Abridged Standard Atomic Weights

The Commission does acknowledge that the full Table of Standard Atomic Weights might provide too many details. Abridged standard atomic weights are quoted to five significant figures unless such precision cannot be attained due to the variability of isotopic composition in normal materials or due to the limitations of the measurement capability.

Abridged Standard Atomic Weights 2021

Z	Symbol	Element	Abridged Standard Atomic Weight	Notes
1	H	hydrogen	1.0080 ± 0.0002	m
2	He	helium	4.0026 ± 0.0001	g r
3	Li	lithium	6.94 ± 0.06	m
4	Be	beryllium	9.0122 ± 0.0001
5	B	boron	10.81 ± 0.02	m
6	C	carbon	12.011 ± 0.002
7	N	nitrogen	14.007 ± 0.001	m
8	O	oxygen	15.999 ± 0.001	m
9	F	fluorine	18.998 ± 0.001
10	Ne	neon	20.180 ± 0.001	g m
11	Na	sodium	22.990 ± 0.001
12	Mg	magnesium	24.305 ± 0.002
13	Al	aluminium	26.982 ± 0.001
14	Si	silicon	28.085 ± 0.001
15	P	phosphorus	30.974 ± 0.001
16	S	sulfur	32.06 ± 0.02
17	Cl	chlorine	35.45 ± 0.01	m
18	Ar	argon	39.95 ± 0.16
19	K	potassium	39.098 ± 0.001
20	Ca	calcium	40.078 ± 0.004	g
21	Sc	scandium	44.956 ± 0.001
22	Ti	titanium	47.867 ± 0.001
23	V	vanadium	50.942 ± 0.001
24	Cr	chromium	51.996 ± 0.001
25	Mn	manganese	54.938 ± 0.001
26	Fe	iron	55.845 ± 0.002
27	Co	cobalt	58.933 ± 0.001
28	Ni	nickel	58.693 ± 0.001	r
29	Cu	copper	63.546 ± 0.003	r
30	Zn	zinc	65.38 ± 0.02	r
31	Ga	gallium	69.723 ± 0.001
32	Ge	germanium	72.630 ± 0.008
33	As	arsenic	74.922 ± 0.001
34	Se	selenium	78.971 ± 0.008	r
35	Br	bromine	79.904 ± 0.003
36	Kr	krypton	83.798 ± 0.002	g m
37	Rb	rubidium	85.468 ± 0.001	g
38	Sr	strontium	87.62 ± 0.01	g r
39	Y	yttrium	88.906 ± 0.001
40	Zr	zirconium	91.224 ± 0.002	g
41	Nb	niobium	92.906 ± 0.001
42	Mo	molybdenum	95.95 ± 0.01	g
43	Tc	technetium	—
44	Ru	ruthenium	101.07 ± 0.02	g
45	Rh	rhodium	102.91 ± 0.01
46	Pd	palladium	106.42 ± 0.01	g
47	Ag	silver	107.87 ± 0.01	g
48	Cd	cadmium	112.41 ± 0.01	g
49	In	indium	114.82 ± 0.01
50	Sn	tin	118.71 ± 0.01	g
51	Sb	antimony	121.76 ± 0.01	g
52	Te	tellurium	127.60 ± 0.03	g
53	I	iodine	126.90 ± 0.01
54	Xe	xenon	131.29 ± 0.01	g m
55	Cs	caesium	132.91 ± 0.01
56	Ba	barium	137.33 ± 0.01
57	La	lanthanum	138.91 ± 0.01	g
58	Ce	cerium	140.12 ± 0.01	g
59	Pr	praseodymium	140.91 ± 0.01
60	Nd	neodymium	144.24 ± 0.01	g
61	Pm	promethium	—
62	Sm	samarium	150.36 ± 0.02	g
63	Eu	europium	151.96 ± 0.01	g
64	Gd	gadolinium	157.25 ± 0.03	g
65	Tb	terbium	158.93 ± 0.01
66	Dy	dysprosium	162.50 ± 0.01	g
67	Ho	holmium	164.93 ± 0.01
68	Er	erbium	167.26 ± 0.01	g
69	Tm	thulium	168.93 ± 0.01
70	Yb	ytterbium	173.05 ± 0.02	g
71	Lu	lutetium	174.97 ± 0.01	g
72	Hf	hafnium	178.49 ± 0.01
73	Ta	tantalum	180.95 ± 0.01
74	W	tungsten	183.84 ± 0.01
75	Re	rhenium	186.21 ± 0.01
76	Os	osmium	190.23 ± 0.03	g
77	Ir	iridium	192.22 ± 0.01
78	Pt	platinum	195.08 ± 0.02
79	Au	gold	196.97 ± 0.01
80	Hg	mercury	200.59 ± 0.01
81	Tl	thallium	204.38 ± 0.01
82	Pb	lead	207.2 ± 1.1
83	Bi	bismuth	208.98 ± 0.01
84	Po	polonium	—
85	At	astatine	—
86	Rn	radon	—
87	Fr	francium	—
88	Ra	radium	—
89	Ac	actinium	—
90	Th	thorium	232.04 ± 0.01	g
91	Pa	protactinium	231.04 ± 0.01
92	U	uranium	238.03 ± 0.01	g m
93	Np	neptunium	—
94	Pu	plutonium	—
95	Am	americium	—
96	Cm	curium	—
97	Bk	berkelium	—
98	Cf	californium	—
99	Es	einsteinium	—
100	Fm	fermium	—
101	Md	mendelevium	—
102	No	nobelium	—
103	Lr	lawrencium	—
104	Rf	rutherfordium	—
105	Db	dubnium	—
106	Sg	seaborgium	—
107	Bh	bohrium	—
108	Hs	hassium	—
109	Mt	meitnerium	—
110	Ds	darmstadtium	—
111	Rg	roentgenium	—
112	Cn	copernicium	—
113	Nh	nihonium	—
114	Fl	flerovium	—
115	Mc	moscovium	—
116	Lv	livermorium	—
117	Ts	tennessine	—
118	Og	oganesson	—
Z	Symbol	Element	Abridged Standard Atomic Weight	Notes

Footnotes Back to Top
g Geological 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 an undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.
r Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated atomic-weight value and uncertainty should be applicable to normal materials.

Citation

The most recent Standard Atomic Weights are presented in this Table and they are based on the "Atomic Weights 2021" report.

In 2013, the Commission recommended that standard atomic weights are best abridged to five digits.