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ATOMIC WEIGHTS
Standard Atomic Weights of the Elements, Recommended by the Commission on Atomic Weights and Isotopic Abundances of the International Union of Pure and Applied Chemistry (1997) (©1998 IUPAC)
Standard atomic weights 1997 [In alphabetical order: scaled to Ar(12C)=12, where 12C is a 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 Ar(E) and the uncertainties (in parentheses, following the last significant figure to which they are attributed) apply to elements of natural terrestrial origin. The footnotes to this Table elaborate the types of variation which may occur for individual elements and which may be larger than the listed uncertainties of values of Ar(E). Names of elements with atomic numbers 110, 111 and 112 are temporary.
Name Atomic
Symbol		 Atomic
Number		 Atomic Weight Footnotes
Actinium* Ac 89    
Aluminum Al 13 26.981538(2)  
Americium* Am 95    
Antimony (Stibium) Sb 51 121.760(1) g
Argon Ar 18 39.948(1) g, r
Arsenic As 33 74.92160(2)  
Astatine* At 85    
Barium Ba 56 137.327(7)  
Berkelium* Bk 97    
Beryllium Be 4 9.012182(3)  
Bismuth Bi 83 208.98038(2)  
Bohrium* Bh 107    
Boron B 5 10.811(7) g, m, r
Bromine Br 35 79.904(1)  
Cadmium Cd 48 112.411(8) g
Caesium (Cesium) Cs 55 132.90545(2)  
Calcium Ca 20 40.078(4) g
Californium* Cf 98    
Carbon C 6 12.0107(8) g, r
Cerium Ce 58 140.116(1) g
Chlorine Cl 17 35.4527(9) m
Chromium Cr 24 51.9961(6)  
Cobalt Co 27 58.933200(9)  
Copper Cu 29 63.546(3) r
Curium* Cm 96    
Dubnium* Db 105    
Dysprosium Dy 66 162.50(3) g
Einsteinium* Es 99    
Erbium Er 68 167.26(3) g
Europium Eu 63 151.964(1) g
Fermium* Fm 100    
Fluorine F 9 18.9984032(5)  
Francium* Fr 87    
Gadolinium Gd 64 157.25(3) g
Gallium Ga 31 69.723(1)  
Germanium Ge 32 72.61(2)  
Gold Au 79 196.96655(2)  
Hafnium Hf 72 178.49(2)  
Hassium* Hs 108    
Helium He 2 4.002602(2) g, r
Holmium Ho 67 164.93032(2)  
Hydrogen H 1 1.00794(7) g, m, r
Indium In 49 114.818(3)  
Iodine I 53 126.90447(3)  
Iridium Ir 77 192.217(3)  
Iron Fe 26 55.845(2)  
Krypton Kr 36 83.80(1) g, m
Lanthanum La 57 138.9055(2) g
Lawrencium* Lr 103    
Lead Pb 82 207.2(1) g, r
Lithium Li 3 6.941(2)† g, m, r
Lutetium Lu 71 174.967(1) g
Magnesium Mg 12 24.3050(6)  
Manganese Mn 25 54.938049(9)  
Meitnerium* Mt 109    
Mendelevium* Md 101    
Mercury Hg 80 200.59(2)  
Molybdenum Mo 42 95.94(1) g
Neodymium Nd 60 144.24(3) g
Neon Ne 10 20.1797(6) g, m
Neptunium* Np 93    
Nickel Ni 28 58.6934(2)  
Niobium* Nb 41 92.90638(2)  
Nitrogen N 7 14.00674(7) g, r
Nobelium No 102    
Osmium Os 76 190.23(3) g
Oxygen O 8 15.9994(3) g, r
Palladium Pd 46 106.42(1) g
Phosphorus P 15 30.973762(4)  
Platinum Pt 78 195.078(2)  
Plutonium* Pu 94    
Polonium* Po 84    
Potassium (Kalium) K 19 39.0983(1)  
Praseodymium Pr 59 140.90765(2)  
Promethium* Pm 61    
Protactinium* Pa 91 231.03588(2)  
Radium* Ra 88    
Radon* Rn 86    
Rhenium Re 75 186.207(1)  
Rhodium Rh 45 102.90550(2)  
Rubidium Rb 37 85.4678(3) g
Ruthenium Ru 44 101.07(2) g
Rutherfordium* Rf 104    
Samarium Sm 62 150.36(3) g
Scandium Sc 21 44.955910(8)  
Seaborgium* Sg 106    
Selenium Se 34 78.96(3)  
Silicon Si 14 28.0855(3) r
Silver Ag 47 107.8682(2) g
Sodium (Natrium) Na 11 22.989770(2)  
Strontium Sr 38 87.62(1) g, r
Sulfur S 16 32.066(6) g, r
Tantalum Ta 73 180.9479(1)  
Technetium* Tc 43    
Tellurium Te 52 127.60(3) g
Terbium Tb 65 158.92534(2)  
Thallium Tl 81 204.3833(2)  
Thorium* Th 90 232.0381(1) g
Thulium Tm 69 168.93421(2)  
Tin Sn 50 118.710(7) g
Titanium Ti 22 47.867(1)  
Tungsten (Wolfram) W 74 183.84(1)  
Ununnilium* Uun 110    
Unununium* Uuu 111    
Ununbium* Uub 112    
Uranium* U 92 238.0289(1) g, m
Vanadium V 23 50.9415(1)  
Xenon Xe 54 131.29(2) g, m
Ytterbium Yb 70 173.04(3) g
Yttrium Y 39 88.90585(2)  
Zinc Zn 30 65.39(2)  
Zirconium Zr 40 91.224(2) g
*  Element has no stable nuclides. One or more well-known isotopes are given in the accompanying table with the appropriate relative atomic mass and half-life. However, three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
†  Commercially available Li materials have atomic weights that are known to range between 6.939 and 6.996; if a more accurate value is required, it must be determined for the specific material.
g  geological specimens 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 specimens and that given in the Table may exceed the stated uncertainty.
m  modified isotopic compositions may be found in commercially available material because it 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 Ar(E) being given; the tabulated Ar(E) value should be applicable to any normal material.