IUPAC Periodic Table of the Elements and Isotopes hydrogen helium H He 1 2 1.008 Element has two or more [1.007 84, 1.008 11] Element has no standard 4.002 602(2) Element has two or more isotopes that are used to Element has only one isotope lithium beryllium atomic weight because all of boron carbon nitrogen oxygen fluorine neon isotopes that are used to determine its standard atomic that is used to determine its its isotopes are radioactive determine its atomic weight. weight. The isotopic standard atomic weight. Li Be and, in normal materials, no B C N O F Ne Variations are well known, abundance and atomic Thus, the standard atomic isotope occurs with a 3 4 and the standard atomic weights vary in normal weight is invariant and is 5 6 7 8 9 10 6.94 characteristic isotopic 10.81 12.011 14.007 15.999 weight is given as lower and materials, but upper and given as a single value with [6.938, 6.997] 9.012 1831(5) abundance from which a [10.806, 10.821] [12.0096, 12.0116] [14.006 43, 14.007 28] [15.999 03, 15.999 77] 18.998 403 163(6) 20.1797(6) upper bounds within square lower bounds of the standard an IUPAC evaluated standard atomic weight can sodium magnesium brackets, [ ]. atomic weight have not been uncertainty. aluminium silicon phosphorus sulfur chlorine argon be determined. Na Mg assigned by IUPAC. Al Si P S Cl Ar 11 12 13 14 15 16 17 18 24.305 28.085 32.06 35.45 39.95 22.989 769 28(2) [24.304, 24.307] 26.981 5385(7) [28.084, 28.086] 30.973 761 998(5) [32.059, 32.076] [35.446, 35.457] [39.792, 39.963] potassium calcium scandium titanium vanadium chromium manganese iron cobalt nickel copper zinc gallium germanium arsenic selenium bromine krypton K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 79.904 39.0983(1) 40.078(4) 44.955 908(5) 47.867(1) 50.9415(1) 51.9961(6) 54.938 043(2) 55.845(2) 58.933 194(4) 58.6934(4) 63.546(3) 65.38(2) 69.723(1) 72.630(8) 74.921 595(6) 78.971(8) [79.901, 79.907] 83.798(2) rubidium strontium yttrium zirconium niobium molybdenum technetium ruthenium rhodium palladium silver cadmium indium tin antimony tellurium iodine xenon Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 85.4678(3) 87.62(1) 88.905 84(2) 91.224(2) 92.906 37(2) 95.95(1) 101.07(2) 102.905 49(2) 106.42(1) 107.8682(2) 112.414(4) 114.818(1) 118.710(7) 121.760(1) 127.60(3) 126.904 47(3) 131.293(6) caesium barium hafnium tantalum tungsten rhenium osmium iridium platinum gold mercury thallium lead bismuth polonium astatine radon Cs Ba Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 55 56 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 204.38 132.905 451 96(6) 137.327(7) 178.49(2) 180.947 88(2) 183.84(1) 186.207(1) 190.23(3) 192.217(2) 195.084(9) 196.966 570(4) 200.592(3) [204.382, 204.385] 207.2(1) 208.980 40(1) francium radium rutherfordium dubnium seaborgium bohrium hassium meitnerium darmstadtium roentgenium copernicium nihonium flerovium moscovium livermorium tennessine oganesson Fr Ra Rf Db Sg Bh Hs Mt Ds Rg Cn Nh Fl Mc Lv Ts Og 87 88 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 lanthanum cerium praseodymium neodymium promethium samarium europium gadolinium terbium dysprosium holmium erbium thulium ytterbium lutetium La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb Lu 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 138.905 47(7) 140.116(1) 140.907 66(1) 144.242(3) 150.36(2) 151.964(1) 157.25(3) 158.925 354(8) 162.500(1) 164.930 328(7) 167.259(3) 168.934 218(6) 173.045(10) 174.9668(1) actinium thorium protactinium uranium neptunium plutonium americium curium berkelium californium einsteinium fermium mendelevium nobelium lawrencium Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 232.0377(4) 231.035 88(1) 238.028 91(3) Standard atomic weights are the best estimates by IUPAC of atomic weights that are found in normal materials, which are terrestrial materials that are reasonably possible sources for elements and their compounds in commerce, industry, or science. They are determined using all stable isotopes and selected radioactive isotopes (having relatively long half- lives and characteristic terrestrial isotopic compositions). Isotopes are considered stable (non-radioactive) if evidence for radioactive decay has not been detected experimentally. © IUPAC | This version is dated June 2019. For the interactive version see ISOTOPESMATTER.COM.