Values based on the 1999 table Pure Appl. Chem., 73, 667-683 (2001) and changes reported from the 2001 review in Chem. Int., 23, 179 (2001). The values of zinc, krypton, molybdenum and dysprosium have been modified.
World Wide Web version of atomic weight data prepared by G. P. Moss, originally from a file provided by D. R. Lide.
Note The claim [Phys. Rev. Lett. 1999, 83, 1104] for elements 116 and 118 has been withdrawn [see Chem. Eng. News 2001, 79, 10 (6 August 2001); 2002, 80, 12 (22 July 2002);Phys. Rev. Lett. 2002, 89, 039901]
Previous values may be consulted from the 1993 table, the 1995 table, 1997 table or 1999 table.
The original paper should be consulted for details of the half life of the radioisotopes quoted below. In addition there are recommendations on the scales for quoting relative isotope-ratio data for stable hydrogen, lithium, carbon, oxygen and sulfur. Also there is a report on the different isotopic compositions of some non-terrestrial materials.
A number in parentheses indicates the uncertainty in the last digit of the atomic weight.
See also a copy of the periodic table with atomic weights to five significant figures.
See also below the list in Name order.
At No | Symbol | Name | Atomic Wt | Notes |
1 | H | Hydrogen | 1.00794(7) | 1, 2, 3 |
2 | He | Helium | 4.002602(2) | 1, 2 |
3 | Li | Lithium | [6.941(2)] | 1, 2, 3, 4 |
4 | Be | Beryllium | 9.012182(3) | |
5 | B | Boron | 10.811(7) | 1, 2, 3 |
6 | C | Carbon | 12.0107(8) | 1, 2 |
7 | N | Nitrogen | 14.0067(2) | 1, 2 |
8 | O | Oxygen | 15.9994(3) | 1, 2 |
9 | F | Fluorine | 18.9984032(5) | |
10 | Ne | Neon | 20.1797(6) | 1, 3 |
11 | Na | Sodium | 22.989770(2) | |
12 | Mg | Magnesium | 24.3050(6) | |
13 | Al | Aluminium | 26.981538(2) | |
14 | Si | Silicon | 28.0855(3) | 2 |
15 | P | Phosphorus | 30.973761(2) | |
16 | S | Sulfur | 32.065(5) | 1, 2 |
17 | Cl | Chlorine | 35.453(2) | 3 |
18 | Ar | Argon | 39.948(1) | 1, 2 |
19 | K | Potassium | 39.0983(1) | 1 |
20 | Ca | Calcium | 40.078(4) | 1 |
21 | Sc | Scandium | 44.955910(8) | |
22 | Ti | Titanium | 47.867(1) | |
23 | V | Vanadium | 50.9415(1) | |
24 | Cr | Chromium | 51.9961(6) | |
25 | Mn | Manganese | 54.938049(9) | |
26 | Fe | Iron | 55.845(2) | |
27 | Co | Cobalt | 58.933200(9) | |
28 | Ni | Nickel | 58.6934(2) | |
29 | Cu | Copper | 63.546(3) | 2 |
30 | Zn | Zinc | 65.409(4) | |
31 | Ga | Gallium | 69.723(1) | |
32 | Ge | Germanium | 72.64(1) | |
33 | As | Arsenic | 74.92160(2) | |
34 | Se | Selenium | 78.96(3) | |
35 | Br | Bromine | 79.904(1) | |
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 | 88.90585(2) | |
40 | Zr | Zirconium | 91.224(2) | 1 |
41 | Nb | Niobium | 92.90638(2) | |
42 | Mo | Molybdenum | 95.94(2) | 1 |
43 | Tc | Technetium | [98] | 5 |
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 | 112.411(8) | 1 |
49 | In | Indium | 114.818(3) | |
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 | 132.90545(2) | |
56 | Ba | Barium | 137.327(7) | |
57 | La | Lanthanum | 138.9055(2) | 1 |
58 | Ce | Cerium | 140.116(1) | 1 |
59 | Pr | Praseodymium | 140.90765(2) | |
60 | Nd | Neodymium | 144.24(3) | 1 |
61 | Pm | Promethium | [145] | 5 |
62 | Sm | Samarium | 150.36(3) | 1 |
63 | Eu | Europium | 151.964(1) | 1 |
64 | Gd | Gadolinium | 157.25(3) | 1 |
65 | Tb | Terbium | 158.92534(2) | |
66 | Dy | Dysprosium | 162.500(1) | 1 |
67 | Ho | Holmium | 164.93032(2) | |
68 | Er | Erbium | 167.259(3) | 1 |
69 | Tm | Thulium | 168.93421(2) | |
70 | Yb | Ytterbium | 173.04(3) | 1 |
71 | Lu | Lutetium | 174.967(1) | 1 |
72 | Hf | Hafnium | 178.49(2) | |
73 | Ta | Tantalum | 180.9479(1) | |
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 | 195.078(2) | |
79 | Au | Gold | 196.96655(2) | |
80 | Hg | Mercury | 200.59(2) | |
81 | Tl | Thallium | 204.3833(2) | |
82 | Pb | Lead | 207.2(1) | 1, 2 |
83 | Bi | Bismuth | 208.98038(2) | |
84 | Po | Polonium | [209] | 5 |
85 | At | Astatine | [210] | 5 |
86 | Rn | Radon | [222] | 5 |
87 | Fr | Francium | [223] | 5 |
88 | Ra | Radium | [226] | 5 |
89 | Ac | Actinium | [227] | 5 |
90 | Th | Thorium | 232.0381(1) | 1, 5 |
91 | Pa | Protactinium | 231.03588(2) | 5 |
92 | U | Uranium | 238.02891(3) | 1, 3, 5 |
93 | Np | Neptunium | [237] | 5 |
94 | Pu | Plutonium | [244] | 5 |
95 | Am | Americium | [243] | 5 |
96 | Cm | Curium | [247] | 5 |
97 | Bk | Berkelium | [247] | 5 |
98 | Cf | Californium | [251] | 5 |
99 | Es | Einsteinium | [252] | 5 |
100 | Fm | Fermium | [257] | 5 |
101 | Md | Mendelevium | [258] | 5 |
102 | No | Nobelium | [259] | 5 |
103 | Lr | Lawrencium | [262] | 5 |
104 | Rf | Rutherfordium | [261] | 5, 6 |
105 | Db | Dubnium | [262] | 5, 6 |
106 | Sg | Seaborgium | [266] | 5, 6 |
107 | Bh | Bohrium | [264] | 5, 6 |
108 | Hs | Hassium | [277] | 5, 6 |
109 | Mt | Meitnerium | [268] | 5, 6 |
110 | Uun | Ununnilium | [281] | 5, 6 |
111 | Uuu | Unununium | [272] | 5, 6 |
112 | Uub | Ununbium | [285] | 5, 6 |
114 | Uuq | Ununquadium | [289] | 5, 6 |
116 | Uuh | Ununhexium | see Note above | |
118 | Uuo | Ununoctium | see Note above |
At No | Symbol | Name | Atomic Wt | Notes |
89 | Ac | Actinium | [227] | 5 |
13 | Al | Aluminium | 26.981538(2) | |
95 | Am | Americium | [243] | 5 |
51 | Sb | Antimony | 121.760(1) | 1 |
18 | Ar | Argon | 39.948(1) | 1, 2 |
33 | As | Arsenic | 74.92160(2) | |
85 | At | Astatine | [210] | 5 |
56 | Ba | Barium | 137.327(7) | |
97 | Bk | Berkelium | [247] | 5 |
4 | Be | Beryllium | 9.012182(3) | |
83 | Bi | Bismuth | 208.98038(2) | |
107 | Bh | Bohrium | [264] | 5, 6 |
5 | B | Boron | 10.811(7) | 1, 2, 3 |
35 | Br | Bromine | 79.904(1) | |
48 | Cd | Cadmium | 112.411(8) | 1 |
55 | Cs | Caesium | 132.90545(2) | |
20 | Ca | Calcium | 40.078(4) | 1 |
98 | Cf | Californium | [251] | 5 |
6 | C | Carbon | 12.0107(8) | 1, 2 |
58 | Ce | Cerium | 140.116(1) | 1 |
17 | Cl | Chlorine | 35.453(2) | 3 |
24 | Cr | Chromium | 51.9961(6) | |
27 | Co | Cobalt | 58.933200(9) | |
29 | Cu | Copper | 63.546(3) | 2 |
96 | Cm | Curium | [247] | 5 |
105 | Db | Dubnium | [262] | 5, 6 |
66 | Dy | Dysprosium | 162.500(1) | 1 |
99 | Es | Einsteinium | [252] | 5 |
68 | Er | Erbium | 167.259(3) | 1 |
63 | Eu | Europium | 151.964(1) | 1 |
100 | Fm | Fermium | [257] | 5 |
9 | F | Fluorine | 18.9984032(5) | |
87 | Fr | Francium | [223] | 5 |
64 | Gd | Gadolinium | 157.25(3) | 1 |
31 | Ga | Gallium | 69.723(1) | |
32 | Ge | Germanium | 72.64(1) | |
79 | Au | Gold | 196.96655(2) | |
72 | Hf | Hafnium | 178.49(2) | |
108 | Hs | Hassium | [277] | 5, 6 |
2 | He | Helium | 4.002602(2) | 1, 2 |
67 | Ho | Holmium | 164.93032(2) | |
1 | H | Hydrogen | 1.00794(7) | 1, 2, 3 |
49 | In | Indium | 114.818(3) | |
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 | 138.9055(2) | 1 |
103 | Lr | Lawrencium | [262] | 5 |
82 | Pb | Lead | 207.2(1) | 1, 2 |
3 | Li | Lithium | [6.941(2)] | 1, 2, 3, 4 |
71 | Lu | Lutetium | 174.967(1) | 1 |
12 | Mg | Magnesium | 24.3050(6) | |
25 | Mn | Manganese | 54.938049(9) | |
109 | Mt | Meitnerium | [268] | 5, 6 |
101 | Md | Mendelevium | [258] | 5 |
80 | Hg | Mercury | 200.59(2) | |
42 | Mo | Molybdenum | 95.94(2) | 1 |
60 | Nd | Neodymium | 144.24(3) | 1 |
10 | Ne | Neon | 20.1797(6) | 1, 3 |
93 | Np | Neptunium | [237] | 5 |
28 | Ni | Nickel | 58.6934(2) | |
41 | Nb | Niobium | 92.90638(2) | |
7 | N | Nitrogen | 14.0067(2) | 1, 2 |
102 | No | Nobelium | [259] | 5 |
76 | Os | Osmium | 190.23(3) | 1 |
8 | O | Oxygen | 15.9994(3) | 1, 2 |
46 | Pd | Palladium | 106.42(1) | 1 |
15 | P | Phosphorus | 30.973761(2) | |
78 | Pt | Platinum | 195.078(2) | |
94 | Pu | Plutonium | [244] | 5 |
84 | Po | Polonium | [209] | 5 |
19 | K | Potassium | 39.0983(1) | 1 |
59 | Pr | Praseodymium | 140.90765(2) | |
61 | Pm | Promethium | [145] | 5 |
91 | Pa | Protactinium | 231.03588(2) | 5 |
88 | Ra | Radium | [226] | 5 |
86 | Rn | Radon | [222] | 5 |
75 | Re | Rhenium | 186.207(1) | |
45 | Rh | Rhodium | 102.90550(2) | |
37 | Rb | Rubidium | 85.4678(3) | 1 |
44 | Ru | Ruthenium | 101.07(2) | 1 |
104 | Rf | Rutherfordium | [261] | 5, 6 |
62 | Sm | Samarium | 150.36(3) | 1 |
21 | Sc | Scandium | 44.955910(8) | |
106 | Sg | Seaborgium | [266] | 5, 6 |
34 | Se | Selenium | 78.96(3) | |
14 | Si | Silicon | 28.0855(3) | 2 |
47 | Ag | Silver | 107.8682(2) | 1 |
11 | Na | Sodium | 22.989770(2) | |
38 | Sr | Strontium | 87.62(1) | 1, 2 |
16 | S | Sulfur | 32.065(5) | 1, 2 |
73 | Ta | Tantalum | 180.9479(1) | |
43 | Tc | Technetium | [98] | 5 |
52 | Te | Tellurium | 127.60(3) | 1 |
65 | Tb | Terbium | 158.92534(2) | |
81 | Tl | Thallium | 204.3833(2) | |
90 | Th | Thorium | 232.0381(1) | 1, 5 |
69 | Tm | Thulium | 168.93421(2) | |
50 | Sn | Tin | 118.710(7) | 1 |
22 | Ti | Titanium | 47.867(1) | |
74 | W | Tungsten | 183.84(1) | |
112 | Uub | Ununbium | [285] | 5, 6 |
116 | Uuh | Ununhexium | see Note above | |
110 | Uun | Ununnilium | [281] | 5, 6 |
118 | Uuo | Ununoctium | see Note above | |
114 | Uuq | Ununquadium | [289] | 5, 6 |
111 | Uuu | Unununium | [272] | 5, 6 |
92 | U | Uranium | 238.02891(3) | 1, 3, 5 |
23 | V | Vanadium | 50.9415(1) | |
54 | Xe | Xenon | 131.293(6) | 1, 3 |
70 | Yb | Ytterbium | 173.04(3) | 1 |
39 | Y | Yttrium | 88.90585(2) | |
30 | Zn | Zinc | 65.409(4) | |
40 | Zr | Zirconium | 91.224(2) | 1 |