Current Table of Standard Atomic Weights Abridged to Four Significant Digits

Atomic weights of the elements 2009, Wieser, M. E., and Coplen, T. B., Pure Appl. Chem., 83, 359–396 (2011). [full text - pdf 1.8 MB] {TSAW 2009.pdf}

Table of Standard Atomic Weights Abridged to Four Significant Digits
[Using A_r(¹²C) = 12 as reference, where ¹²C is an unbound neutral atom in its nuclear and electronic ground state.]

The atomic weights of many elements are not invariant, but depend on the origin and treatment of the material. The standard values of A_r(E) and the uncertainties (in parentheses, following the last significant figure to which they are attributed) apply to elements of natural terrestrial origin. The last significant figure of each tabulated value is considered reliable to ±1 except when a larger single digit uncertainty is inserted in parentheses following the atomic weight. For 10 of these elements, an atomic-weight interval is given with the symbol [a; b] to denote the set of atomic-weight values in normal materials; thus, a ≤ A_r(E) ≤ b for element E. The symbols a and b denote the lower and upper bounds of the interval [a; b], respectively. For more detailed information, users should refer to the full IUPAC Table of Standard Atomic Weights. Names of elements with atomic number 113 to 118 are provisional.

Atomic Number	Element Name	Symbol	Atomic Weight
1	hydrogen	H	[1.007; 1.009]
2	helium	He	4.003
3	lithium	Li	[6.938; 6.997]
4	beryllium	Be	9.012
5	boron	B	[10.80; 10.83]
6	carbon	C	[12.00; 12.02]
7	nitrogen	N	[14.00; 14.01]
8	oxygen	O	[15.99; 16.00]
9	fluorine	F	19.00
10	neon	Ne	20.18
11	sodium	Na	22.99
12	magnesium	Mg	24.31
13	aluminium (aluminum)	Al	26.98
14	silicon	Si	[28.08; 28.09]
15	phosphorus	P	30.97
16	sulfur	S	[32.05; 32.08]
17	chlorine	Cl	[35.44; 35.46]
18	argon	Ar	39.95
19	potassium	K	39.10
20	calcium	Ca	40.08#
21	scandium	Sc	44.96
22	titanium	Ti	47.87
23	vanadium	V	50.94
24	chromium	Cr	52.00
25	manganese	Mn	54.94
26	iron	Fe	55.85
27	cobalt	Co	58.93
28	nickel	Ni	58.69
29	copper	Cu	63.55
30	zinc	Zn	65.38(2)
31	gallium	Ga	69.72
32	germanium	Ge	72.63
33	arsenic	As	74.92
34	selenium	Se	78.96(3)
35	bromine	Br	79.90
36	krypton	Kr	83.80#
37	rubidium	Rb	85.47#
38	strontium	Sr	87.62#
39	yttrium	Y	88.91
40	zirconium	Zr	91.22#
41	niobium	Nb	92.91
42	molybdenum	Mo	95.96(2)#
43	technetium*	Tc
44	ruthenium	Ru	101.1#
45	rhodium	Rh	102.9
46	palladium	Pd	106.4#
47	silver	Ag	107.9#
48	cadmium	Cd	112.4#
49	indium	In	114.8
50	tin	Sn	118.7#
51	antimony	Sb	121.8#
52	tellurium	Te	127.6#
53	iodine	I	126.9
54	xenon	Xe	131.3#
55	caesium (cesium)	Cs	132.9
56	barium	Ba	137.3
57	lanthanum	La	138.9
58	cerium	Ce	140.1#
59	praseodymium	Pr	140.9
60	neodymium	Nd	144.2#
61	promethium*	Pm
62	samarium	Sm	150.4#
63	europium	Eu	152.0#
64	gadolinium	Gd	157.3#
65	terbium	Tb	158.9
66	dysprosium	Dy	162.5#
67	holmium	Ho	164.9
68	erbium	Er	167.3#
69	thulium	Tm	168.9
70	ytterbium	Yb	173.1#
71	lutetium	Lu	175.0
72	hafnium	Hf	178.5
73	tantalum	Ta	180.9
74	tungsten	W	183.8
75	rhenium	Re	186.2
76	osmium	Os	190.2
77	iridium	Ir	192.2
78	platinum	Pt	195.1
79	gold	Au	197.0
80	mercury	Hg	200.6
81	thallium	Tl	[204.3; 204.4]
82	lead	Pb	207.2
83	bismuth	Bi	209.0#
84	polonium*	Po
85	astatine*	At
86	radon*	Rn
87	francium*	Fr
88	radium*	Ra
89	actinium*	Ac
90	thorium*	Th	232.0
91	protactinium*	Pa	231.0
92	uranium*	U	238.0#
93	neptunium*	Np
94	plutonium*	Pu
95	americium*	Am
96	curium*	Cm
97	berkelium*	Bk
98	californium*	Cf
99	einsteinium*	Es
100	fermium*	Fm
101	mendelevium*	Md
102	nobelium*	No
103	lawrencium*	Lr
104	rutherfordium*	Rf
105	dubnium*	Db
106	seaborgium*	Sg
107	bohrium*	Bh
108	hassium*	Hs
109	meitnerium*	Mt
110	darmstadtium*	Ds
111	roentgenium*	Rg
112	copernicium*	Cn
113	ununtrium*	Uut
114	ununquadium*	Uuq
115	ununpentium*	Uup
116	ununhexium*	Uuh
118	ununoctium*	Uuo

*Element has no stable isotopes. However, three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.

# Values may differ from the atomic weights of the relevant elements in some naturally occurring samples because of a variation in the isotopic abundances of the element’s stable isotopes.

2010 Commission on Isotopic Abundances and Atomic Weights | a commission of the International Union of Pure and Applied Chemistry