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Atomic Weights of the Elements

IUPAC List of Atomic Weights

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The periodic table lists the atomic weight of each element.

The periodic table lists the atomic weight of each element.

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This is the 2013 list of atomic weights of the elements in increasing atomic number, as accepted by the IUPAC. The table is based on the "Standard Atomic Weights Revised v2" (Sept 24,2013). The list includes the 2013 changes to the atomic weights of 19 elements: arsenic, beryllium, cadmium, cesium, cobalt, fluorine, gold, holmium, manganese, molybdenum, niobium, phosphorus, praseodymium, scandium, selenium, thorium, thulium and yttrium.


These values remain current until the IUPAC sees the need to revise them.

Values given by the [a;b] notation highlights the range of atomic weights for the element. For these elements, the atomic weight is dependent on the physical and chemical history of the element. The interval reflects the minimum (a) and the maximum (b) values for the element.

Values given in chevron brackets (e.g., Fm <257>) are the mass numbers of the longest-lived isotope of elements that do not have stable nuclides. However, atomic weights are provided for Th, Pa, and U because these elements have a characteristic abundance in the earth's crust.

For detailed element facts, consult the Periodic Table for individual elements.


Atomic Number - Symbol - Name - Atomic Weight
1  H  - Hydrogen - [1.007 84; 1.008 11]
2  He - Helium - 4.002 602(2)
3  Li - Lithium - [6.938; 6.997]
4  Be - Beryllium - 9.012 1831(5)
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]
9  F  - Fluorine - 18.998 403 163(6)
10 Ne - Neon - 20.1797(6)
11 Na - Sodium - 22.989 769 28(2)
12 Mg - Magnesium - [24.304, 24.307]
13 Al - Aluminium - 26.981 5385(7)
14 Si - Silicon - [28.084; 28.086]
15 P  - Phosphorus - 30.973 761 998(5)
16 S  - Sulfur - [32.059; 32.076]
17 Cl - Chlorine - [35.446; 35.457]
18 Ar - Argon - 39.948(1)
19 K  - Potassium - 39.0983(1)
20 Ca - Calcium - 40.078(4)
21 Sc - Scandium - 44.955 908(5)
22 Ti - Titanium - 47.867(1)
23 V  - Vanadium - 50.9415(1)
24 Cr - Chromium - 51.9961(6)
25 Mn - Manganese - 54.938 044(3)
26 Fe - Iron - 55.845(2)
27 Co - Cobalt - 58.933 194(4)
28 Ni - Nickel 58.6934(4)
29 Cu - Copper - 63.546(3)
30 Zn - Zinc - 65.38(2)
31 Ga - Gallium - 69.723(1)
32 Ge - Germanium - 72.630(8)
33 As - Arsenic - 74.921 595(6)
34 Se - Selenium - 78.971(8)
35 Br - Bromine - [79.901, 79.907]
36 Kr - Krypton - 83.798(2)
37 Rb - Rubidium - 85.4678(3)
38 Sr - Strontium - 87.62(1)
39 Y  - Yttrium - 88.905 84(2)
40 Zr - Zirconium - 91.224(2)
41 Nb - Niobium - 92.906 37(2)
42 Mo - Molybdenum - 95.95(1)
43 Tc - Technetium - <98>
44 Ru - Ruthenium - 101.07(2)
45 Rh - Rhodium - 102.905 50(2)
46 Pd - Palladium - 106.42(1)
47 Ag - Silver - 107.8682(2)
48 Cd - Cadmium - 112.414(4)
49 In - Indium - 114.818(1)
50 Sn - Tin - 118.710(7)
51 Sb - Antimony - 121.760(1)
52 Te - Tellurium - 127.60(3)
53 I  - Iodine - 126.904 47(3)
54 Xe - Xenon - 131.293(6)
55 Cs - Cesium - 132.905 451 96(6)
56 Ba - Barium - 137.327(7)
57 La - Lanthanum - 138.905 47(7)
58 Ce - Cerium - 140.116(1)
59 Pr - Praseodymium - 140.907 66(2)
60 Nd - Neodymium - 144.242(3)
61 Pm - Promethium - <145>
62 Sm - Samarium - 150.36(2)
63 Eu - Europium - 151.964(1)
64 Gd - Gadolinium - 157.25(3)
65 Tb - Terbium - 158.925 35(2)
66 Dy - Dysprosium - 162.500(1)
67 Ho - Holmium - 164.930 33(2)
68 Er - Erbium - 167.259(3)
69 Tm - Thulium - 168.934 22(2)
70 Yb - Ytterbium - 173.054(5)
71 Lu - Lutetium - 174.9668(1)
72 Hf - Hafnium - 178.49(2)
73 Ta - Tantalum - 180.947 88(2)
74 W - Tungsten - 183.84(1)
75 Re - Rhenium - 186.207(1)
76 Os - Osmium - 190.23(3)
77 Ir - Iridium - 192.217(3)
78 Pt - Platinum - 195.084(9)
79 Au - Gold - 196.966 569(5)
80 Hg - Mercury - 200.592(3)
81 Tl - Thallium - [204.382; 204.385]
82 Pb - Lead - 207.2(1)
83 Bi - Bismuth - 208.980 40(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 - 232.037 7(4)
91 Pa - Protactinium - 231.035 88(2)
92 U  - Uranium - 238.028 91(3)
93 Np - Neptunium - <237>
94 Pu - Plutonium - <244>
95 Am - Americium - <243>
96 Cm - Curium - <247>
97 Bk - Berkelium - <247>
98 Cf - Californium - <251>
99 Es - Einsteinium - <252>
100 Fm - Fermium - <257>
101 Md - Mendelevium - <258>
102 No - Nobelium - <259>
103 Lr - Lawrencium - <262>
104 Rf - Rutherfordium - <267>
105 Db - Dubnium - <268>
106 Sg - Seaborgium - <271>
107 Bh - Bohrium - <272>
108 Hs - Hassium - <270>
109 Mt - Meitnerium - <276>
110 Ds - Darmstadtium - <281>
111 Rg - Roentgenium - <280>
112 Cn - Copernicium - <285>
113 Uut - Ununtrium - <284>
114 Fl - Flerovium - <289>
115 Uup - Ununpentium - <288>
116 Lv - Livermorium - <293>
118 Uuo - Ununoctium - <294>

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