351/pac198456060653

8 values recommended since 1902

Year	Value	Report
1983	4.002 602(2)	doi:10.1351/pac198456060653
1969	4.002 60(1)	doi:10.1351/pac197021010091
1961	4.0026	doi:10.1021/ja00881a001
1938	4.003	doi:10.1039/JR9380001101
1931	4.002	doi:10.1039/JR9310001617
1916	4	doi:10.1021/ja02176a001
1911	3.99	doi:10.1021/ja01928a001
1902	4	doi:10.1007/BF01370337

2 isotopes with an abundance

³He⁴He

Isotope	Amount fraction
³He	0.000 002(2)
⁴He	0.999 998(2)

Lithium Li, Z = 3

[6.938, 6.997]

Standard atomic weight, given as an interval. Relative uncertainty 8.5 × 10^-3.

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

issued 2009, doi:10.1351/PAC-REP-10-09-14

8 values recommended since 1902

Year	Value	Report
2009	[6.938, 6.997]	doi:10.1351/PAC-REP-10-09-14
1983	6.941(2)	doi:10.1351/pac198456060653
1969	6.941(3)	doi:10.1351/pac197021010091
1961	6.939	doi:10.1021/ja00881a001
1925	6.940	doi:10.1039/CT9252700913
1911	6.94	doi:10.1021/ja01928a001
1909	7	doi:10.1021/ja01931a001
1902	7.03	doi:10.1007/BF01370337

2 isotopes with an abundance

⁶Li⁷Li

Isotope	Amount fraction
⁶Li	[0.019, 0.078]
⁷Li	[0.922, 0.981]

Beryllium Be, Z = 4

9.012 1831(5)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.1 × 10^-7.

issued 2013, doi:10.1515/pac-2015-0305

7 values recommended since 1902

Year	Value	Report
2013	9.012 1831(5)	doi:10.1515/pac-2015-0305
1985	9.012 182(3)	doi:10.1351/pac198658121677
1969	9.012 18(1)	doi:10.1351/pac197021010091
1961	9.0122	doi:10.1021/ja00881a001
1949	9.013	doi:10.1039/JR9510000001
1925	9.02	doi:10.1039/CT9252700913
1902	9.1	doi:10.1007/BF01370337

1 isotope with an abundance

⁹Be

Isotope	Amount fraction
⁹Be	1

Boron B, Z = 5

[10.806, 10.821]

Standard atomic weight, given as an interval. Relative uncertainty 1.4 × 10^-3.

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

issued 2009, doi:10.1351/PAC-REP-10-09-14

8 values recommended since 1902

Year	Value	Report
2009	[10.806, 10.821]	doi:10.1351/PAC-REP-10-09-14
1995	10.811(7)	doi:10.1351/pac199668122339
1983	10.811(5)	doi:10.1351/pac198456060653
1969	10.81(1)	doi:10.1351/pac197021010091
1961	10.811(3)	doi:10.1021/ja00881a001
1925	10.82	doi:10.1039/CT9252700913
1920	10.9	doi:10.1021/ja02233a600
1902	11	doi:10.1007/BF01370337

2 isotopes with an abundance

¹⁰B¹¹B

Isotope	Amount fraction
¹⁰B	[0.189, 0.204]
¹¹B	[0.796, 0.811]

Carbon C, Z = 6

[12.0096, 12.0116]

Standard atomic weight, given as an interval. Relative uncertainty 1.7 × 10^-4.

issued 2009, doi:10.1351/PAC-REP-10-09-14

11 values recommended since 1902

Year	Value	Report
2009	[12.0096, 12.0116]	doi:10.1351/PAC-REP-10-09-14
1995	12.0107(8)	doi:10.1351/pac199668122339
1969	12.011(1)	doi:10.1351/pac197021010091
1961	12.011 15(5)	doi:10.1021/ja00881a001
1953	12.011	doi:10.1039/JR9540004713
1938	12.010	doi:10.1039/JR9380001101
1937	12.01	doi:10.1039/JR9370001900
1931	12	doi:10.1039/JR9310001617
1925	12	doi:10.1039/CT9252700913
1916	12.005	doi:10.1021/ja02176a001
1902	12	doi:10.1007/BF01370337

2 isotopes with an abundance

¹²C¹³C

Isotope	Amount fraction
¹²C	[0.9884, 0.9904]
¹³C	[0.0096, 0.0116]

Nitrogen N, Z = 7

[14.006 43, 14.007 28]

Standard atomic weight, given as an interval. Relative uncertainty 6.1 × 10^-5.

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

issued 2009, doi:10.1351/PAC-REP-10-09-14

8 values recommended since 1902

Year	Value	Report
2009	[14.006 43, 14.007 28]	doi:10.1351/PAC-REP-10-09-14
1999	14.0067(2)	doi:10.1351/pac200173040667
1985	14.006 74(7)	doi:10.1351/pac198658121677
1969	14.0067(1)	doi:10.1351/pac197021010091
1961	14.0067	doi:10.1021/ja00881a001
1920	14.008	doi:10.1021/ja02233a600
1907	14.01	doi:10.1021/ja01956a001
1902	14.04	doi:10.1007/BF01370337

2 isotopes with an abundance

¹⁴N¹⁵N

Isotope	Amount fraction
¹⁴N	[0.995 78, 0.996 63]
¹⁵N	[0.003 37, 0.004 22]

Oxygen O, Z = 8

[15.999 03, 15.999 77]

Standard atomic weight, given as an interval. Relative uncertainty 4.6 × 10^-5.

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

issued 2009, doi:10.1351/PAC-REP-10-09-14

4 values recommended since 1902

Year	Value	Report
2009	[15.999 03, 15.999 77]	doi:10.1351/PAC-REP-10-09-14
1969	15.9994(3)	doi:10.1351/pac197021010091
1961	15.9994(1)	doi:10.1021/ja00881a001
1902	16	doi:10.1007/BF01370337

3 isotopes with an abundance

¹⁶O¹⁷O¹⁸O

Isotope	Amount fraction
¹⁶O	[0.997 38, 0.997 76]
¹⁷O	[0.000 367, 0.000 400]
¹⁸O	[0.001 87, 0.002 22]

Fluorine F, Z = 9

18.998 403 162(5)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 5.3 × 10^-10.

issued 2021, doi:10.1515/pac-2019-0603

10 values recommended since 1902

Year	Value	Report
2021	18.998 403 162(5)	doi:10.1515/pac-2019-0603
2013	18.998 403 163(6)	doi:10.1515/pac-2015-0305
1995	18.998 4032(5)	doi:10.1351/pac199668122339
1985	18.998 4032(9)	doi:10.1351/pac198658121677
1975	18.998 403(1)	doi:10.1351/pac197647010075
1971	18.998 40(1)	doi:10.1351/pac197230030637
1969	18.9984(1)	doi:10.1351/pac197021010091
1961	18.9984	doi:10.1021/ja00881a001
1925	19	doi:10.1039/CT9252700913
1902	19	doi:10.1007/BF01370337

1 isotope with an abundance

¹⁹F

Isotope	Amount fraction
¹⁹F	1

Neon Ne, Z = 10

20.1797(6)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 5.9 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.
m Modified isotopic compositions may be found in commercially available material because the material has been subjected to some undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.

issued 1985, doi:10.1351/pac198658121677

7 values recommended since 1902

Year	Value	Report
1985	20.1797(6)	doi:10.1351/pac198658121677
1979	20.179(1)	doi:10.1351/pac198052102349
1967	20.179(3)	doi:10.1351/pac196918040569
1931	20.183	doi:10.1039/JR9310001617
1911	20.2	doi:10.1021/ja01928a001
1909	20	doi:10.1021/ja01931a001
1902	20	doi:10.1007/BF01370337

3 isotopes with an abundance

²⁰Ne²¹Ne²²Ne

Isotope	Amount fraction
²⁰Ne	0.9048(3)
²¹Ne	0.0027(1)
²²Ne	0.0925(3)

Sodium Na, Z = 11

22.989 769 28(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.7 × 10^-9.

issued 2005, doi:10.1351/pac200678112051

10 values recommended since 1902

Year	Value	Report
2005	22.989 769 28(2)	doi:10.1351/pac200678112051
1995	22.989 770(2)	doi:10.1351/pac199668122339
1985	22.989 768(6)	doi:10.1351/pac198658121677
1971	22.989 77(1)	doi:10.1351/pac197230030637
1969	22.9898(1)	doi:10.1351/pac197021010091
1961	22.9898	doi:10.1021/ja00881a001
1953	22.991	doi:10.1039/JR9540004713
1925	22.997	doi:10.1039/CT9252700913
1909	23	doi:10.1021/ja01931a001
1902	23.05	doi:10.1007/BF01370337

1 isotope with an abundance

²³Na

Isotope	Amount fraction
²³Na	1

Magnesium Mg, Z = 12

[24.304, 24.307]

Standard atomic weight, given as an interval. Relative uncertainty 1.2 × 10^-4.

issued 2011, doi:10.1351/PAC-REP-13-03-02

7 values recommended since 1902

Year	Value	Report
2011	[24.304, 24.307]	doi:10.1351/PAC-REP-13-03-02
1985	24.3050(6)	doi:10.1351/pac198658121677
1969	24.305(1)	doi:10.1351/pac197021010091
1967	24.305	doi:10.1351/pac196918040569
1961	24.312	doi:10.1021/ja00881a001
1909	24.32	doi:10.1021/ja01931a001
1902	24.36	doi:10.1007/BF01370337

3 isotopes with an abundance

²⁴Mg²⁵Mg²⁶Mg

Isotope	Amount fraction
²⁴Mg	[0.7888, 0.7905]
²⁵Mg	[0.099 88, 0.100 34]
²⁶Mg	[0.1096, 0.1109]

Aluminium Al, Z = 13

26.981 5384(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.2 × 10^-8.

issued 2017, doi:10.1515/pac-2019-0603

12 values recommended since 1902

Year	Value	Report
2017	26.981 5384(3)	doi:10.1515/pac-2019-0603
2013	26.981 5385(7)	doi:10.1515/pac-2015-0305
2005	26.981 5386(8)	doi:10.1351/pac200678112051
1995	26.981 538(2)	doi:10.1351/pac199668122339
1985	26.981 539(5)	doi:10.1351/pac198658121677
1971	26.981 54(1)	doi:10.1351/pac197230030637
1969	28.9815(1)	doi:10.1351/pac197021010091
1961	26.9815	doi:10.1021/ja00881a001
1951	26.98	doi:10.1039/JR9530000001
1925	26.97	doi:10.1039/CT9252700913
1922	27	doi:10.1021/ja01441a001
1902	27.1	doi:10.1007/BF01370337

1 isotope with an abundance

²⁷Al

Isotope	Amount fraction
²⁷Al	1

Silicon Si, Z = 14

[28.084, 28.086]

Standard atomic weight, given as an interval. Relative uncertainty 7.1 × 10^-5.

issued 2009, doi:10.1351/PAC-REP-10-09-14

9 values recommended since 1902

Year	Value	Report
2009	[28.084, 28.086]	doi:10.1351/PAC-REP-10-09-14
1975	28.0855(3)	doi:10.1351/pac197647010075
1969	28.086(3)	doi:10.1351/pac197021010091
1961	28.086(1)	doi:10.1021/ja00881a001
1951	28.09	doi:10.1039/JR9530000001
1925	28.06	doi:10.1039/CT9252700913
1922	28.1	doi:10.1021/ja01441a001
1909	28.3	doi:10.1021/ja01931a001
1902	28.4	doi:10.1007/BF01370337

3 isotopes with an abundance

²⁸Si²⁹Si³⁰Si

Isotope	Amount fraction
²⁸Si	[0.921 91, 0.923 18]
²⁹Si	[0.046 45, 0.046 99]
³⁰Si	[0.030 37, 0.031 10]

Phosphorus P, Z = 15

30.973 761 998(5)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.2 × 10^-10.

issued 2013, doi:10.1515/pac-2015-0305

13 values recommended since 1902

Year	Value	Report
2013	30.973 761 998(5)	doi:10.1515/pac-2015-0305
2005	30.973 762(2)	doi:10.1351/pac200678112051
1995	30.973 761(2)	doi:10.1351/pac199668122339
1985	30.973 762(4)	doi:10.1351/pac198658121677
1971	30.973 76(1)	doi:10.1351/pac197230030637
1969	30.9738(1)	doi:10.1351/pac197021010091
1961	30.9738	doi:10.1021/ja00881a001
1951	30.975	doi:10.1039/JR9530000001
1939	30.98	doi:10.1039/JR9390000351
1931	31.02	doi:10.1039/JR9310001617
1925	31.027	doi:10.1039/CT9252700913
1911	31.04	doi:10.1021/ja01928a001
1902	31	doi:10.1007/BF01370337

1 isotope with an abundance

³¹P

Isotope	Amount fraction
³¹P	1

Sulfur S, Z = 16

[32.059, 32.076]

Standard atomic weight, given as an interval. Relative uncertainty 5.3 × 10^-4.

issued 2009, doi:10.1351/PAC-REP-10-09-14

12 values recommended since 1902

Year	Value	Report
2009	[32.059, 32.076]	doi:10.1351/PAC-REP-10-09-14
1999	32.065(5)	doi:10.1351/pac200173040667
1983	32.066(6)	doi:10.1351/pac198456060653
1969	32.06(1)	doi:10.1351/pac197021010091
1961	32.064(3)	doi:10.1021/ja00881a001
1951	32.066(3)	doi:10.1039/JR9530000001
1947	32.066	doi:10.1039/JR9510000001
1931	32.06	doi:10.1039/JR9310001617
1925	32.064	doi:10.1039/CT9252700913
1916	32.06	doi:10.1021/ja02176a001
1909	32.07	doi:10.1021/ja01931a001
1902	32.06	doi:10.1007/BF01370337

4 isotopes with an abundance

³²S³³S³⁴S³⁶S

Isotope	Amount fraction
³²S	[0.9441, 0.9529]
³³S	[0.007 29, 0.007 97]
³⁴S	[0.0396, 0.0477]
³⁶S	[0.000 129, 0.000 187]

Chlorine Cl, Z = 17

[35.446, 35.457]

Standard atomic weight, given as an interval. Relative uncertainty 3.1 × 10^-4.

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

issued 2009, doi:10.1351/PAC-REP-10-09-14

7 values recommended since 1902

Year	Value	Report
2009	[35.446, 35.457]	doi:10.1351/PAC-REP-10-09-14
1999	35.453(2)	doi:10.1351/pac200173040667
1985	35.4527(9)	doi:10.1351/pac198658121677
1961	35.453(1)	doi:10.1021/ja00881a001
1925	35.457	doi:10.1039/CT9252700913
1909	35.46	doi:10.1021/ja01931a001
1902	35.45	doi:10.1007/BF01370337

2 isotopes with an abundance

³⁵Cl³⁷Cl

Isotope	Amount fraction
³⁵Cl	[0.755, 0.761]
³⁷Cl	[0.239, 0.245]

Argon Ar, Z = 18

[39.792, 39.963]

Standard atomic weight, given as an interval. Relative uncertainty 4.3 × 10^-3.

issued 2017, doi:10.1515/pac-2019-0603

9 values recommended since 1902

Year	Value	Report
2017	[39.792, 39.963]	doi:10.1515/pac-2019-0603
1979	39.948(1)	doi:10.1351/pac198052102349
1969	39.948(3)	doi:10.1351/pac197021010091
1961	39.948	doi:10.1021/ja00881a001
1931	39.944	doi:10.1039/JR9310001617
1925	39.91	doi:10.1039/CT9252700913
1920	39.9	doi:10.1021/ja02233a600
1911	39.88	doi:10.1021/ja01928a001
1902	39.9	doi:10.1007/BF01370337

3 isotopes with an abundance

³⁶Ar³⁸Ar⁴⁰Ar

Isotope	Amount fraction
³⁶Ar	[0.0000, 0.0207]
³⁸Ar	[0.000, 0.043]
⁴⁰Ar	[0.936, 1.000]

Potassium K, Z = 19

39.0983(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 5.1 × 10^-6.

issued 1979, doi:10.1351/pac198052102349

11 values recommended since 1902

Year	Value	Report
1979	39.0983(1)	doi:10.1351/pac198052102349
1975	39.0983(3)	doi:10.1351/pac197647010075
1971	39.098(3)	doi:10.1351/pac197230030637
1969	39.102(3)	doi:10.1351/pac197021010091
1961	39.102	doi:10.1021/ja00881a001
1951	39.100	doi:10.1039/JR9530000001
1934	39.096	doi:10.1039/JR9340000499
1931	39.10	doi:10.1039/JR9310001617
1925	39.096	doi:10.1039/CT9252700913
1909	39.10	doi:10.1021/ja01931a001
1902	39.15	doi:10.1007/BF01370337

3 isotopes with an abundance

³⁹K⁴⁰K⁴¹K

Isotope	Amount fraction
³⁹K	0.932 581(44)
⁴⁰K	0.000 117(1)
⁴¹K	0.067 302(44)

Calcium Ca, Z = 20

40.078(4)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.0 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1983, doi:10.1351/pac198456060653

6 values recommended since 1902

Year	Value	Report
1983	40.078(4)	doi:10.1351/pac198456060653
1969	40.08(1)	doi:10.1351/pac197021010091
1931	40.08	doi:10.1039/JR9310001617
1912	40.07	doi:10.1021/ja02224a601
1909	40.09	doi:10.1021/ja01931a001
1902	40.1	doi:10.1007/BF01370337

6 isotopes with an abundance

⁴⁰Ca⁴²Ca⁴³Ca⁴⁴Ca⁴⁶Ca⁴⁸Ca

Isotope	Amount fraction
⁴⁰Ca	0.969 41(156)
⁴²Ca	0.006 47(23)
⁴³Ca	0.001 35(10)
⁴⁴Ca	0.020 86(110)
⁴⁶Ca	0.000 04(3)
⁴⁸Ca	0.001 87(21)

Scandium Sc, Z = 21

44.955 907(4)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.8 × 10^-7.

issued 2021, doi:10.1515/pac-2019-0603

12 values recommended since 1902

Year	Value	Report
2021	44.955 907(4)	doi:10.1515/pac-2019-0603
2013	44.955 908(5)	doi:10.1515/pac-2015-0305
2005	44.955 912(6)	doi:10.1351/pac200678112051
1995	44.955 910(8)	doi:10.1351/pac199668122339
1985	44.955 910(9)	doi:10.1351/pac198658121677
1983	44.955 91(1)	doi:10.1351/pac198456060653
1969	44.9559(1)	doi:10.1351/pac197021010091
1961	44.956	doi:10.1021/ja00881a001
1951	44.96	doi:10.1039/JR9530000001
1925	45.10	doi:10.1039/CT9252700913
1921	45.1	doi:10.1021/ja01454a600
1902	44.1	doi:10.1007/BF01370337

1 isotope with an abundance

⁴⁵Sc

Isotope	Amount fraction
⁴⁵Sc	1

Titanium Ti, Z = 22

47.867(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.2 × 10^-5.

issued 1993, doi:10.1351/pac199466122423

5 values recommended since 1902

Year	Value	Report
1993	47.867(1)	doi:10.1351/pac199466122423
1979	47.88(3)	doi:10.1351/pac198052102349
1969	47.90(3)	doi:10.1351/pac197021010091
1931	47.90	doi:10.1039/JR9310001617
1902	48.1	doi:10.1007/BF01370337

5 isotopes with an abundance

⁴⁶Ti⁴⁷Ti⁴⁸Ti⁴⁹Ti⁵⁰Ti

Isotope	Amount fraction
⁴⁶Ti	0.0825(3)
⁴⁷Ti	0.0744(2)
⁴⁸Ti	0.7372(3)
⁴⁹Ti	0.0541(2)
⁵⁰Ti	0.0518(2)

Vanadium V, Z = 23

50.9415(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.9 × 10^-6.

issued 1977, doi:10.1351/pac197951020405

8 values recommended since 1902

Year	Value	Report
1977	50.9415(1)	doi:10.1351/pac197951020405
1969	50.9414(3)	doi:10.1351/pac197021010091
1961	50.942	doi:10.1021/ja00881a001
1931	50.95	doi:10.1039/JR9310001617
1925	50.96	doi:10.1039/CT9252700913
1912	51	doi:10.1021/ja02224a601
1911	51.06	doi:10.1021/ja01928a001
1902	51.2	doi:10.1007/BF01370337

2 isotopes with an abundance

⁵⁰V⁵¹V

Isotope	Amount fraction
⁵⁰V	0.002 50(10)
⁵¹V	0.997 50(10)

Chromium Cr, Z = 24

51.9961(6)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.3 × 10^-5.

issued 1983, doi:10.1351/pac198456060653

7 values recommended since 1902

Year	Value	Report
1983	51.9961(6)	doi:10.1351/pac198456060653
1969	51.996(1)	doi:10.1351/pac197021010091
1967	51.996	doi:10.1351/pac196918040569
1961	51.996(1)	doi:10.1021/ja00881a001
1925	52.01	doi:10.1039/CT9252700913
1910	52	doi:10.1021/ja01919a001
1902	52.1	doi:10.1007/BF01370337

4 isotopes with an abundance

⁵⁰Cr⁵²Cr⁵³Cr⁵⁴Cr

Isotope	Amount fraction
⁵⁰Cr	0.043 45(13)
⁵²Cr	0.837 89(18)
⁵³Cr	0.095 01(17)
⁵⁴Cr	0.023 65(7)

Manganese Mn, Z = 25

54.938 043(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 7.3 × 10^-8.

issued 2017, doi:10.1515/pac-2019-0603

10 values recommended since 1902

Year	Value	Report
2017	54.938 043(2)	doi:10.1515/pac-2019-0603
2013	54.938 044(3)	doi:10.1515/pac-2015-0305
2005	54.938 045(5)	doi:10.1351/pac200678112051
1995	54.938 049(9)	doi:10.1351/pac199668122339
1985	54.938 05(1)	doi:10.1351/pac198658121677
1969	54.9380(1)	doi:10.1351/pac197021010091
1961	54.9380	doi:10.1021/ja00881a001
1953	54.94	doi:10.1039/JR9540004713
1909	54.93	doi:10.1021/ja01931a001
1902	55	doi:10.1007/BF01370337

1 isotope with an abundance

⁵⁵Mn

Isotope	Amount fraction
⁵⁵Mn	1

Iron Fe, Z = 26

55.845(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 7.2 × 10^-5.

issued 1993, doi:10.1351/pac199466122423

6 values recommended since 1902

Year	Value	Report
1993	55.845(2)	doi:10.1351/pac199466122423
1961	55.847(3)	doi:10.1021/ja00881a001
1940	55.85	doi:10.1039/JR9400000475
1912	55.84	doi:10.1021/ja02224a601
1909	55.85	doi:10.1021/ja01931a001
1902	55.9	doi:10.1007/BF01370337

4 isotopes with an abundance

⁵⁴Fe⁵⁶Fe⁵⁷Fe⁵⁸Fe

Isotope	Amount fraction
⁵⁴Fe	0.058 45(105)
⁵⁶Fe	0.917 54(106)
⁵⁷Fe	0.021 19(29)
⁵⁸Fe	0.002 82(12)

Cobalt Co, Z = 27

58.933 194(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.0 × 10^-7.

issued 2017, doi:10.1515/pac-2019-0603

10 values recommended since 1902

Year	Value	Report
2017	58.933 194(3)	doi:10.1515/pac-2019-0603
2013	58.933 194(4)	doi:10.1515/pac-2015-0305
2005	58.933 195(5)	doi:10.1351/pac200678112051
1995	58.933 200(9)	doi:10.1351/pac199668122339
1985	58.933 20(1)	doi:10.1351/pac198658121677
1969	58.9332(1)	doi:10.1351/pac197021010091
1961	58.9332	doi:10.1021/ja00881a001
1925	58.94	doi:10.1039/CT9252700913
1909	58.97	doi:10.1021/ja01931a001
1902	59	doi:10.1007/BF01370337

1 isotope with an abundance

⁵⁹Co

Isotope	Amount fraction
⁵⁹Co	1

Nickel Ni, Z = 28

58.6934(4)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.4 × 10^-5.

r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.

issued 2007, doi:10.1351/PAC-REP-09-08-03

9 values recommended since 1902

Year	Value	Report
2007	58.6934(4)	doi:10.1351/PAC-REP-09-08-03
1989	58.6934(2)	doi:10.1351/pac199163070975
1979	58.69(1)	doi:10.1351/pac198052102349
1973	58.70(1)	doi:10.1351/pac197437040589
1969	58.71(3)	doi:10.1351/pac197021010091
1955	58.71	doi:10.1021/ja01595a001
1925	58.69	doi:10.1039/CT9252700913
1909	58.68	doi:10.1021/ja01931a001
1902	58.7	doi:10.1007/BF01370337

5 isotopes with an abundance

⁵⁸Ni⁶⁰Ni⁶¹Ni⁶²Ni⁶⁴Ni

Isotope	Amount fraction
⁵⁸Ni	0.680 769(190)
⁶⁰Ni	0.262 231(150)
⁶¹Ni	0.011 399(13)
⁶²Ni	0.036 345(40)
⁶⁴Ni	0.009 256(19)

Copper Cu, Z = 29

63.546(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 9.4 × 10^-5.

r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.

issued 1969, doi:10.1351/pac197021010091

5 values recommended since 1902

Year	Value	Report
1969	63.546(3)	doi:10.1351/pac197021010091
1965	63.546(1)	doi:10.1351/pac196918040569
1947	63.54	doi:10.1039/JR9510000001
1909	63.57	doi:10.1021/ja01931a001
1902	63.6	doi:10.1007/BF01370337

2 isotopes with an abundance

⁶³Cu⁶⁵Cu

Isotope	Amount fraction
⁶³Cu	0.6915(15)
⁶⁵Cu	0.3085(15)

Zinc Zn, Z = 30

65.38(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 6.1 × 10^-4.

r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.

issued 2007, doi:10.1351/PAC-REP-09-08-03

9 values recommended since 1902

Year	Value	Report
2007	65.38(2)	doi:10.1351/PAC-REP-09-08-03
2001	65.409(4)	doi:10.1351/pac200375081107
1983	65.39(2)	doi:10.1351/pac198456060653
1971	65.38(1)	doi:10.1351/pac197230030637
1969	65.37(3)	doi:10.1351/pac197021010091
1961	65.37	doi:10.1021/ja00881a001
1925	65.38	doi:10.1039/CT9252700913
1909	65.37	doi:10.1021/ja01931a001
1902	65.4	doi:10.1007/BF01370337

5 isotopes with an abundance

⁶⁴Zn⁶⁶Zn⁶⁷Zn⁶⁸Zn⁷⁰Zn

Isotope	Amount fraction
⁶⁴Zn	0.4917(75)
⁶⁶Zn	0.2773(98)
⁶⁷Zn	0.0404(16)
⁶⁸Zn	0.1845(63)
⁷⁰Zn	0.0061(10)

Gallium Ga, Z = 31

69.723(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.9 × 10^-5.

issued 1987, doi:10.1351/pac198860060841

7 values recommended since 1902

Year	Value	Report
1987	69.723(1)	doi:10.1351/pac198860060841
1983	69.723(4)	doi:10.1351/pac198456060653
1969	69.72(1)	doi:10.1351/pac197021010091
1925	69.72	doi:10.1039/CT9252700913
1920	70.1	doi:10.1021/ja02233a600
1909	69.9	doi:10.1021/ja01931a001
1902	70	doi:10.1007/BF01370337

2 isotopes with an abundance

⁶⁹Ga⁷¹Ga

Isotope	Amount fraction
⁶⁹Ga	0.601 08(50)
⁷¹Ga	0.398 92(50)

Germanium Ge, Z = 32

72.630(8)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.2 × 10^-4.

issued 2011, doi:10.1351/PAC-REP-13-03-02

9 values recommended since 1902

Year	Value	Report
2011	72.630(8)	doi:10.1351/PAC-REP-13-03-02
2009	72.63(1)	doi:10.1351/PAC-REP-10-09-14
1999	72.64(1)	doi:10.1351/pac200173040667
1985	72.61(2)	doi:10.1351/pac198658121677
1969	72.59(3)	doi:10.1351/pac197021010091
1961	72.59	doi:10.1021/ja00881a001
1925	72.60	doi:10.1039/CT9252700913
1903	72.5	doi:10.1021/ja02003a001
1902	72	doi:10.1007/BF01370337

5 isotopes with an abundance

⁷⁰Ge⁷²Ge⁷³Ge⁷⁴Ge⁷⁶Ge

Isotope	Amount fraction
⁷⁰Ge	0.2052(19)
⁷²Ge	0.2745(15)
⁷³Ge	0.0776(8)
⁷⁴Ge	0.3652(12)
⁷⁶Ge	0.0775(12)

Arsenic As, Z = 33

74.921 595(6)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.6 × 10^-7.

issued 2013, doi:10.1515/pac-2015-0305

9 values recommended since 1902

Year	Value	Report
2013	74.921 595(6)	doi:10.1515/pac-2015-0305
1995	74.921 60(2)	doi:10.1351/pac199668122339
1985	74.921 59(2)	doi:10.1351/pac198658121677
1969	74.9216(1)	doi:10.1351/pac197021010091
1961	74.9216	doi:10.1021/ja00881a001
1934	74.91	doi:10.1039/JR9340000499
1931	74.93	doi:10.1039/JR9310001617
1910	74.96	doi:10.1021/ja01919a001
1902	75	doi:10.1007/BF01370337

1 isotope with an abundance

⁷⁵As

Isotope	Amount fraction
⁷⁵As	1

Selenium Se, Z = 34

78.971(8)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.0 × 10^-4.

r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.

issued 2013, doi:10.1515/pac-2015-0305

5 values recommended since 1902

Year	Value	Report
2013	78.971(8)	doi:10.1515/pac-2015-0305
1969	78.96(3)	doi:10.1351/pac197021010091
1934	78.96	doi:10.1039/JR9340000499
1903	79.2	doi:10.1021/ja02003a001
1902	79.1	doi:10.1007/BF01370337

6 isotopes with an abundance

⁷⁴Se⁷⁶Se⁷⁷Se⁷⁸Se⁸⁰Se⁸²Se

Isotope	Amount fraction
⁷⁴Se	0.0086(3)
⁷⁶Se	0.0923(7)
⁷⁷Se	0.0760(7)
⁷⁸Se	0.2369(22)
⁸⁰Se	0.4980(36)
⁸²Se	0.0882(15)

Bromine Br, Z = 35

[79.901, 79.907]

Standard atomic weight, given as an interval. Relative uncertainty 7.5 × 10^-5.

issued 2011, doi:10.1351/PAC-REP-13-03-02

6 values recommended since 1902

Year	Value	Report
2011	[79.901, 79.907]	doi:10.1351/PAC-REP-13-03-02
1965	79.904(1)	doi:10.1351/pac196918040569
1961	79.909(2)	doi:10.1021/ja00881a001
1925	79.916	doi:10.1039/CT9252700913
1909	79.92	doi:10.1021/ja01931a001
1902	79.96	doi:10.1007/BF01370337

2 isotopes with an abundance

⁷⁹Br⁸¹Br

Isotope	Amount fraction
⁷⁹Br	[0.505, 0.508]
⁸¹Br	[0.492, 0.495]

Krypton Kr, Z = 36

83.798(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.8 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.
m Modified isotopic compositions may be found in commercially available material because the material has been subjected to some undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.

issued 2001, doi:10.1351/pac200375081107

8 values recommended since 1902

Year	Value	Report
2001	83.798(2)	doi:10.1351/pac200375081107
1969	83.80(1)	doi:10.1351/pac197021010091
1951	83.80	doi:10.1039/JR9530000001
1932	83.7	doi:10.1021/ja01343a001
1925	82.9	doi:10.1039/CT9252700913
1911	82.92	doi:10.1021/ja01928a001
1910	83	doi:10.1021/ja01919a001
1902	81.8	doi:10.1007/BF01370337

6 isotopes with an abundance

⁷⁸Kr⁸⁰Kr⁸²Kr⁸³Kr⁸⁴Kr⁸⁶Kr

Isotope	Amount fraction
⁷⁸Kr	0.003 55(3)
⁸⁰Kr	0.022 86(10)
⁸²Kr	0.115 93(31)
⁸³Kr	0.115 00(19)
⁸⁴Kr	0.569 87(15)
⁸⁶Kr	0.172 79(41)

Rubidium Rb, Z = 37

85.4678(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 7.0 × 10^-6.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1969, doi:10.1351/pac197021010091

7 values recommended since 1902

Year	Value	Report
1969	85.4678(3)	doi:10.1351/pac197021010091
1961	85.47	doi:10.1021/ja00881a001
1937	85.48	doi:10.1039/JR9370001900
1925	85.44	doi:10.1039/CT9252700913
1909	85.45	doi:10.1021/ja01931a001
1905	85.5	doi:10.1021/ja01979a001
1902	85.4	doi:10.1007/BF01370337

2 isotopes with an abundance

⁸⁵Rb⁸⁷Rb

Isotope	Amount fraction
⁸⁵Rb	0.7217(2)
⁸⁷Rb	0.2783(2)

Strontium Sr, Z = 38

87.62(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.3 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.
r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.

issued 1969, doi:10.1351/pac197021010091

5 values recommended since 1902

Year	Value	Report
1969	87.62(1)	doi:10.1351/pac197021010091
1961	87.62	doi:10.1021/ja00881a001
1911	87.63	doi:10.1021/ja01928a001
1909	87.62	doi:10.1021/ja01931a001
1902	87.6	doi:10.1007/BF01370337

4 isotopes with an abundance

⁸⁴Sr⁸⁶Sr⁸⁷Sr⁸⁸Sr

Isotope	Amount fraction
⁸⁴Sr	0.0056(2)
⁸⁶Sr	0.0986(20)
⁸⁷Sr	0.0700(20)
⁸⁸Sr	0.8258(35)

Yttrium Y, Z = 39

88.905 838(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.5 × 10^-8.

issued 2021, doi:10.1515/pac-2019-0603

11 values recommended since 1902

Year	Value	Report
2021	88.905 838(2)	doi:10.1515/pac-2019-0603
2017	88.905 84(1)	doi:10.1515/pac-2019-0603
2013	88.905 84(2)	doi:10.1515/pac-2015-0305
1985	88.905 85(2)	doi:10.1351/pac198658121677
1969	88.9059(1)	doi:10.1351/pac197021010091
1961	88.905	doi:10.1021/ja00881a001
1931	88.92	doi:10.1039/JR9310001617
1925	88.9	doi:10.1039/CT9252700913
1920	89.33	doi:10.1021/ja02233a600
1903	89	doi:10.1021/ja02003a001
1902	89	doi:10.1007/BF01370337

1 isotope with an abundance

⁸⁹Y

Isotope	Amount fraction
⁸⁹Y	1

Zirconium Zr, Z = 40

91.222(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 6.6 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2024

7 values recommended since 1902

Year	Value	Report
2024	91.222(3)
1983	91.224(2)	doi:10.1351/pac198456060653
1969	91.22(1)	doi:10.1351/pac197021010091
1931	91.22	doi:10.1039/JR9310001617
1925	91	doi:10.1039/CT9252700913
1903	90.6	doi:10.1021/ja02003a001
1902	90.7	doi:10.1007/BF01370337

5 isotopes with an abundance

⁹⁰Zr⁹¹Zr⁹²Zr⁹⁴Zr⁹⁶Zr

Isotope	Amount fraction
⁹⁰Zr	0.5147(6)
⁹¹Zr	0.1123(6)
⁹²Zr	0.1716(4)
⁹⁴Zr	0.1736(7)
⁹⁶Zr	0.0278(4)

Niobium Nb, Z = 41

92.906 37(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.2 × 10^-7.

issued 2017, doi:10.1515/pac-2019-0603

10 values recommended since 1902

Year	Value	Report
2017	92.906 37(1)	doi:10.1515/pac-2019-0603
2013	92.906 37(2)	doi:10.1515/pac-2015-0305
1985	92.906 38(2)	doi:10.1351/pac198658121677
1969	92.9064(1)	doi:10.1351/pac197021010091
1961	92.906	doi:10.1021/ja00881a001
1935	92.91	doi:10.1039/JR9350000788
1931	93.3	doi:10.1039/JR9310001617
1917	93.1	doi:10.1021/ja02268a001
1909	93.5	doi:10.1021/ja01931a001
1902	94	doi:10.1007/BF01370337

1 isotope with an abundance

⁹³Nb

Isotope	Amount fraction
⁹³Nb	1

Molybdenum Mo, Z = 42

95.95(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.1 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2013, doi:10.1515/pac-2015-0305

8 values recommended since 1902

Year	Value	Report
2013	95.95(1)	doi:10.1515/pac-2015-0305
2007	95.96(2)	doi:10.1351/PAC-REP-09-08-03
2001	95.94(2)	doi:10.1351/pac200375081107
1975	95.94(1)	doi:10.1351/pac197647010075
1969	95.94(3)	doi:10.1351/pac197021010091
1961	95.94	doi:10.1021/ja00881a001
1938	95.95	doi:10.1039/JR9380001101
1902	96	doi:10.1007/BF01370337

7 isotopes with an abundance

⁹²Mo⁹⁴Mo⁹⁵Mo⁹⁶Mo⁹⁷Mo⁹⁸Mo¹⁰⁰Mo

Isotope	Amount fraction
⁹²Mo	0.146 49(106)
⁹⁴Mo	0.091 87(33)
⁹⁵Mo	0.158 73(30)
⁹⁶Mo	0.166 73(8)
⁹⁷Mo	0.095 82(15)
⁹⁸Mo	0.242 92(80)
¹⁰⁰Mo	0.097 44(65)

Technetium Tc, Z = 43

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 97.

Ruthenium Ru, Z = 44

101.07(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.0 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1983, doi:10.1351/pac198456060653

5 values recommended since 1902

Year	Value	Report
1983	101.07(2)	doi:10.1351/pac198456060653
1969	101.07(3)	doi:10.1351/pac197021010091
1961	101.07	doi:10.1021/ja00881a001
1953	101.1	doi:10.1039/JR9540004713
1902	101.7	doi:10.1007/BF01370337

7 isotopes with an abundance

⁹⁶Ru⁹⁸Ru⁹⁹Ru¹⁰⁰Ru¹⁰¹Ru¹⁰²Ru¹⁰⁴Ru

Isotope	Amount fraction
⁹⁶Ru	0.0554(14)
⁹⁸Ru	0.0187(3)
⁹⁹Ru	0.1276(14)
¹⁰⁰Ru	0.1260(7)
¹⁰¹Ru	0.1706(2)
¹⁰²Ru	0.3155(14)
¹⁰⁴Ru	0.1862(27)

Rhodium Rh, Z = 45

102.905 49(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.9 × 10^-7.

issued 2017, doi:10.1515/pac-2019-0603

8 values recommended since 1902

Year	Value	Report
2017	102.905 49(2)	doi:10.1515/pac-2019-0603
1995	102.905 50(2)	doi:10.1351/pac199668122339
1985	102.905 50(3)	doi:10.1351/pac198658121677
1969	102.9055(1)	doi:10.1351/pac197021010091
1961	102.905	doi:10.1021/ja00881a001
1925	102.91	doi:10.1039/CT9252700913
1909	102.9	doi:10.1021/ja01931a001
1902	103	doi:10.1007/BF01370337

1 isotope with an abundance

¹⁰³Rh

Isotope	Amount fraction
¹⁰³Rh	1

Palladium Pd, Z = 46

106.42(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.9 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1979, doi:10.1351/pac198052102349

6 values recommended since 1902

Year	Value	Report
1979	106.42(1)	doi:10.1351/pac198052102349
1969	106.4(1)	doi:10.1351/pac197021010091
1955	106.4	doi:10.1021/ja01595a001
1909	106.7	doi:10.1021/ja01931a001
1903	106.5	doi:10.1021/ja02003a001
1902	106	doi:10.1007/BF01370337

6 isotopes with an abundance

¹⁰²Pd¹⁰⁴Pd¹⁰⁵Pd¹⁰⁶Pd¹⁰⁸Pd¹¹⁰Pd

Isotope	Amount fraction
¹⁰²Pd	0.0102(1)
¹⁰⁴Pd	0.1114(8)
¹⁰⁵Pd	0.2233(8)
¹⁰⁶Pd	0.2733(3)
¹⁰⁸Pd	0.2646(9)
¹¹⁰Pd	0.1172(9)

Silver Ag, Z = 47

107.8682(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.7 × 10^-6.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1985, doi:10.1351/pac198658121677

7 values recommended since 1902

Year	Value	Report
1985	107.8682(2)	doi:10.1351/pac198658121677
1981	107.8682(3)	doi:10.1351/pac198355071101
1965	107.868(1)	doi:10.1351/pac196918040569
1961	107.870(3)	doi:10.1021/ja00881a001
1925	107.880	doi:10.1039/CT9252700913
1909	107.88	doi:10.1021/ja01931a001
1902	107.93	doi:10.1007/BF01370337

2 isotopes with an abundance

¹⁰⁷Ag¹⁰⁹Ag

Isotope	Amount fraction
¹⁰⁷Ag	0.518 39(8)
¹⁰⁹Ag	0.481 61(8)

Cadmium Cd, Z = 48

112.414(4)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 7.1 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2013, doi:10.1515/pac-2015-0305

8 values recommended since 1902

Year	Value	Report
2013	112.414(4)	doi:10.1515/pac-2015-0305
1985	112.411(8)	doi:10.1351/pac198658121677
1975	112.41(1)	doi:10.1351/pac197647010075
1969	112.40(1)	doi:10.1351/pac197021010091
1961	112.40	doi:10.1021/ja00881a001
1925	112.41	doi:10.1039/CT9252700913
1909	112.40	doi:10.1021/ja01931a001
1902	112.4	doi:10.1007/BF01370337

8 isotopes with an abundance

¹⁰⁶Cd¹⁰⁸Cd¹¹⁰Cd¹¹¹Cd¹¹²Cd¹¹³Cd¹¹⁴Cd¹¹⁶Cd

Isotope	Amount fraction
¹⁰⁶Cd	0.012 45(22)
¹⁰⁸Cd	0.008 88(11)
¹¹⁰Cd	0.124 70(61)
¹¹¹Cd	0.127 95(12)
¹¹²Cd	0.241 09(7)
¹¹³Cd	0.122 27(7)
¹¹⁴Cd	0.287 54(81)
¹¹⁶Cd	0.075 12(54)

Indium In, Z = 49

114.818(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.7 × 10^-5.

issued 2011, doi:10.1351/PAC-REP-13-03-02

8 values recommended since 1902

Year	Value	Report
2011	114.818(1)	doi:10.1351/PAC-REP-13-03-02
1991	114.818(3)	doi:10.1351/pac199264101519
1969	114.82(1)	doi:10.1351/pac197021010091
1955	114.82	doi:10.1021/ja01595a001
1934	114.76	doi:10.1039/JR9340000499
1909	114.8	doi:10.1021/ja01931a001
1905	115	doi:10.1021/ja01979a001
1902	114	doi:10.1007/BF01370337

2 isotopes with an abundance

¹¹³In¹¹⁵In

Isotope	Amount fraction
¹¹³In	0.042 81(52)
¹¹⁵In	0.957 19(52)

Tin Sn, Z = 50

118.710(7)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.2 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1983, doi:10.1351/pac198456060653

7 values recommended since 1902

Year	Value	Report
1983	118.710(7)	doi:10.1351/pac198456060653
1969	118.69(3)	doi:10.1351/pac197021010091
1961	118.69	doi:10.1021/ja00881a001
1925	118.70	doi:10.1039/CT9252700913
1916	118.7	doi:10.1021/ja02176a001
1903	119	doi:10.1021/ja02003a001
1902	118.5	doi:10.1007/BF01370337

10 isotopes with an abundance

¹¹²Sn¹¹⁴Sn¹¹⁵Sn¹¹⁶Sn¹¹⁷Sn¹¹⁸Sn¹¹⁹Sn¹²⁰Sn¹²²Sn¹²⁴Sn

Isotope	Amount fraction
¹¹²Sn	0.0097(1)
¹¹⁴Sn	0.0066(1)
¹¹⁵Sn	0.0034(1)
¹¹⁶Sn	0.1454(9)
¹¹⁷Sn	0.0768(7)
¹¹⁸Sn	0.2422(9)
¹¹⁹Sn	0.0859(4)
¹²⁰Sn	0.3258(9)
¹²²Sn	0.0463(3)
¹²⁴Sn	0.0579(5)

Antimony Sb, Z = 51

121.760(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.6 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1993, doi:10.1351/pac199466122423

8 values recommended since 1902

Year	Value	Report
1993	121.760(1)	doi:10.1351/pac199466122423
1989	121.757(3)	doi:10.1351/pac199163070975
1969	121.75(3)	doi:10.1351/pac197021010091
1961	121.75	doi:10.1021/ja00881a001
1931	121.76	doi:10.1039/JR9310001617
1925	121.77	doi:10.1039/CT9252700913
1903	120.2	doi:10.1021/ja02003a001
1902	120	doi:10.1007/BF01370337

2 isotopes with an abundance

¹²¹Sb¹²³Sb

Isotope	Amount fraction
¹²¹Sb	0.5721(5)
¹²³Sb	0.4279(5)

Tellurium Te, Z = 52

127.60(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.7 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1969, doi:10.1351/pac197021010091

5 values recommended since 1902

Year	Value	Report
1969	127.60(3)	doi:10.1351/pac197021010091
1961	127.60	doi:10.1021/ja00881a001
1934	127.61	doi:10.1039/JR9340000499
1909	127.5	doi:10.1021/ja01931a001
1902	127.6	doi:10.1007/BF01370337

8 isotopes with an abundance

¹²⁰Te¹²²Te¹²³Te¹²⁴Te¹²⁵Te¹²⁶Te¹²⁸Te¹³⁰Te

Isotope	Amount fraction
¹²⁰Te	0.0009(1)
¹²²Te	0.0255(12)
¹²³Te	0.0089(3)
¹²⁴Te	0.0474(14)
¹²⁵Te	0.0707(15)
¹²⁶Te	0.1884(25)
¹²⁸Te	0.3174(8)
¹³⁰Te	0.3408(62)

Iodine I, Z = 53

126.904 47(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.7 × 10^-7.

issued 1985, doi:10.1351/pac198658121677

9 values recommended since 1902

Year	Value	Report
1985	126.904 47(3)	doi:10.1351/pac198658121677
1969	126.9045(1)	doi:10.1351/pac197021010091
1961	126.9044	doi:10.1021/ja00881a001
1951	126.91	doi:10.1039/JR9530000001
1933	126.92	doi:10.1039/JR9330000354
1925	126.932	doi:10.1039/CT9252700913
1909	126.92	doi:10.1021/ja01931a001
1905	126.97	doi:10.1021/ja01979a001
1902	126.85	doi:10.1007/BF01370337

1 isotope with an abundance

¹²⁷I

Isotope	Amount fraction
¹²⁷I	1

Xenon Xe, Z = 54

131.293(6)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 9.1 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.
m Modified isotopic compositions may be found in commercially available material because the material has been subjected to some undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.

issued 1999, doi:10.1351/pac200173040667

10 values recommended since 1902

Year	Value	Report
1999	131.293(6)	doi:10.1351/pac200173040667
1985	131.29(2)	doi:10.1351/pac198658121677
1979	131.29(3)	doi:10.1351/pac198052102349
1969	131.30(1)	doi:10.1351/pac197021010091
1955	131.30	doi:10.1021/ja01595a001
1932	131.3	doi:10.1021/ja01343a001
1911	130.2	doi:10.1021/ja01928a001
1910	130.7	doi:10.1021/ja01919a001
1909	128	doi:10.1021/ja01931a001
1902	128	doi:10.1007/BF01370337

9 isotopes with an abundance

¹²⁴Xe¹²⁶Xe¹²⁸Xe¹²⁹Xe¹³⁰Xe¹³¹Xe¹³²Xe¹³⁴Xe¹³⁶Xe

Isotope	Amount fraction
¹²⁴Xe	0.000 95(5)
¹²⁶Xe	0.000 89(3)
¹²⁸Xe	0.019 10(13)
¹²⁹Xe	0.264 01(138)
¹³⁰Xe	0.040 71(22)
¹³¹Xe	0.212 32(51)
¹³²Xe	0.269 09(55)
¹³⁴Xe	0.104 36(35)
¹³⁶Xe	0.088 57(72)

Caesium Cs, Z = 55

132.905 451 96(6)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 9.0 × 10^-10.

issued 2013, doi:10.1515/pac-2015-0305

11 values recommended since 1902

Year	Value	Report
2013	132.905 451 96(6)	doi:10.1515/pac-2015-0305
2005	132.905 4519(2)	doi:10.1351/pac200678112051
1995	132.905 45(2)	doi:10.1351/pac199668122339
1985	132.905 43(5)	doi:10.1351/pac198658121677
1971	132.9054(1)	doi:10.1351/pac197230030637
1969	132.9055(1)	doi:10.1351/pac197021010091
1961	132.905	doi:10.1021/ja00881a001
1934	132.91	doi:10.1039/JR9340000499
1909	132.81	doi:10.1021/ja01931a001
1904	132.9	doi:10.1021/ja01991a001
1902	133	doi:10.1007/BF01370337

1 isotope with an abundance

¹³³Cs

Isotope	Amount fraction
¹³³Cs	1

Barium Ba, Z = 56

137.327(7)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.0 × 10^-4.

issued 1985, doi:10.1351/pac198658121677

7 values recommended since 1902

Year	Value	Report
1985	137.327(7)	doi:10.1351/pac198658121677
1975	137.33(1)	doi:10.1351/pac197647010075
1969	137.34(3)	doi:10.1351/pac197021010091
1961	137.34	doi:10.1021/ja00881a001
1931	137.36	doi:10.1039/JR9310001617
1909	137.37	doi:10.1021/ja01931a001
1902	137.4	doi:10.1007/BF01370337

7 isotopes with an abundance

¹³⁰Ba¹³²Ba¹³⁴Ba¹³⁵Ba¹³⁶Ba¹³⁷Ba¹³⁸Ba

Isotope	Amount fraction
¹³⁰Ba	0.0011(1)
¹³²Ba	0.0010(1)
¹³⁴Ba	0.0242(15)
¹³⁵Ba	0.0659(10)
¹³⁶Ba	0.0785(24)
¹³⁷Ba	0.1123(23)
¹³⁸Ba	0.7170(29)

Lanthanum La, Z = 57

138.905 47(7)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.0 × 10^-6.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2005, doi:10.1351/pac200678112051

9 values recommended since 1902

Year	Value	Report
2005	138.905 47(7)	doi:10.1351/pac200678112051
1985	138.9055(2)	doi:10.1351/pac198658121677
1969	138.9055(3)	doi:10.1351/pac197021010091
1961	138.91	doi:10.1021/ja00881a001
1933	138.92	doi:10.1039/JR9330000354
1925	138.90	doi:10.1039/CT9252700913
1909	139	doi:10.1021/ja01931a001
1903	138.9	doi:10.1021/ja02003a001
1902	138	doi:10.1007/BF01370337

2 isotopes with an abundance

¹³⁸La¹³⁹La

Isotope	Amount fraction
¹³⁸La	0.000 8881(71)
¹³⁹La	0.999 1119(71)

Cerium Ce, Z = 58

140.116(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.4 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1995, doi:10.1351/pac199668122339

7 values recommended since 1902

Year	Value	Report
1995	140.116(1)	doi:10.1351/pac199668122339
1985	140.115(4)	doi:10.1351/pac198658121677
1969	140.12(1)	doi:10.1351/pac197021010091
1961	140.12	doi:10.1021/ja00881a001
1931	140.13	doi:10.1039/JR9310001617
1904	140.25	doi:10.1021/ja01991a001
1902	140	doi:10.1007/BF01370337

4 isotopes with an abundance

¹³⁶Ce¹³⁸Ce¹⁴⁰Ce¹⁴²Ce

Isotope	Amount fraction
¹³⁶Ce	0.001 85(2)
¹³⁸Ce	0.002 51(2)
¹⁴⁰Ce	0.884 50(51)
¹⁴²Ce	0.111 14(51)

Praseodymium Pr, Z = 59

140.907 66(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.4 × 10^-7.

issued 2017, doi:10.1515/pac-2019-0603

9 values recommended since 1902

Year	Value	Report
2017	140.907 66(1)	doi:10.1515/pac-2019-0603
2013	140.907 66(2)	doi:10.1515/pac-2015-0305
1995	140.907 65(2)	doi:10.1351/pac199668122339
1985	140.907 65(3)	doi:10.1351/pac198658121677
1969	140.9077(1)	doi:10.1351/pac197021010091
1961	140.907	doi:10.1021/ja00881a001
1925	140.92	doi:10.1039/CT9252700913
1916	140.9	doi:10.1021/ja02176a001
1902	140.6	doi:10.1007/BF01370337

1 isotope with an abundance

¹⁴¹Pr

Isotope	Amount fraction
¹⁴¹Pr	1

Neodymium Nd, Z = 60

144.242(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.2 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2005, doi:10.1351/pac200678112051

6 values recommended since 1902

Year	Value	Report
2005	144.242(3)	doi:10.1351/pac200678112051
1969	144.24(3)	doi:10.1351/pac197021010091
1961	144.24	doi:10.1021/ja00881a001
1925	144.27	doi:10.1039/CT9252700913
1909	144.3	doi:10.1021/ja01931a001
1902	143.6	doi:10.1007/BF01370337

7 isotopes with an abundance

¹⁴²Nd¹⁴³Nd¹⁴⁴Nd¹⁴⁵Nd¹⁴⁶Nd¹⁴⁸Nd¹⁵⁰Nd

Isotope	Amount fraction
¹⁴²Nd	0.271 52(40)
¹⁴³Nd	0.121 74(26)
¹⁴⁴Nd	0.237 98(19)
¹⁴⁵Nd	0.082 93(12)
¹⁴⁶Nd	0.171 89(32)
¹⁴⁸Nd	0.057 56(21)
¹⁵⁰Nd	0.056 38(28)

Promethium Pm, Z = 61

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 145.

Samarium Sm, Z = 62

150.36(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.7 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2005, doi:10.1351/pac200678112051

8 values recommended since 1902

Year	Value	Report
2005	150.36(2)	doi:10.1351/pac200678112051
1979	150.36(3)	doi:10.1351/pac198052102349
1969	150.4(1)	doi:10.1351/pac197021010091
1955	150.35	doi:10.1021/ja01595a001
1925	150.43	doi:10.1039/CT9252700913
1909	150.4	doi:10.1021/ja01931a001
1905	150.3	doi:10.1021/ja01979a001
1902	150	doi:10.1007/BF01370337

7 isotopes with an abundance

¹⁴⁴Sm¹⁴⁷Sm¹⁴⁸Sm¹⁴⁹Sm¹⁵⁰Sm¹⁵²Sm¹⁵⁴Sm

Isotope	Amount fraction
¹⁴⁴Sm	0.0308(4)
¹⁴⁷Sm	0.1500(14)
¹⁴⁸Sm	0.1125(9)
¹⁴⁹Sm	0.1382(10)
¹⁵⁰Sm	0.0737(9)
¹⁵²Sm	0.2674(9)
¹⁵⁴Sm	0.2274(14)

Europium Eu, Z = 63

151.964(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.3 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1995, doi:10.1351/pac199668122339

6 values recommended since 1902

Year	Value	Report
1995	151.964(1)	doi:10.1351/pac199668122339
1985	151.965(9)	doi:10.1351/pac198658121677
1969	151.96(1)	doi:10.1351/pac197021010091
1961	151.96	doi:10.1021/ja00881a001
1909	152	doi:10.1021/ja01931a001
1902	152	doi:10.1007/BF01370337

2 isotopes with an abundance

¹⁵¹Eu¹⁵³Eu

Isotope	Amount fraction
¹⁵¹Eu	0.4781(6)
¹⁵³Eu	0.5219(6)

Gadolinium Gd, Z = 64

157.249(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.5 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2024

9 values recommended since 1902

Year	Value	Report
2024	157.249(2)
1969	157.25(3)	doi:10.1351/pac197021010091
1961	157.25	doi:10.1021/ja00881a001
1955	157.26	doi:10.1021/ja01595a001
1937	156.9	doi:10.1039/JR9370001900
1931	157.3	doi:10.1039/JR9310001617
1925	157.26	doi:10.1039/CT9252700913
1909	157.3	doi:10.1021/ja01931a001
1902	156	doi:10.1007/BF01370337

7 isotopes with an abundance

¹⁵²Gd¹⁵⁴Gd¹⁵⁵Gd¹⁵⁶Gd¹⁵⁷Gd¹⁵⁸Gd¹⁶⁰Gd

Isotope	Amount fraction
¹⁵²Gd	0.002 04(2)
¹⁵⁴Gd	0.021 87(9)
¹⁵⁵Gd	0.148 28(60)
¹⁵⁶Gd	0.204 93(22)
¹⁵⁷Gd	0.156 57(17)
¹⁵⁸Gd	0.248 20(20)
¹⁶⁰Gd	0.218 11(28)

Terbium Tb, Z = 65

158.925 354(7)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 8.8 × 10^-8.

issued 2021, doi:10.1515/pac-2019-0603

10 values recommended since 1902

Year	Value	Report
2021	158.925 354(7)	doi:10.1515/pac-2019-0603
2017	158.925 354(8)	doi:10.1515/pac-2019-0603
2005	158.925 35(2)	doi:10.1351/pac200678112051
1995	158.925 34(2)	doi:10.1351/pac199668122339
1985	158.925 34(3)	doi:10.1351/pac198658121677
1969	158.9254(1)	doi:10.1351/pac197021010091
1961	158.924	doi:10.1021/ja00881a001
1953	158.93	doi:10.1039/JR9540004713
1907	159.2	doi:10.1021/ja01956a001
1902	160	doi:10.1007/BF01370337

1 isotope with an abundance

¹⁵⁹Tb

Isotope	Amount fraction
¹⁵⁹Tb	1

Dysprosium Dy, Z = 66

162.500(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.2 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2001, doi:10.1351/pac200375081107

7 values recommended since 1908

Year	Value	Report
2001	162.500(1)	doi:10.1351/pac200375081107
1969	162.50(3)	doi:10.1351/pac197021010091
1961	162.50	doi:10.1021/ja00881a001
1955	162.51	doi:10.1021/ja01595a001
1931	162.46	doi:10.1039/JR9310001617
1925	162.52	doi:10.1039/CT9252700913
1908	162.5	doi:10.1021/ja01943a001

7 isotopes with an abundance

¹⁵⁶Dy¹⁵⁸Dy¹⁶⁰Dy¹⁶¹Dy¹⁶²Dy¹⁶³Dy¹⁶⁴Dy

Isotope	Amount fraction
¹⁵⁶Dy	0.000 56(3)
¹⁵⁸Dy	0.000 95(3)
¹⁶⁰Dy	0.023 29(18)
¹⁶¹Dy	0.188 89(42)
¹⁶²Dy	0.254 75(36)
¹⁶³Dy	0.248 96(42)
¹⁶⁴Dy	0.282 60(54)

Holmium Ho, Z = 67

164.930 329(5)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 6.1 × 10^-8.

issued 2021, doi:10.1515/pac-2019-0603

12 values recommended since 1913

Year	Value	Report
2021	164.930 329(5)	doi:10.1515/pac-2019-0603
2017	164.930 328(7)	doi:10.1515/pac-2019-0603
2013	164.930 33(2)	doi:10.1515/pac-2015-0305
1995	164.930 32(2)	doi:10.1351/pac199668122339
1985	164.930 32(3)	doi:10.1351/pac198658121677
1971	164.9304(1)	doi:10.1351/pac197230030637
1969	164.9303(1)	doi:10.1351/pac197021010091
1961	164.930	doi:10.1021/ja00881a001
1941	164.94	doi:10.1039/JR9410000146
1931	163.5	doi:10.1039/JR9310001617
1925	163.4	doi:10.1039/CT9252700913
1913	163.5	doi:10.1021/ja02212a001

1 isotope with an abundance

¹⁶⁵Ho

Isotope	Amount fraction
¹⁶⁵Ho	1

Erbium Er, Z = 68

167.259(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.6 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1999, doi:10.1351/pac200173040667

9 values recommended since 1902

Year	Value	Report
1999	167.259(3)	doi:10.1351/pac200173040667
1969	167.26(3)	doi:10.1351/pac197021010091
1961	167.26	doi:10.1021/ja00881a001
1955	167.27	doi:10.1021/ja01595a001
1938	167.2	doi:10.1039/JR9380001101
1931	167.64	doi:10.1039/JR9310001617
1912	167.7	doi:10.1021/ja02224a601
1909	167.4	doi:10.1021/ja01931a001
1902	166	doi:10.1007/BF01370337

6 isotopes with an abundance

¹⁶²Er¹⁶⁴Er¹⁶⁶Er¹⁶⁷Er¹⁶⁸Er¹⁷⁰Er

Isotope	Amount fraction
¹⁶²Er	0.001 39(5)
¹⁶⁴Er	0.016 01(3)
¹⁶⁶Er	0.335 03(36)
¹⁶⁷Er	0.228 69(9)
¹⁶⁸Er	0.269 78(18)
¹⁷⁰Er	0.149 10(36)

Thulium Tm, Z = 69

168.934 219(5)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 5.9 × 10^-8.

issued 2021, doi:10.1515/pac-2019-0603

12 values recommended since 1902

Year	Value	Report
2021	168.934 219(5)	doi:10.1515/pac-2019-0603
2017	168.934 218(6)	doi:10.1515/pac-2019-0603
2013	168.934 22(2)	doi:10.1515/pac-2015-0305
1995	168.934 21(2)	doi:10.1351/pac199668122339
1985	168.934 21(3)	doi:10.1351/pac198658121677
1969	168.9342(1)	doi:10.1351/pac197021010091
1961	168.934	doi:10.1021/ja00881a001
1953	168.94	doi:10.1039/JR9540004713
1925	169.4	doi:10.1039/CT9252700913
1922	169.9	doi:10.1021/ja01441a001
1909	168.5	doi:10.1021/ja01931a001
1902	171	doi:10.1007/BF01370337

1 isotope with an abundance

¹⁶⁹Tm

Isotope	Amount fraction
¹⁶⁹Tm	1

Ytterbium Yb, Z = 70

173.045(10)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.2 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2015, doi:10.1515/pac-2019-0603

9 values recommended since 1902

Year	Value	Report
2015	173.045(10)	doi:10.1515/pac-2019-0603
2007	173.054(5)	doi:10.1351/PAC-REP-09-08-03
1969	173.04(3)	doi:10.1351/pac197021010091
1934	173.04	doi:10.1039/JR9340000499
1931	173.5	doi:10.1039/JR9310001617
1925	173.6	doi:10.1039/CT9252700913
1916	173.5	doi:10.1021/ja02176a001
1909	172	doi:10.1021/ja01931a001
1902	173	doi:10.1007/BF01370337

7 isotopes with an abundance

¹⁶⁸Yb¹⁷⁰Yb¹⁷¹Yb¹⁷²Yb¹⁷³Yb¹⁷⁴Yb¹⁷⁶Yb

Isotope	Amount fraction
¹⁶⁸Yb	0.001 26(1)
¹⁷⁰Yb	0.030 23(2)
¹⁷¹Yb	0.142 16(7)
¹⁷²Yb	0.217 54(10)
¹⁷³Yb	0.160 98(9)
¹⁷⁴Yb	0.318 96(26)
¹⁷⁶Yb	0.128 87(30)

Lutetium Lu, Z = 71

174.966 69(5)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 5.7 × 10^-7.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2024

9 values recommended since 1909

Year	Value	Report
2024	174.966 69(5)
2007	174.9668(1)	doi:10.1351/PAC-REP-09-08-03
1981	174.967(1)	doi:10.1351/pac198355071101
1977	174.967(3)	doi:10.1351/pac197951020405
1969	174.97(1)	doi:10.1351/pac197021010091
1961	174.97	doi:10.1021/ja00881a001
1940	174.99	doi:10.1039/JR9400000475
1916	175	doi:10.1021/ja02176a001
1909	174	doi:10.1021/ja01931a001

2 isotopes with an abundance

¹⁷⁵Lu¹⁷⁶Lu

Isotope	Amount fraction
¹⁷⁵Lu	0.974 14(5)
¹⁷⁶Lu	0.025 86(5)

Hafnium Hf, Z = 72

178.486(6)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 6.7 × 10^-5.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2019, doi:10.1515/pac-2019-0603

6 values recommended since 1931

Year	Value	Report
2019	178.486(6)	doi:10.1515/pac-2019-0603
1985	178.49(2)	doi:10.1351/pac198658121677
1969	178.49(3)	doi:10.1351/pac197021010091
1961	178.49	doi:10.1021/ja00881a001
1955	178.50	doi:10.1021/ja01595a001
1931	178.6	doi:10.1039/JR9310001617

6 isotopes with an abundance

¹⁷⁴Hf¹⁷⁶Hf¹⁷⁷Hf¹⁷⁸Hf¹⁷⁹Hf¹⁸⁰Hf

Isotope	Amount fraction
¹⁷⁴Hf	0.001 61(2)
¹⁷⁶Hf	0.0524(14)
¹⁷⁷Hf	0.1858(9)
¹⁷⁸Hf	0.2728(6)
¹⁷⁹Hf	0.1363(3)
¹⁸⁰Hf	0.3512(16)

Tantalum Ta, Z = 73

180.947 88(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.2 × 10^-7.

issued 2005, doi:10.1351/pac200678112051

11 values recommended since 1902

Year	Value	Report
2005	180.947 88(2)	doi:10.1351/pac200678112051
1979	180.9479(1)	doi:10.1351/pac198052102349
1969	180.9479(3)	doi:10.1351/pac197021010091
1961	180.948	doi:10.1021/ja00881a001
1953	180.95	doi:10.1039/JR9540004713
1936	180.88	doi:10.1039/JR9370001893
1931	181.4	doi:10.1039/JR9310001617
1912	181.5	doi:10.1021/ja02224a601
1909	181	doi:10.1021/ja01931a001
1907	181	doi:10.1021/ja01956a001
1902	183	doi:10.1007/BF01370337

2 isotopes with an abundance

¹⁸⁰Ta¹⁸¹Ta

Isotope	Amount fraction
¹⁸⁰Ta	0.000 1176(23)
¹⁸¹Ta	0.999 8824(23)

Tungsten W, Z = 74

183.84(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.1 × 10^-4.

issued 1991, doi:10.1351/pac199264101519

6 values recommended since 1902

Year	Value	Report
1991	183.84(1)	doi:10.1351/pac199264101519
1969	183.85(3)	doi:10.1351/pac197021010091
1961	183.85	doi:10.1021/ja00881a001
1955	183.86	doi:10.1021/ja01595a001
1938	183.92	doi:10.1039/JR9380001101
1902	184	doi:10.1007/BF01370337

5 isotopes with an abundance

¹⁸⁰W¹⁸²W¹⁸³W¹⁸⁴W¹⁸⁶W

Isotope	Amount fraction
¹⁸⁰W	0.0012(1)
¹⁸²W	0.2650(16)
¹⁸³W	0.1431(4)
¹⁸⁴W	0.3064(2)
¹⁸⁶W	0.2843(19)

Rhenium Re, Z = 75

186.207(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 1.1 × 10^-5.

issued 1973, doi:10.1351/pac197437040589

5 values recommended since 1931

Year	Value	Report
1973	186.207(1)	doi:10.1351/pac197437040589
1969	186.2(1)	doi:10.1351/pac197021010091
1961	186.2	doi:10.1021/ja00881a001
1955	186.22	doi:10.1021/ja01595a001
1931	186.31	doi:10.1039/JR9310001617

2 isotopes with an abundance

¹⁸⁵Re¹⁸⁷Re

Isotope	Amount fraction
¹⁸⁵Re	0.3740(5)
¹⁸⁷Re	0.6260(5)

Osmium Os, Z = 76

190.23(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.2 × 10^-4.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 1991, doi:10.1351/pac199264101519

7 values recommended since 1902

Year	Value	Report
1991	190.23(3)	doi:10.1351/pac199264101519
1969	190.2(1)	doi:10.1351/pac197021010091
1938	190.2	doi:10.1039/JR9380001101
1934	191.5	doi:10.1039/JR9340000499
1925	190.8	doi:10.1039/CT9252700913
1909	190.9	doi:10.1021/ja01931a001
1902	191	doi:10.1007/BF01370337

7 isotopes with an abundance

¹⁸⁴Os¹⁸⁶Os¹⁸⁷Os¹⁸⁸Os¹⁸⁹Os¹⁹⁰Os¹⁹²Os

Isotope	Amount fraction
¹⁸⁴Os	0.0002(2)
¹⁸⁶Os	0.0159(64)
¹⁸⁷Os	0.0196(17)
¹⁸⁸Os	0.1324(27)
¹⁸⁹Os	0.1615(23)
¹⁹⁰Os	0.2626(20)
¹⁹²Os	0.4078(32)

Iridium Ir, Z = 77

192.217(2)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.1 × 10^-5.

issued 2017, doi:10.1515/pac-2019-0603

6 values recommended since 1902

Year	Value	Report
2017	192.217(2)	doi:10.1515/pac-2019-0603
1993	192.217(3)	doi:10.1351/pac199466122423
1969	192.22(3)	doi:10.1351/pac197021010091
1953	192.2	doi:10.1039/JR9540004713
1909	193.1	doi:10.1021/ja01931a001
1902	193	doi:10.1007/BF01370337

2 isotopes with an abundance

¹⁹¹Ir¹⁹³Ir

Isotope	Amount fraction
¹⁹¹Ir	0.3723(9)
¹⁹³Ir	0.6277(9)

Platinum Pt, Z = 78

195.084(9)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 9.2 × 10^-5.

issued 2005, doi:10.1351/pac200678112051

9 values recommended since 1902

Year	Value	Report
2005	195.084(9)	doi:10.1351/pac200678112051
1995	195.078(2)	doi:10.1351/pac199668122339
1979	195.08(3)	doi:10.1351/pac198052102349
1969	195.09(3)	doi:10.1351/pac197021010091
1955	195.09	doi:10.1021/ja01595a001
1925	195.23	doi:10.1039/CT9252700913
1911	195.2	doi:10.1021/ja01928a001
1909	195	doi:10.1021/ja01931a001
1902	194.8	doi:10.1007/BF01370337

6 isotopes with an abundance

¹⁹⁰Pt¹⁹²Pt¹⁹⁴Pt¹⁹⁵Pt¹⁹⁶Pt¹⁹⁸Pt

Isotope	Amount fraction
¹⁹⁰Pt	0.000 12(2)
¹⁹²Pt	0.007 82(24)
¹⁹⁴Pt	0.328 64(410)
¹⁹⁵Pt	0.337 75(240)
¹⁹⁶Pt	0.252 11(340)
¹⁹⁸Pt	0.073 56(130)

Gold Au, Z = 79

196.966 570(4)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 4.1 × 10^-8.

issued 2017, doi:10.1515/pac-2019-0603

9 values recommended since 1902

Year	Value	Report
2017	196.966 570(4)	doi:10.1515/pac-2019-0603
2013	196.966 569(5)	doi:10.1515/pac-2015-0305
2005	196.966 569(4)	doi:10.1351/pac200678112051
1995	196.966 55(2)	doi:10.1351/pac199668122339
1985	196.966 54(3)	doi:10.1351/pac198658121677
1969	196.9665(1)	doi:10.1351/pac197021010091
1961	196.967	doi:10.1021/ja00881a001
1953	197	doi:10.1039/JR9540004713
1902	197.2	doi:10.1007/BF01370337

1 isotope with an abundance

¹⁹⁷Au

Isotope	Amount fraction
¹⁹⁷Au	1

Mercury Hg, Z = 80

200.592(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.0 × 10^-5.

issued 2011, doi:10.1351/PAC-REP-13-03-02

8 values recommended since 1902

Year	Value	Report
2011	200.592(3)	doi:10.1351/PAC-REP-13-03-02
1989	200.59(2)	doi:10.1351/pac199163070975
1969	200.59(3)	doi:10.1351/pac197021010091
1961	200.59	doi:10.1021/ja00881a001
1925	200.61	doi:10.1039/CT9252700913
1912	200.6	doi:10.1021/ja02224a601
1903	200	doi:10.1021/ja02003a001
1902	200.3	doi:10.1007/BF01370337

7 isotopes with an abundance

¹⁹⁶Hg¹⁹⁸Hg¹⁹⁹Hg²⁰⁰Hg²⁰¹Hg²⁰²Hg²⁰⁴Hg

Isotope	Amount fraction
¹⁹⁶Hg	0.0015(1)
¹⁹⁸Hg	0.1004(3)
¹⁹⁹Hg	0.1694(12)
²⁰⁰Hg	0.2314(9)
²⁰¹Hg	0.1317(9)
²⁰²Hg	0.2974(13)
²⁰⁴Hg	0.0682(4)

Thallium Tl, Z = 81

[204.382, 204.385]

Standard atomic weight, given as an interval. Relative uncertainty 1.5 × 10^-5.

issued 2009, doi:10.1351/PAC-REP-10-09-14

8 values recommended since 1902

Year	Value	Report
2009	[204.382, 204.385]	doi:10.1351/PAC-REP-10-09-14
1985	204.3833(2)	doi:10.1351/pac198658121677
1979	204.383(1)	doi:10.1351/pac198052102349
1969	204.37(3)	doi:10.1351/pac197021010091
1961	204.37	doi:10.1021/ja00881a001
1925	204.39	doi:10.1039/CT9252700913
1909	204	doi:10.1021/ja01931a001
1902	204.1	doi:10.1007/BF01370337

2 isotopes with an abundance

²⁰³Tl²⁰⁵Tl

Isotope	Amount fraction
²⁰³Tl	[0.2944, 0.2959]
²⁰⁵Tl	[0.7041, 0.7056]

Lead Pb, Z = 82

[206.14, 207.94]

Standard atomic weight, given as an interval. Relative uncertainty 8.7 × 10^-3.

issued 2020, doi:10.1515/pac-2019-0603

8 values recommended since 1902

Year	Value	Report
2020	[206.14, 207.94]	doi:10.1515/pac-2019-0603
1969	207.2(1)	doi:10.1351/pac197021010091
1961	207.19	doi:10.1021/ja00881a001
1937	207.21	doi:10.1039/JR9370001900
1931	207.22	doi:10.1039/JR9310001617
1916	207.20	doi:10.1021/ja02176a001
1909	207.10	doi:10.1021/ja01931a001
1902	206.9	doi:10.1007/BF01370337

4 isotopes with an abundance

²⁰⁴Pb²⁰⁶Pb²⁰⁷Pb²⁰⁸Pb

Isotope	Amount fraction
²⁰⁴Pb	[0.0000, 0.0158]
²⁰⁶Pb	[0.0190, 0.8673]
²⁰⁷Pb	[0.0035, 0.2351]
²⁰⁸Pb	[0.0338, 0.9775]

Bismuth Bi, Z = 83

208.980 40(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 9.6 × 10^-8.

issued 2005, doi:10.1351/pac200678112051

10 values recommended since 1902

Year	Value	Report
2005	208.980 40(1)	doi:10.1351/pac200678112051
1995	208.980 38(2)	doi:10.1351/pac199668122339
1985	208.980 37(3)	doi:10.1351/pac198658121677
1971	208.9804(1)	doi:10.1351/pac197230030637
1969	208.9806(1)	doi:10.1351/pac197021010091
1961	208.980	doi:10.1021/ja00881a001
1925	209	doi:10.1039/CT9252700913
1922	209	doi:10.1021/ja01441a001
1907	208	doi:10.1021/ja01956a001
1902	208.5	doi:10.1007/BF01370337

1 isotope with an abundance

²⁰⁹Bi

Isotope	Amount fraction
²⁰⁹Bi	1

Polonium Po, Z = 84

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 209.

Astatine At, Z = 85

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 210.

Radon Rn, Z = 86

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 222.

Francium Fr, Z = 87

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 223.

Radium Ra, Z = 88

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 226.

Actinium Ac, Z = 89

No standard atomic weight: the element has no stable isotope. The longest-lived isotope has mass number 227.

Thorium Th, Z = 90

232.0377(4)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 3.4 × 10^-6.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

issued 2013, doi:10.1515/pac-2015-0305

10 values recommended since 1902

Year	Value	Report
2013	232.0377(4)	doi:10.1515/pac-2015-0305
2005	232.038 06(2)	doi:10.1351/pac200678112051
1969	232.0381(1)	doi:10.1351/pac197021010091
1961	232.038	doi:10.1021/ja00881a001
1953	232.05	doi:10.1039/JR9540004713
1931	232.12	doi:10.1039/JR9310001617
1920	232.15	doi:10.1021/ja02233a600
1911	232.4	doi:10.1021/ja01928a001
1909	232.42	doi:10.1021/ja01931a001
1902	232.5	doi:10.1007/BF01370337

2 isotopes with an abundance

²³⁰Th²³²Th

Isotope	Amount fraction
²³⁰Th	0.0002(2)
²³²Th	0.9998(2)

Protactinium Pa, Z = 91

231.035 88(1)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 8.7 × 10^-8.

issued 2017, doi:10.1515/pac-2019-0603

5 values recommended since 1936

Year	Value	Report
2017	231.035 88(1)	doi:10.1515/pac-2019-0603
1989	231.035 88(2)	doi:10.1351/pac199163070975
1985	231.035 88(2)	doi:10.1351/pac198658121677
1969	231.0359(1)	doi:10.1351/pac197021010091
1936	231	doi:10.1039/JR9370001893

1 isotope with an abundance

²³¹Pa

Isotope	Amount fraction
²³¹Pa	1

Uranium U, Z = 92

238.028 91(3)

Standard atomic weight, given as a value with its standard uncertainty in brackets. Relative uncertainty 2.5 × 10^-7.

g Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.
m Modified isotopic compositions may be found in commercially available material because the material has been subjected to some undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.

issued 1999, doi:10.1351/pac200173040667

10 values recommended since 1902

Year	Value	Report
1999	238.028 91(3)	doi:10.1351/pac200173040667
1979	238.0289(1)	doi:10.1351/pac198052102349
1969	238.029(1)	doi:10.1351/pac197021010091
1961	238.03	doi:10.1021/ja00881a001
1937	238.07	doi:10.1039/JR9370001900
1931	238.14	doi:10.1039/JR9310001617
1925	238.17	doi:10.1039/CT9252700913
1916	238.2	doi:10.1021/ja02176a001
1903	238.5	doi:10.1021/ja02003a001
1902	239.5	doi:10.1007/BF01370337

3 isotopes with an abundance

²³⁴U²³⁵U²³⁸U

Isotope	Amount fraction
²³⁴U	0.000 054(5)
²³⁵U	0.007 204(6)
²³⁸U	0.992 742(10)

Neptunium Np, Z = 93

No standard atomic weight.

Plutonium Pu, Z = 94

No standard atomic weight.

Americium Am, Z = 95

No standard atomic weight.

Curium Cm, Z = 96

No standard atomic weight.

Berkelium Bk, Z = 97

No standard atomic weight.

Californium Cf, Z = 98

No standard atomic weight.

Einsteinium Es, Z = 99

No standard atomic weight.

Fermium Fm, Z = 100

No standard atomic weight.

Mendelevium Md, Z = 101

No standard atomic weight.

Nobelium No, Z = 102

No standard atomic weight.

Lawrencium Lr, Z = 103

No standard atomic weight.

Rutherfordium Rf, Z = 104

No standard atomic weight.

Dubnium Db, Z = 105

No standard atomic weight.

Seaborgium Sg, Z = 106

No standard atomic weight.

Bohrium Bh, Z = 107

No standard atomic weight.

Hassium Hs, Z = 108

No standard atomic weight.

Meitnerium Mt, Z = 109

No standard atomic weight.

Darmstadtium Ds, Z = 110

No standard atomic weight.

Roentgenium Rg, Z = 111

No standard atomic weight.

Copernicium Cn, Z = 112

No standard atomic weight.

Nihonium Nh, Z = 113

No standard atomic weight.

Flerovium Fl, Z = 114

No standard atomic weight.

Moscovium Mc, Z = 115

No standard atomic weight.

Livermorium Lv, Z = 116

No standard atomic weight.

Tennessine Ts, Z = 117

No standard atomic weight.

Oganesson Og, Z = 118

No standard atomic weight.

Changes since 1902

Standard atomic weights changed per year

Isotopic composition

Amount fraction of each isotope, in order of mass number

lightest isotope
heaviest isotope

H 1¹H²H

He 2³He⁴He

Li 3⁶Li⁷Li

Be 4⁹Be

B 5¹⁰B¹¹B

C 6¹²C¹³C

N 7¹⁴N¹⁵N

O 8¹⁶O¹⁷O¹⁸O

F 9¹⁹F

Ne 10²⁰Ne²¹Ne²²Ne

Na 11²³Na

Mg 12²⁴Mg²⁵Mg²⁶Mg

Al 13²⁷Al

Si 14²⁸Si²⁹Si³⁰Si

P 15³¹P

S 16³²S³³S³⁴S³⁶S

Cl 17³⁵Cl³⁷Cl

Ar 18³⁶Ar³⁸Ar⁴⁰Ar

K 19³⁹K⁴⁰K⁴¹K

Ca 20⁴⁰Ca⁴²Ca⁴³Ca⁴⁴Ca⁴⁶Ca⁴⁸Ca

Sc 21⁴⁵Sc

Ti 22⁴⁶Ti⁴⁷Ti⁴⁸Ti⁴⁹Ti⁵⁰Ti

V 23⁵⁰V⁵¹V

Cr 24⁵⁰Cr⁵²Cr⁵³Cr⁵⁴Cr

Mn 25⁵⁵Mn

Fe 26⁵⁴Fe⁵⁶Fe⁵⁷Fe⁵⁸Fe

Co 27⁵⁹Co

Ni 28⁵⁸Ni⁶⁰Ni⁶¹Ni⁶²Ni⁶⁴Ni

Cu 29⁶³Cu⁶⁵Cu

Zn 30⁶⁴Zn⁶⁶Zn⁶⁷Zn⁶⁸Zn⁷⁰Zn

Ga 31⁶⁹Ga⁷¹Ga

Ge 32⁷⁰Ge⁷²Ge⁷³Ge⁷⁴Ge⁷⁶Ge

As 33⁷⁵As

Se 34⁷⁴Se⁷⁶Se⁷⁷Se⁷⁸Se⁸⁰Se⁸²Se

Br 35⁷⁹Br⁸¹Br

Kr 36⁷⁸Kr⁸⁰Kr⁸²Kr⁸³Kr⁸⁴Kr⁸⁶Kr

Rb 37⁸⁵Rb⁸⁷Rb

Sr 38⁸⁴Sr⁸⁶Sr⁸⁷Sr⁸⁸Sr

Y 39⁸⁹Y

Zr 40⁹⁰Zr⁹¹Zr⁹²Zr⁹⁴Zr⁹⁶Zr

Nb 41⁹³Nb

Mo 42⁹²Mo⁹⁴Mo⁹⁵Mo⁹⁶Mo⁹⁷Mo⁹⁸Mo¹⁰⁰Mo

Ru 44⁹⁶Ru⁹⁸Ru⁹⁹Ru¹⁰⁰Ru¹⁰¹Ru¹⁰²Ru¹⁰⁴Ru

Rh 45¹⁰³Rh

Pd 46¹⁰²Pd¹⁰⁴Pd¹⁰⁵Pd¹⁰⁶Pd¹⁰⁸Pd¹¹⁰Pd

Ag 47¹⁰⁷Ag¹⁰⁹Ag

Cd 48¹⁰⁶Cd¹⁰⁸Cd¹¹⁰Cd¹¹¹Cd¹¹²Cd¹¹³Cd¹¹⁴Cd¹¹⁶Cd

In 49¹¹³In¹¹⁵In

Sn 50¹¹²Sn¹¹⁴Sn¹¹⁵Sn¹¹⁶Sn¹¹⁷Sn¹¹⁸Sn¹¹⁹Sn¹²⁰Sn¹²²Sn¹²⁴Sn

Sb 51¹²¹Sb¹²³Sb

Te 52¹²⁰Te¹²²Te¹²³Te¹²⁴Te¹²⁵Te¹²⁶Te¹²⁸Te¹³⁰Te

I 53¹²⁷I

Xe 54¹²⁴Xe¹²⁶Xe¹²⁸Xe¹²⁹Xe¹³⁰Xe¹³¹Xe¹³²Xe¹³⁴Xe¹³⁶Xe

Cs 55¹³³Cs

Ba 56¹³⁰Ba¹³²Ba¹³⁴Ba¹³⁵Ba¹³⁶Ba¹³⁷Ba¹³⁸Ba

La 57¹³⁸La¹³⁹La

Ce 58¹³⁶Ce¹³⁸Ce¹⁴⁰Ce¹⁴²Ce

Pr 59¹⁴¹Pr

Nd 60¹⁴²Nd¹⁴³Nd¹⁴⁴Nd¹⁴⁵Nd¹⁴⁶Nd¹⁴⁸Nd¹⁵⁰Nd

Sm 62¹⁴⁴Sm¹⁴⁷Sm¹⁴⁸Sm¹⁴⁹Sm¹⁵⁰Sm¹⁵²Sm¹⁵⁴Sm

Eu 63¹⁵¹Eu¹⁵³Eu

Gd 64¹⁵²Gd¹⁵⁴Gd¹⁵⁵Gd¹⁵⁶Gd¹⁵⁷Gd¹⁵⁸Gd¹⁶⁰Gd

Tb 65¹⁵⁹Tb

Dy 66¹⁵⁶Dy¹⁵⁸Dy¹⁶⁰Dy¹⁶¹Dy¹⁶²Dy¹⁶³Dy¹⁶⁴Dy

Ho 67¹⁶⁵Ho

Er 68¹⁶²Er¹⁶⁴Er¹⁶⁶Er¹⁶⁷Er¹⁶⁸Er¹⁷⁰Er

Tm 69¹⁶⁹Tm

Yb 70¹⁶⁸Yb¹⁷⁰Yb¹⁷¹Yb¹⁷²Yb¹⁷³Yb¹⁷⁴Yb¹⁷⁶Yb

Lu 71¹⁷⁵Lu¹⁷⁶Lu

Hf 72¹⁷⁴Hf¹⁷⁶Hf¹⁷⁷Hf¹⁷⁸Hf¹⁷⁹Hf¹⁸⁰Hf

Ta 73¹⁸⁰Ta¹⁸¹Ta

W 74¹⁸⁰W¹⁸²W¹⁸³W¹⁸⁴W¹⁸⁶W

Re 75¹⁸⁵Re¹⁸⁷Re

Os 76¹⁸⁴Os¹⁸⁶Os¹⁸⁷Os¹⁸⁸Os¹⁸⁹Os¹⁹⁰Os¹⁹²Os

Ir 77¹⁹¹Ir¹⁹³Ir

Pt 78¹⁹⁰Pt¹⁹²Pt¹⁹⁴Pt¹⁹⁵Pt¹⁹⁶Pt¹⁹⁸Pt

Au 79¹⁹⁷Au

Hg 80¹⁹⁶Hg¹⁹⁸Hg¹⁹⁹Hg²⁰⁰Hg²⁰¹Hg²⁰²Hg²⁰⁴Hg

Tl 81²⁰³Tl²⁰⁵Tl

Pb 82²⁰⁴Pb²⁰⁶Pb²⁰⁷Pb²⁰⁸Pb

Bi 83²⁰⁹Bi

Th 90²³⁰Th²³²Th

Pa 91²³¹Pa

U 92²³⁴U²³⁵U²³⁸U

Current values from the table of standard atomic weights and the isotopic abundances. Historical values: Historical changes of standard atomic weights, CIAAW, ciaaw.org, © CIAAW 2016–2024, reproduced with the acknowledgement its terms ask for.