37Rb Rubidium Ar (Rb) = 85.4678(3) g [Since 1969] Isotope Atomic mass/u 

85Rb 84.911 7924(27) 0.7217(2) 
87Rb 86.909 1858(28) 0.2783(2) 

38Sr Strontium Ar (Sr) = 87.62(1) g, r [Since 1969] Isotope Atomic mass/u 

84Sr 83.913 426(4) 0.0056(1) 
86Sr 85.909 2647(25) 0.0986(1) 
87Sr 86.908 8816(25) 0.0700(1) 
88Sr 87.905 6167(25) 0.8258(1) 

39Y Yttrium Ar (Y) = 88.905 85(2) [Since 1985] Isotope Atomic mass/u 

89Y 88.905 8485(26) 1.0000 

40Zr Zirconium Ar (Zr) = 91.224(2) g [Since 1983] Isotope Atomic mass/u 

90Zr 89.904 7022(24) 0.5145(40) 
91Zr 90.905 6434(23) 0.1122(5) 
92Zr 91.905 0386(23) 0.1715(8) 
94Zr 93.906 3144(26) 0.1738(28) 
96Zr 95.908 275(3) 0.0280(9) 

41Nb Niobium Ar (Nb) = 92.906 38(2) [Since 1985] Isotope Atomic mass/u 

93Nb 92.906 3762(24) 1.0000 

42Mo Molybdenum Ar (Mo) = 95.94 (2) g [Since 2001] Isotope Atomic mass/u 

92Mo 91.906 810(4) 0.1477(31) 
94Mo 93.905 0867(20) 0.0923(10) 
95Mo 94.905 8406(20) 0.1590(9) 
96Mo 95.904 6780(20) 0.1668(1) 
97Mo 96.906 0201(20) 0.0956(5) 
98Mo 97.905 4069(20) 0.2419(26) 
100Mo 99.907 476(6) 0.0967(20) 


43Tc Technetium 

44Ru Ruthenium Ar (Ru) = 101.07(2) g [Since 1983] Isotope Atomic mass/u 

96Ru 95.907 604(9) 0.0554(14) 
98Ru 97.905 287(7) 0.0187(3) 
99Ru 98.905 9385(22) 0.1276(14) 
100Ru 99.904 2189(22) 0.1260(7) 
101Ru 100.905 5815(22) 0.1706(2) 
102Ru 101.904 3488(22) 0.3155(14) 
104Ru 103.905 430(4) 0.1862(27) 

45Rh Rhodium Ar (Rh) = 102.905 50(2) [Since 1995] Isotope Atomic mass/u 

103Rh 102.905 504(3) 1.0000 

46Pd Palladium Ar (Pd) = 106.42(1) g [Since 1979] Isotope Atomic mass/u 

102Pd 101.905 607(3) 0.0102(1) 
104Pd 103.904 034(5) 0.1114(8) 
105Pd 104.905 083(5) 0.2233(8) 
106Pd 105.903 484(5) 0.2733(3) 
108Pd 107.903 895(4) 0.2646(9) 
110Pd 109.905 153(12) 0.1172(9) 

47Ag Silver (Argentum) Ar (Ag) = 107.8682(2) g [Since 1985] Isotope Atomic mass/u 

107Ag 106.905 093(6) 0.518 39(8) 
109Ag 108.904 756(3) 0.481 61(8) 

48Cd Cadmium Ar (Cd) = 112.411(8) g [Since 1985] Isotope Atomic mass/u 

106Cd 105.906 458(6) 0.0125(6) 
108Cd 107.904 183(6) 0.0089(3) 
110Cd 109.903 006(3) 0.1249(18) 
111Cd 110.904 182(3) 0.1280(12) 
112Cd 111.902 7577(30) 0.2413(21) 
113Cd 112.904 4014(30) 0.1222(12) 
114Cd 113.903 3586(30) 0.2873(42) 
116Cd 115.904 756(3) 0.0749(18) 
49In Indium Ar (In) = 114.818(3) [Since 1991] Isotope Atomic mass/u 

113In 112.904 062(4) 0.0429(5) 
115In 114.903 879(40) 0.9571(5) 

50Sn Tin (Stannum) Ar (Sn) = 118.710(7) g [Since 1983] Isotope Atomic mass/u 

112Sn 111.904 822(5) 0.0097(1) 
114Sn 113.902 783(3) 0.0066(1) 
115Sn 114.903 347(3) 0.0034(1) 
116Sn 115.901 745(3) 0.1454(9) 
117Sn 116.902 955(3) 0.0768(7) 
118Sn 117.901 608(3) 0.2422(9) 
119Sn 118.903 311(3) 0.0859(4) 
120Sn 119.902 1985(27) 0.3258(9) 
122Sn 121.903 4411(29) 0.0463(3) 
124Sn 123.905 2745(15) 0.0579(5) 

51Sb Antimony (Stibium) Ar (Sb) = 121.760(1) g [Since 1993] Isotope Atomic mass/u 

121Sb 120.903 8222(26) 0.5721(5) 
123Sb 122.904 2160(22) 0.4279(5) 

52Te Tellurium Ar (Te) = 127.60(3) g [Since 1969] Isotope Atomic mass/u 

120Te 119.904 026(11) 0.0009(1) 
122Te 121.903 0558(29) 0.0255(12) 
123Te 122.904 2711(20) 0.0089(3) 
124Te 123.902 8188(16) 0.0474(14) 
125Te 124.904 4241(20) 0.0707(15) 
126Te 125.903 3049(20) 0.1884(25) 
128Te 127.904 4615(19) 0.3174(8) 
130Te 129.906 2229(21) 0.3408(62) 

53I Iodine Ar (I) = 126.904 47(3) [Since 1985] Isotope Atomic mass/u 

127I 126.904 468(4) 1.0000 

54Xe Xenon Ar (Xe) = 131.293(6) g, m [Since 1999] Isotope Atomic mass/u 

124Xe 123.905 8954(21) 0.000 952(3) 
126Xe 125.904 268(7) 0.000 890(2) 
128Xe 127.903 5305(15) 0.019 102(8) 
129Xe 128.904 7799(9) 0.264 006(82) 
130Xe 129.903 5089(11) 0.040 710(13) 
131Xe 130.905 0828(18) 0.212 324(30) 
132Xe 131.904 1546(15) 0.269 086(33) 
134Xe 133.905 3945(9) 0.104 357(21) 
136Xe 135.907 220(8) 0.088 573(44) 

55Cs Caesium (Cesium) Ar (Cs) = 132.905 45(2) [Since 1995] Isotope Atomic mass/u 

133Cs 132.905 447(3) 1.0000 

56Ba Barium Ar (Ba) = 137.327(7) [Since 1985] Isotope Atomic mass/u 

130Ba 129.906 311(7) 0.001 06(1) 
132Ba 131.905 056(3) 0.001 01(1) 
134Ba 133.904 504(3) 0.024 17(18) 
135Ba 134.905 684(3) 0.065 92(12) 
136Ba 135.904 571(3) 0.078 54(24) 
137Ba 136.905 822(3) 0.112 32(24) 
138Ba 137.905 242(3) 0.716 98(42) 

57La Lanthanum Ar (La) = 138.9055(2) g [Since 1985] Isotope Atomic mass/u 

138La 137.907 108(4) 0.000 90(1) 
139La 138.906 349(4) 0.999 10(1) 
58Ce Cerium Ar (Ce) = 140.116(1) g [Since 1995] Isotope Atomic mass/u 

136Ce 135.907 140(50) 0.001 85(2) 
138Ce 137.905 986(11) 0.002 51(2) 
140Ce 139.905 435(3) 0.884 50(51) 
142Ce 141.909 241(4) 0.111 14(51) 

59Pr Praseodymium Ar (Pr) = 140.907 65(2) [Since 1995] Isotope Atomic mass/u 

141Pr 140.907 648(3) 1.0000 

60Nd Neodymium Ar (Nd) = 144.24(3) g [Since 1969] Isotope Atomic mass/u 

142Nd 141.907 719(3) 0.272(5) 
143Nd 142.909 810(3) 0.122(2) 
144Nd 143.910 083(3) 0.238(3) 
145Nd 144.912 569(3) 0.083(1) 
146Nd 145.913 113(3) 0.172(3) 
148Nd 147.916 889(4) 0.057(1) 
150Nd 149.920 887(4) 0.056(2) 

62Sm Samarium Ar (Sm) = 150.36(3) g [Since 1979] Isotope Atomic mass/u 

144Sm 143.911 996(4) 0.0307(7) 
147Sm 146.914 894(3) 0.1499(18) 
148Sm 147.914 818(3) 0.1124(10) 
149Sm 148.917 180(3) 0.1382(7) 
150Sm 149.917 272(3) 0.0738(1) 
152Sm 151.919 729(3) 0.2675(16) 
154Sm 153.922 206(3) 0.2275(29) 

63Eu Europium Ar (Eu) = 151.964(1) g [Since 1995] Isotope Atomic mass/u 

151Eu 150.919 846(3) 0.4781(6) 
153Eu 152.921 227(3) 0.5219(6) 

64Gd Gadolinium Ar (Gd) = 157.25(3) g [Since 1969] Isotope Atomic mass/u 

152Gd 151.919 789(3) 0.0020(1) 
154Gd 153.920 862(3) 0.0218(3) 
155Gd 154.922 619(3) 0.1480(12) 
156Gd 155.922 120(3) 0.2047(9) 
157Gd 156.923 957(3) 0.1565(2) 
158Gd 157.924 101(3) 0.2484(7) 
160Gd 159.927 051(3) 0.2186(19) 

65Tb Terbium Ar (Tb) = 158.925 34(2) [Since 1995] Isotope Atomic mass/u Molar fraction 159Tb 158.925 343(3) 1.0000 
66Dy Dysprosium Ar (Dy) = 162.500(1) g [Since 2001] Isotope Atomic mass/u 

156Dy 155.924 278(7) 0.000 56(3) 
158Dy 157.924 405(4) 0.000 95(3) 
160Dy 159.925 194(3) 0.023 29(18) 
161Dy 160.926 930(3) 0.188 89(42) 
162Dy 161.926 795(3) 0.254 75(36) 
163Dy 162.928 728(3) 0.248 96(42) 
164Dy 163.929 171(3) 0.282 60(54) 

67Ho Holmium Ar (Ho) = 164.930 32(2) [Since 1995] Isotope Atomic mass/u 

165Ho 164.930 319(3) 1.0000 

68Er Erbium Ar (Er) = 167.259(3) g [Since 1999] Isotope Atomic mass/u 

162Er 161.928 775(4) 0.001 39(5) 
164Er 163.929 197(4) 0.016 01(3) 
166Er 165.930 290(3) 0.335 03(36) 
167Er 166.932 046(3) 0.228 69(9) 
168Er 167.932 368(3) 0.269 78(18) 
170Er 169.935 461(3) 0.149 10(36) 

69Tm Thulium Ar (Tm) = 168.934 21(2) [Since 1995] Isotope Atomic mass/u 

169Tm 168.934 211(3) 1.0000 
70Yb Ytterbium Ar (Yb) = 173.04(3) g [Since 1969] Isotope Atomic mass/u 

168Yb 167.933 895(5) 0.0013(1) 
170Yb 169.934 759(3) 0.0304(15) 
171Yb 170.936 323(3) 0.1428(57) 
172Yb 171.936 378(3) 0.2183(67) 
173Yb 172.938 207(3) 0.1613(27) 
174Yb 173.938 858(3) 0.3183(92) 
176Yb 175.942 569(3) 0.1276(41) 

71Lu Lutetium Ar (Lu) = 174.967(1) g [Since 1981] Isotope Atomic mass/u 

175Lu 174.940 7682(28) 0.9741(2) 
176Lu 175.942 6827(28) 0.0259(2) 

72Hf Hafnium Ar(Hf) = 178.49(2) [Since 1985] Isotope Atomic mass/u 

174Hf 173.940 042(4) 0.0016(1) 
176Hf 175.941 403(3) 0.0526(7) 
177Hf 176.943 2204(27) 0.1860(9) 
178Hf 177.943 6981(27) 0.2728(7) 
179Hf 178.945 8154(27) 0.1362(2) 
180Hf 179.946 5488(27) 0.3508(16) 
73Ta Tantalum Ar (Ta) = 180.9479(1) [Since 1979] Isotope Atomic Mass/u 

180Ta 179.947 466(3) 0.000 12(2) 
181Ta 180.947 996(3) 0.999 88(2) 
74W Tungsten (Wolfram) Ar (W) = 183.84(1) [Since 1991] Isotope Atomic mass/u 

180W 179.946 706(5) 0.0012(1) 
182W 181.948 205(3) 0.2650(16) 
183W 182.950 2242(30) 0.1431(4) 
184W 183.950 9323(30) 0.3064(2) 
186W 185.954 362(3) 0.2843(19) 

75Re Rhenium Ar (Re) = 186.207(1) [Since 1975] Isotope Atomic mass/u 

185Re 184.952 955(3) 0.3740(2) 
187Re 186.955 7505(30) 0.6260(2) 

76Os Osmium Ar (Os) = 190.23(3) g [Since 1991] Isotope Atomic mass/u 

184Os 183.952 491(3) 0.0002(1) 
186Os 185.953 838(3) 0.0159(3) 
187Os 186.955 7476(30) 0.0196(2) 
188Os 187.955 8357(30) 0.1324(8) 
189Os 188.958 145(3) 0.1615(5) 
190Os 189.958 445(3) 0.2626(2) 
192Os 191.961 479(4) 0.4078(19) 

77Ir Iridium Ar (Ir) = 192.217(3) [Since 1993] Isotope Atomic mass/u 

191Ir 190.960 591(3) 0.373(2) 
193Ir 192.962 923(3) 0.627(2) 

78Pt Platinum Ar (Pt) = 195.078(2) [Since 1995] Isotope Atomic mass/u 

190Pt 189.959 930(7) 0.000 14(1) 
192Pt 191.961 035(4) 0.007 82(7) 
194Pt 193.962 663(3) 0.329 67(99) 
195Pt 194.964 774(3) 0.338 32(10) 
196Pt 195.964 934(3) 0.252 42(41) 
198Pt 197.967 875(5) 0.071 63(55) 

79Au Gold (Aurum) Ar (Au) = 196.966 55(2) [Since 1995] Isotope Atomic mass/u 

197Au 196.966 551(3) 1.0000 

80Hg Mercury (Hydrargyrum) Ar (Hg) = 200.59(2) [Since 1989] Isotope Atomic mass/u 

196Hg 195.965 814(4) 0.0015(1) 
198Hg 197.966 752(3) 0.0997(20) 
199Hg 198.968 262(3) 0.1687(22) 
200Hg 199.968 309(3) 0.2310(19) 
201Hg 200.970 285(3) 0.1318(9)
202Hg 201.970 625(3) 0.2986(26) 
204Hg 203.973 475(3) 0.0687(15) 

81Tl Thallium Ar (Tl) = 204.3833(2) [Since 1985] Isotope Atomic mass/u 

203Tl 202.972 329(3) 0.2952(1) 
205Tl 204.974 412(3) 0.7048(1) 

82Pb Lead (Plumbum) Ar (Pb) = 207.2(1) g, r [Since 1969] Isotope Atomic mass/u 

204Pb 203.973 028(3) 0.014(1) 
206Pb 205.974 449(3) 0.241(1) 
207Pb 206.975 880(3) 0.221(1) 
208Pb 207.976 636(3) 0.524(1) 

83Bi Bismuth Ar (Bi) = 208.980 38(2) [Since 1995] Isotope Atomic mass/u 

209Bi 208.980 384(3) 1.0000 

90Th Thorium Ar (Th) = 232.0381(1) g [Since 1969] Isotope Atomic mass/u 

232Th 232.038 0495(22) 1.0000 

91Pa Protactinum Ar (Pa) = 231.035 88(2) [Since 1989] Isotope Atomic mass/u 

231Pa 231.035 88(2) 1.0000 

92U Uranium Ar (U) = 238.028 91(3) g, m [Since 1999] Isotope Atomic mass/u 

234U 234.040 9447(22) 0.000 054(5) 
235U 235.043 9222(21) 0.007 204(6) 
238U 238.050 7835(22) 0.992 742(10) 
