Isotopic Abundances

Since 1931, the Commission regularly publishes the critical evaluation of isotopic abundances of elements. These values form basis for the standard atomic weights of elements. Below is the current table of Isotopic Compositions of the Elements.

Isotopic Compositions of the Elements 2024

Z	E	Element	A	Representative isotopic composition	Notes
1	H	hydrogen	1	[0.999 72, 0.999 99]	m
1	H	hydrogen	2	[0.000 01, 0.000 28]	m
2	He	helium	3	0.000 002(2)	g r
2	He	helium	4	0.999 998(2)	g r
3	Li	lithium	6	[0.019, 0.078]	m
3	Li	lithium	7	[0.922, 0.981]	m
4	Be	beryllium	9	1
5	B	boron	10	[0.189, 0.204]	m
5	B	boron	11	[0.796, 0.811]	m
6	C	carbon	12	[0.9884, 0.9904]
6	C	carbon	13	[0.0096, 0.0116]
7	N	nitrogen	14	[0.995 78, 0.996 63]
7	N	nitrogen	15	[0.003 37, 0.004 22]
8	O	oxygen	16	[0.997 38, 0.997 76]
			17	[0.000 367, 0.000 400]
			18	[0.001 87, 0.002 22]
9	F	fluorine	19	1
10	Ne	neon	20	0.9048(3)	g m
			21	0.0027(1)
			22	0.0925(3)
11	Na	sodium	23	1
12	Mg	magnesium	24	[0.7888, 0.7905]
			25	[0.099 88, 0.100 34]
			26	[0.1096, 0.1109]
13	Al	aluminium	27	1
14	Si	silicon	28	[0.921 91, 0.923 18]
			29	[0.046 45, 0.046 99]
			30	[0.030 37, 0.031 10]
15	P	phosphorus	31	1
16	S	sulfur	32	[0.9441, 0.9529]
			33	[0.007 29, 0.007 97]
			34	[0.0396, 0.0477]
			36	[0.000 129, 0.000 187]
17	Cl	chlorine	35	[0.755, 0.761]	m
17	Cl	chlorine	37	[0.239, 0.245]	m
18	Ar	argon	36	[0.0000, 0.0207]	g r
			38	[0.000, 0.043]
			40	[0.936, 1.000]
19	K	potassium	39	0.932 581(44)
			40	0.000 117(1)
			41	0.067 302(44)
20	Ca	calcium	40	0.969 41(156)	g
			42	0.006 47(23)
			43	0.001 35(10)
			44	0.020 86(110)
			46	0.000 04(3)
			48	0.001 87(21)
21	Sc	scandium	45	1
22	Ti	titanium	46	0.0825(3)
			47	0.0744(2)
			48	0.7372(3)
			49	0.0541(2)
			50	0.0518(2)
23	V	vanadium	50	0.002 50(10)
23	V	vanadium	51	0.997 50(10)
24	Cr	chromium	50	0.043 45(13)
			52	0.837 89(18)
			53	0.095 01(17)
			54	0.023 65(7)
25	Mn	manganese	55	1
26	Fe	iron	54	0.058 45(105)
			56	0.917 54(106)
			57	0.021 19(29)
			58	0.002 82(12)
27	Co	cobalt	59	1
28	Ni	nickel	58	0.680 769(190)	r
			60	0.262 231(150)
			61	0.011 399(13)
			62	0.036 345(40)
			64	0.009 256(19)
29	Cu	copper	63	0.6915(15)	r
29	Cu	copper	65	0.3085(15)	r
30	Zn	zinc	64	0.4917(75)	r
			66	0.2773(98)
			67	0.0404(16)
			68	0.1845(63)
			70	0.0061(10)
31	Ga	gallium	69	0.601 08(50)
31	Ga	gallium	71	0.398 92(50)
32	Ge	germanium	70	0.2052(19)
			72	0.2745(15)
			73	0.0776(8)
			74	0.3652(12)
			76	0.0775(12)
33	As	arsenic	75	1
34	Se	selenium	74	0.0086(3)	r
			76	0.0923(7)
			77	0.0760(7)
			78	0.2369(22)
			80	0.4980(36)
			82	0.0882(15)
35	Br	bromine	79	[0.505, 0.508]
35	Br	bromine	81	[0.492, 0.495]
36	Kr	krypton	78	0.003 55(3)	g m
			80	0.022 86(10)
			82	0.115 93(31)
			83	0.115 00(19)
			84	0.569 87(15)
			86	0.172 79(41)
37	Rb	rubidium	85	0.7217(2)	g
37	Rb	rubidium	87	0.2783(2)	g
38	Sr	strontium	84	0.0056(2)	g r
			86	0.0986(20)
			87	0.0700(20)
			88	0.8258(35)
39	Y	yttrium	89	1
40	Zr	zirconium	90	0.5147(6)	g
			91	0.1123(6)
			92	0.1716(4)
			94	0.1736(7)
			96	0.0278(4)
41	Nb	niobium	93	1
42	Mo	molybdenum	92	0.146 49(106)	g
			94	0.091 87(33)
			95	0.158 73(30)
			96	0.166 73(8)
			97	0.095 82(15)
			98	0.242 92(80)
			100	0.097 44(65)
43	Tc	technetium	[97]	-
44	Ru	ruthenium	96	0.0554(14)	g
			98	0.0187(3)
			99	0.1276(14)
			100	0.1260(7)
			101	0.1706(2)
			102	0.3155(14)
			104	0.1862(27)
45	Rh	rhodium	103	1
46	Pd	palladium	102	0.0102(1)	g
			104	0.1114(8)
			105	0.2233(8)
			106	0.2733(3)
			108	0.2646(9)
			110	0.1172(9)
47	Ag	silver	107	0.518 39(8)	g
47	Ag	silver	109	0.481 61(8)	g
48	Cd	cadmium	106	0.012 45(22)	g
			108	0.008 88(11)
			110	0.124 70(61)
			111	0.127 95(12)
			112	0.241 09(7)
			113	0.122 27(7)
			114	0.287 54(81)
			116	0.075 12(54)
49	In	indium	113	0.042 81(52)
49	In	indium	115	0.957 19(52)
50	Sn	tin	112	0.0097(1)	g
			114	0.0066(1)
			115	0.0034(1)
			116	0.1454(9)
			117	0.0768(7)
			118	0.2422(9)
			119	0.0859(4)
			120	0.3258(9)
			122	0.0463(3)
			124	0.0579(5)
51	Sb	antimony	121	0.5721(5)	g
51	Sb	antimony	123	0.4279(5)	g
52	Te	tellurium	120	0.0009(1)	g
			122	0.0255(12)
			123	0.0089(3)
			124	0.0474(14)
			125	0.0707(15)
			126	0.1884(25)
			128	0.3174(8)
			130	0.3408(62)
53	I	iodine	127	1
54	Xe	xenon	124	0.000 95(5)	g m
			126	0.000 89(3)
			128	0.019 10(13)
			129	0.264 01(138)
			130	0.040 71(22)
			131	0.212 32(51)
			132	0.269 09(55)
			134	0.104 36(35)
			136	0.088 57(72)
55	Cs	caesium	133	1
56	Ba	barium	130	0.0011(1)
			132	0.0010(1)
			134	0.0242(15)
			135	0.0659(10)
			136	0.0785(24)
			137	0.1123(23)
			138	0.7170(29)
57	La	lanthanum	138	0.000 8881(71)	g
57	La	lanthanum	139	0.999 1119(71)	g
58	Ce	cerium	136	0.001 85(2)	g
			138	0.002 51(2)
			140	0.884 50(51)
			142	0.111 14(51)
59	Pr	praseodymium	141	1
60	Nd	neodymium	142	0.271 52(40)	g
			143	0.121 74(26)
			144	0.237 98(19)
			145	0.082 93(12)
			146	0.171 89(32)
			148	0.057 56(21)
			150	0.056 38(28)
61	Pm	promethium	[145]	-
62	Sm	samarium	144	0.0308(4)	g
			147	0.1500(14)
			148	0.1125(9)
			149	0.1382(10)
			150	0.0737(9)
			152	0.2674(9)
			154	0.2274(14)
63	Eu	europium	151	0.4781(6)	g
63	Eu	europium	153	0.5219(6)	g
64	Gd	gadolinium	152	0.002 04(2)	g
			154	0.021 87(9)
			155	0.148 28(60)
			156	0.204 93(22)
			157	0.156 57(17)
			158	0.248 20(20)
			160	0.218 11(28)
65	Tb	terbium	159	1
66	Dy	dysprosium	156	0.000 56(3)	g
			158	0.000 95(3)
			160	0.023 29(18)
			161	0.188 89(42)
			162	0.254 75(36)
			163	0.248 96(42)
			164	0.282 60(54)
67	Ho	holmium	165	1
68	Er	erbium	162	0.001 39(5)	g
			164	0.016 01(3)
			166	0.335 03(36)
			167	0.228 69(9)
			168	0.269 78(18)
			170	0.149 10(36)
69	Tm	thulium	169	1
70	Yb	ytterbium	168	0.001 26(1)	g
			170	0.030 23(2)
			171	0.142 16(7)
			172	0.217 54(10)
			173	0.160 98(9)
			174	0.318 96(26)
			176	0.128 87(30)
71	Lu	lutetium	175	0.974 14(5)	g
71	Lu	lutetium	176	0.025 86(5)	g
72	Hf	hafnium	174	0.001 61(2)	g
			176	0.0524(14)
			177	0.1858(9)
			178	0.2728(6)
			179	0.1363(3)
			180	0.3512(16)
73	Ta	tantalum	180	0.000 1176(23)
73	Ta	tantalum	181	0.999 8824(23)
74	W	tungsten	180	0.0012(1)
			182	0.2650(16)
			183	0.1431(4)
			184	0.3064(2)
			186	0.2843(19)
75	Re	rhenium	185	0.3740(5)
75	Re	rhenium	187	0.6260(5)
76	Os	osmium	184	0.0002(2)	g
			186	0.0159(64)
			187	0.0196(17)
			188	0.1324(27)
			189	0.1615(23)
			190	0.2626(20)
			192	0.4078(32)
77	Ir	iridium	191	0.3723(9)
77	Ir	iridium	193	0.6277(9)
78	Pt	platinum	190	0.000 12(2)
			192	0.007 82(24)
			194	0.328 64(410)
			195	0.337 75(240)
			196	0.252 11(340)
			198	0.073 56(130)
79	Au	gold	197	1
80	Hg	mercury	196	0.0015(1)
			198	0.1004(3)
			199	0.1694(12)
			200	0.2314(9)
			201	0.1317(9)
			202	0.2974(13)
			204	0.0682(4)
81	Tl	thallium	203	[0.2944, 0.2959]
81	Tl	thallium	205	[0.7041, 0.7056]
82	Pb	lead	204	[0.0000, 0.0158]
			206	[0.0190, 0.8673]
			207	[0.0035, 0.2351]
			208	[0.0338, 0.9775]
83	Bi	bismuth	209	1
84	Po	polonium	[209]	-
85	At	astatine	[210]	-
86	Rn	radon	[222]	-
87	Fr	francium	[223]	-
88	Ra	radium	[226]	-
89	Ac	actinium	[227]	-
90	Th	thorium	230	0.0002(2)	g
90	Th	thorium	232	0.9998(2)	g
91	Pa	protactinium	231	1
92	U	uranium	234	0.000 054(5)	g m
			235	0.007 204(6)
			238	0.992 742(10)
Z	E	Element	A	Representative isotopic composition	Notes

Footnotes Back to Top
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.
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.

Citation

J. Meija et al
Isotopic compositions of the elements 2013 Pure and Applied Chemistry 88, 293-306 (2016)

This Table can be cited as follows:
CIAAW. Isotopic compositions of the elements 2024. Available online at www.ciaaw.org.

Standard Isotopic Compositions of ytterbium (2015), tantalum (2017), iridium (2017), argon (2017), hafnium (2019), lead(2021), gadolinium (2024), lutetium (2024), and zirconium (2024) have been revised by the CIAAW since the "Isotopic compositions of the elements 2013" Report and these revisions are included in this table.