These tables are based on the 2011 table at Pure Appl. Chem., 2013, 85, 1047-1078 with changes from for the values of aluminium, arsenic, beryllium, cadmium, caesium, cobalt, fluorine, gold, holmium, manganese, molybdenum, niobium, phosphorus, praseodymium, scandium, selenium, thorium, thulium and yttrium [see ciaaw or IUPAC website or Chem. Int. 2013, 35(6), 17-18]. For the 2015 table the atomic weight of ytterbium has been revised [see ciaaw or Chem. Eng. News, 2015, 93(37), 9].
The discovery of elements 113, 115, 117 and 118 have been verified by IUPAC.
https://iupac.qmul.ac.uk/AtWt/
A PDF format copy (1647 KBt) of the 2011 table is available from the abstract
World Wide Web version of atomic weight data originally prepared by G. P. Moss, from a file provided by D. R. Lide.
Previous values may be consulted from the 1993 table, the 1995 table, the 1997 table, the 1999 table, the 2001 table, the 2005 table, the 2007 table, the 2009 table or the 2011 table.
The standard atomic weights of twelve elements having two or more stable isotopes have variability of atomic-weight values in natural terrestrial materials. These are given in table 1 below. In the other lists the values quoted are those suggested for material where the origin of the sample is unknown. For radioactive elements the isotope with the longest half-life is quoted in parenthesis. The original paper should be consulted for full details of the variation in atomic weight and the half life of the radioisotopes quoted below.
A number in parentheses indicates the uncertainty in the last digit of the atomic weight.
See below for the elements listed in Atomic Number Order or Name order.
See also a copy of the periodic table with atomic weights to five significant figures.
At No | Symbol | Name | Minimum Atomic Wt | Maximum Atomic Wt |
1 | H | hydrogen | 1.007 84 | 1.008 11 |
3 | Li | lithium | 6.938 | 6.997 |
5 | B | boron | 10.806 | 10.821 |
6 | C | carbon | 12.0096 | 12.0116 |
7 | N | nitrogen | 14.006 43 | 14.007 28 |
8 | O | oxygen | 15.999 03 | 15.999 77 |
12 | Mg | magnesium | 24.30 | 24.31 |
14 | Si | silicon | 28.084 | 28.086 |
16 | S | sulfur | 32.059 | 32.076 |
17 | Cl | chlorine | 35.446 | 35.457 |
35 | Br | bromine | 79.90 | 79.91 |
81 | Tl | thallium | 204.382 | 204.385 |
See original paper for the range of these elements from different sources.
At No | Symbol | Name | Atomic Wt | Notes |
1 | H | Hydrogen | 1.008 | 3, 6 |
2 | He | Helium | 4.002602(2) | 1, 2 |
3 | Li | Lithium | 6.94 | 3, 6 |
4 | Be | Beryllium | 9.0121831(5) | |
5 | B | Boron | 10.81 | 3, 6 |
6 | C | Carbon | 12.011 | 6 |
7 | N | Nitrogen | 14.007 | 6 |
8 | O | Oxygen | 15.999 | 6 |
9 | F | Fluorine | 18.998403163(6) | |
10 | Ne | Neon | 20.1797(6) | 1, 3 |
11 | Na | Sodium | 22.98976928(2) | |
12 | Mg | Magnesium | 24.305 | 6 |
13 | Al | Aluminium | 26.9815385(7) | |
14 | Si | Silicon | 28.085 | 6 |
15 | P | Phosphorus | 30.973761998(5) | |
16 | S | Sulfur | 32.06 | 6 |
17 | Cl | Chlorine | 35.45 | 3, 6 |
18 | Ar | Argon | 39.948(1) | 1, 2 |
19 | K | Potassium | 39.0983(1) | |
20 | Ca | Calcium | 40.078(4) | |
21 | Sc | Scandium | 44.955908(5) | |
22 | Ti | Titanium | 47.867(1) | |
23 | V | Vanadium | 50.9415(1) | |
24 | Cr | Chromium | 51.9961(6) | |
25 | Mn | Manganese | 54.938044(3) | |
26 | Fe | Iron | 55.845(2) | |
27 | Co | Cobalt | 58.933194(4) | |
28 | Ni | Nickel | 58.6934(4) | 2 |
29 | Cu | Copper | 63.546(3) | 2 |
30 | Zn | Zinc | 65.38(2) | 2 |
31 | Ga | Gallium | 69.723(1) | |
32 | Ge | Germanium | 72.630(8) | |
33 | As | Arsenic | 74.921595(6) | |
34 | Se | Selenium | 78.971(8) | |
35 | Br | Bromine | 79.904 | 6 |
36 | Kr | Krypton | 83.798(2) | 1, 3 |
37 | Rb | Rubidium | 85.4678(3) | 1 |
38 | Sr | Strontium | 87.62(1) | 1, 2 |
39 | Y | Yttrium | 88.90584(2) | |
40 | Zr | Zirconium | 91.224(2) | 1 |
41 | Nb | Niobium | 92.90637(2) | |
42 | Mo | Molybdenum | 95.95(1) | 1 |
43 | Tc | Technetium | [97] | 4 |
44 | Ru | Ruthenium | 101.07(2) | 1 |
45 | Rh | Rhodium | 102.90550(2) | |
46 | Pd | Palladium | 106.42(1) | 1 |
47 | Ag | Silver | 107.8682(2) | 1 |
48 | Cd | Cadmium | 112.414(4) | 1 |
49 | In | Indium | 114.818(1) | |
50 | Sn | Tin | 118.710(7) | 1 |
51 | Sb | Antimony | 121.760(1) | 1 |
52 | Te | Tellurium | 127.60(3) | 1 |
53 | I | Iodine | 126.90447(3) | |
54 | Xe | Xenon | 131.293(6) | 1, 3 |
55 | Cs | Caesium | 132.90545196(6) | |
56 | Ba | Barium | 137.327(7) | |
57 | La | Lanthanum | 138.90547(7) | 1 |
58 | Ce | Cerium | 140.116(1) | 1 |
59 | Pr | Praseodymium | 140.90766(2) | |
60 | Nd | Neodymium | 144.242(3) | 1 |
61 | Pm | Promethium | [145] | 5 |
62 | Sm | Samarium | 150.36(2) | 1 |
63 | Eu | Europium | 151.964(1) | 1 |
64 | Gd | Gadolinium | 157.25(3) | 1 |
65 | Tb | Terbium | 158.92535(2) | |
66 | Dy | Dysprosium | 162.500(1) | 1 |
67 | Ho | Holmium | 164.93033(2) | |
68 | Er | Erbium | 167.259(3) | 1 |
69 | Tm | Thulium | 168.93422(2) | |
70 | Yb | Ytterbium | 173.045(5) | 1 |
71 | Lu | Lutetium | 174.9668(1) | 1 |
72 | Hf | Hafnium | 178.49(2) | |
73 | Ta | Tantalum | 180.94788(2) | |
74 | W | Tungsten | 183.84(1) | |
75 | Re | Rhenium | 186.207(1) | |
76 | Os | Osmium | 190.23(3) | 1 |
77 | Ir | Iridium | 192.217(3) | |
78 | Pt | Platinum | 195.084(9) | |
79 | Au | Gold | 196.966569(5) | |
80 | Hg | Mercury | 200.592(3) | |
81 | Tl | Thallium | 204.38 | 6 |
82 | Pb | Lead | 207.2(1) | 1, 2 |
83 | Bi | Bismuth | 208.98040(1) | |
84 | Po | Polonium | [209] | 4 |
85 | At | Astatine | [210] | 4 |
86 | Rn | Radon | [222] | 4 |
87 | Fr | Francium | [223] | 4 |
88 | Ra | Radium | [226] | 4 |
89 | Ac | Actinium | [227] | 4 |
90 | Th | Thorium | 232.0377(4) | 1, 4 |
91 | Pa | Protactinium | 231.03588(2) | 4 |
92 | U | Uranium | 238.02891(3) | 1, 3, 4 |
93 | Np | Neptunium | [237] | 4 |
94 | Pu | Plutonium | [244] | 4 |
95 | Am | Americium | [243] | 4 |
96 | Cm | Curium | [247] | 4 |
97 | Bk | Berkelium | [247] | 4 |
98 | Cf | Californium | [251] | 4 |
99 | Es | Einsteinium | [252] | 4 |
100 | Fm | Fermium | [257] | 4 |
101 | Md | Mendelevium | [258] | 4 |
102 | No | Nobelium | [259] | 4 |
103 | Lr | Lawrencium | [262] | 4 |
104 | Rf | Rutherfordium | [267] | 4 |
105 | Db | Dubnium | [270] | 4 |
106 | Sg | Seaborgium | [271] | 4 |
107 | Bh | Bohrium | [270] | 4 |
108 | Hs | Hassium | [277] | 4 |
109 | Mt | Meitnerium | [276] | 4 |
110 | Ds | Darmstadtium | [281] | 4 |
111 | Rg | Roentgenium | [282] | 4 |
112 | Cn | Copernicium | [285] | 4 |
113 | Uut | Ununtrium | [285] | 4, 5 |
114 | Fl | Flerovium | [289] | 4, 5 |
115 | Uup | Ununpentium | [289] | 4, 5 |
116 | Lv | Livermorium | [293] | 4, 5 |
117 | Uus | Ununseptium | [294] | 4, 5 |
118 | Uuo | Ununoctium | [294] | 4, 5 |
At No | Symbol | Name | Atomic Wt | Notes |
89 | Ac | Actinium | [227] | 4 |
13 | Al | Aluminium | 26.9815385(7) | |
95 | Am | Americium | [243] | 4 |
51 | Sb | Antimony | 121.760(1) | 1 |
18 | Ar | Argon | 39.948(1) | 1, 2 |
33 | As | Arsenic | 74.921595(6) | |
85 | At | Astatine | [210] | 4 |
56 | Ba | Barium | 137.327(7) | |
97 | Bk | Berkelium | [247] | 4 |
4 | Be | Beryllium | 9.0121831(5) | |
83 | Bi | Bismuth | 208.98040(1) | |
107 | Bh | Bohrium | [270] | 4 |
5 | B | Boron | 10.81 | 3, 6 |
35 | Br | Bromine | 79.904 | 6 |
48 | Cd | Cadmium | 112.414(4) | 1 |
55 | Cs | Caesium | 132.90545196(6) | |
20 | Ca | Calcium | 40.078(4) | 1 |
98 | Cf | Californium | [251] | 4 |
6 | C | Carbon | 12.011 | 6 |
58 | Ce | Cerium | 140.116(1) | 1 |
17 | Cl | Chlorine | 35.45 | 3, 6 |
24 | Cr | Chromium | 51.9961(6) | |
27 | Co | Cobalt | 58.933194(4) | |
112 | Cn | Copernicium | [285] | 4 |
29 | Cu | Copper | 63.546(3) | 2 |
96 | Cm | Curium | [247] | 4 |
110 | Ds | Darmstadtium | [281] | 4 |
105 | Db | Dubnium | [270] | 4 |
66 | Dy | Dysprosium | 162.500(1) | 1 |
99 | Es | Einsteinium | [252] | 4 |
68 | Er | Erbium | 167.259(3) | 1 |
63 | Eu | Europium | 151.964(1) | 1 |
100 | Fm | Fermium | [257] | 4 |
114 | Fl | Flerovium | [289] | 4, 5 |
9 | F | Fluorine | 18.998403163(6) | |
87 | Fr | Francium | [223] | 4 |
64 | Gd | Gadolinium | 157.25(3) | 1 |
31 | Ga | Gallium | 69.723(1) | |
32 | Ge | Germanium | 72.630(8) | |
79 | Au | Gold | 196.966569(5) | |
72 | Hf | Hafnium | 178.49(2) | |
108 | Hs | Hassium | [277] | 4 |
2 | He | Helium | 4.002602(2) | 1, 2 |
67 | Ho | Holmium | 164.93033(2) | |
1 | H | Hydrogen | 1.008 | 3, 6 |
49 | In | Indium | 114.818(1) | |
53 | I | Iodine | 126.90447(3) | |
77 | Ir | Iridium | 192.217(3) | |
26 | Fe | Iron | 55.845(2) | |
36 | Kr | Krypton | 83.798(2) | 1, 3 |
57 | La | Lanthanum | 138.90547(7) | 1 |
103 | Lr | Lawrencium | [262] | 4 |
82 | Pb | Lead | 207.2(1) | 1, 2 |
3 | Li | Lithium | 6.94 | 3, 6 |
116 | Lv | Livermorium | [293] | 4, 5 |
71 | Lu | Lutetium | 174.9668(1) | 1 |
12 | Mg | Magnesium | 24.305 | 6 |
25 | Mn | Manganese | 54.938044(3) | |
109 | Mt | Meitnerium | [276] | 4 |
101 | Md | Mendelevium | [258] | 4 |
80 | Hg | Mercury | 200.592(3) | |
42 | Mo | Molybdenum | 95.95(1) | 1 |
60 | Nd | Neodymium | 144.242(3) | 1 |
10 | Ne | Neon | 20.1797(6) | 1, 3 |
93 | Np | Neptunium | [237] | 4 |
28 | Ni | Nickel | 58.6934(4) | |
41 | Nb | Niobium | 92.90637(2) | |
7 | N | Nitrogen | 14.007 | 6 |
102 | No | Nobelium | [259] | 4 |
76 | Os | Osmium | 190.23(3) | 1 |
8 | O | Oxygen | 15.999 | 6 |
46 | Pd | Palladium | 106.42(1) | 1 |
15 | P | Phosphorus | 30.973761998(5) | |
78 | Pt | Platinum | 195.084(9) | |
94 | Pu | Plutonium | [244] | 4 |
84 | Po | Polonium | [209] | 4 |
19 | K | Potassium | 39.0983(1) | |
59 | Pr | Praseodymium | 140.90766(2) | |
61 | Pm | Promethium | [145] | 4 |
91 | Pa | Protactinium | 231.03588(2) | 4 |
88 | Ra | Radium | [226] | 4 |
86 | Rn | Radon | [222] | 4 |
75 | Re | Rhenium | 186.207(1) | |
45 | Rh | Rhodium | 102.90550(2) | |
111 | Rg | Roentgenium | [282] | 4 |
37 | Rb | Rubidium | 85.4678(3) | 1 |
44 | Ru | Ruthenium | 101.07(2) | 1 |
104 | Rf | Rutherfordium | [267] | 4 |
62 | Sm | Samarium | 150.36(2) | 1 |
21 | Sc | Scandium | 44.955908(5) | |
106 | Sg | Seaborgium | [271] | 4 |
34 | Se | Selenium | 78.971(8) | |
14 | Si | Silicon | 28.085 | 6 |
47 | Ag | Silver | 107.8682(2) | 1 |
11 | Na | Sodium | 22.98976928(2) | |
38 | Sr | Strontium | 87.62(1) | 1, 2 |
16 | S | Sulfur | 32.06 | 6 |
73 | Ta | Tantalum | 180.94788(2) | |
43 | Tc | Technetium | [97] | 4 |
52 | Te | Tellurium | 127.60(3) | 1 |
65 | Tb | Terbium | 158.92535(2) | |
81 | Tl | Thallium | 204.38 | 6 |
90 | Th | Thorium | 232.0377(4) | 1, 4 |
69 | Tm | Thulium | 168.93422(2) | |
50 | Sn | Tin | 118.710(7) | 1 |
22 | Ti | Titanium | 47.867(1) | |
74 | W | Tungsten | 183.84(1) | |
118 | Uuo | Ununoctium | [294] | 4, 5 |
115 | Uup | Ununpentium | [289] | 4, 5 |
117 | Uus | Ununseptium | [294] | 4, 5 |
113 | Uut | Ununtrium | [285] | 4, 5 |
92 | U | Uranium | 238.02891(3) | 1, 3, 4 |
23 | V | Vanadium | 50.9415(1) | |
54 | Xe | Xenon | 131.293(6) | 1, 3 |
70 | Yb | Ytterbium | 173.045(5) | 1 |
39 | Y | Yttrium | 88.90584(2) | |
30 | Zn | Zinc | 65.38(2) | 2 |
40 | Zr | Zirconium | 91.224(2) | 1 |