> **PROTOTYPE:** a suggestion, not an official CIAAW or IUPAC page. Official values are at [ciaaw.org](https://ciaaw.org).

# Standard Atomic Weights


Values are generated from the [published RDF](downloads.md). An interval means that the atomic weight of normal materials falls within those bounds. A number in brackets is the uncertainty in the last digits.

| *Z* | Symbol | Element | Standard Atomic Weight | Notes |
| --- | --- | --- | --- | --- |
| 1 | H | [hydrogen](elements/Hydrogen.md) | [1.007 84, 1.008 11] | [m](#note-m) |
| 2 | He | [helium](elements/Helium.md) | 4.002 602(2) | [g](#note-g) [r](#note-r) |
| 3 | Li | [lithium](elements/Lithium.md) | [6.938, 6.997] | [m](#note-m) |
| 4 | Be | [beryllium](elements/Beryllium.md) | 9.012 1831(5) |  |
| 5 | B | [boron](elements/Boron.md) | [10.806, 10.821] | [m](#note-m) |
| 6 | C | [carbon](elements/Carbon.md) | [12.0096, 12.0116] |  |
| 7 | N | [nitrogen](elements/Nitrogen.md) | [14.006 43, 14.007 28] | [m](#note-m) |
| 8 | O | [oxygen](elements/Oxygen.md) | [15.999 03, 15.999 77] | [m](#note-m) |
| 9 | F | [fluorine](elements/Fluorine.md) | 18.998 403 162(5) |  |
| 10 | Ne | [neon](elements/Neon.md) | 20.1797(6) | [g](#note-g) [m](#note-m) |
| 11 | Na | [sodium](elements/Sodium.md) | 22.989 769 28(2) |  |
| 12 | Mg | [magnesium](elements/Magnesium.md) | [24.304, 24.307] |  |
| 13 | Al | [aluminium](elements/Aluminium.md) | 26.981 5384(3) |  |
| 14 | Si | [silicon](elements/Silicon.md) | [28.084, 28.086] |  |
| 15 | P | [phosphorus](elements/Phosphorus.md) | 30.973 761 998(5) |  |
| 16 | S | [sulfur](elements/Sulfur.md) | [32.059, 32.076] |  |
| 17 | Cl | [chlorine](elements/Chlorine.md) | [35.446, 35.457] | [m](#note-m) |
| 18 | Ar | [argon](elements/Argon.md) | [39.792, 39.963] |  |
| 19 | K | [potassium](elements/Potassium.md) | 39.0983(1) |  |
| 20 | Ca | [calcium](elements/Calcium.md) | 40.078(4) | [g](#note-g) |
| 21 | Sc | [scandium](elements/Scandium.md) | 44.955 907(4) |  |
| 22 | Ti | [titanium](elements/Titanium.md) | 47.867(1) |  |
| 23 | V | [vanadium](elements/Vanadium.md) | 50.9415(1) |  |
| 24 | Cr | [chromium](elements/Chromium.md) | 51.9961(6) |  |
| 25 | Mn | [manganese](elements/Manganese.md) | 54.938 043(2) |  |
| 26 | Fe | [iron](elements/Iron.md) | 55.845(2) |  |
| 27 | Co | [cobalt](elements/Cobalt.md) | 58.933 194(3) |  |
| 28 | Ni | [nickel](elements/Nickel.md) | 58.6934(4) | [r](#note-r) |
| 29 | Cu | [copper](elements/Copper.md) | 63.546(3) | [r](#note-r) |
| 30 | Zn | [zinc](elements/Zinc.md) | 65.38(2) | [r](#note-r) |
| 31 | Ga | [gallium](elements/Gallium.md) | 69.723(1) |  |
| 32 | Ge | [germanium](elements/Germanium.md) | 72.630(8) |  |
| 33 | As | [arsenic](elements/Arsenic.md) | 74.921 595(6) |  |
| 34 | Se | [selenium](elements/Selenium.md) | 78.971(8) | [r](#note-r) |
| 35 | Br | [bromine](elements/Bromine.md) | [79.901, 79.907] |  |
| 36 | Kr | [krypton](elements/Krypton.md) | 83.798(2) | [g](#note-g) [m](#note-m) |
| 37 | Rb | [rubidium](elements/Rubidium.md) | 85.4678(3) | [g](#note-g) |
| 38 | Sr | [strontium](elements/Strontium.md) | 87.62(1) | [g](#note-g) [r](#note-r) |
| 39 | Y | [yttrium](elements/Yttrium.md) | 88.905 838(2) |  |
| 40 | Zr | [zirconium](elements/Zirconium.md) | 91.222(3) | [g](#note-g) |
| 41 | Nb | [niobium](elements/Niobium.md) | 92.906 37(1) |  |
| 42 | Mo | [molybdenum](elements/Molybdenum.md) | 95.95(1) | [g](#note-g) |
| 43 | Tc | [technetium](elements/Technetium.md) | — |  |
| 44 | Ru | [ruthenium](elements/Ruthenium.md) | 101.07(2) | [g](#note-g) |
| 45 | Rh | [rhodium](elements/Rhodium.md) | 102.905 49(2) |  |
| 46 | Pd | [palladium](elements/Palladium.md) | 106.42(1) | [g](#note-g) |
| 47 | Ag | [silver](elements/Silver.md) | 107.8682(2) | [g](#note-g) |
| 48 | Cd | [cadmium](elements/Cadmium.md) | 112.414(4) | [g](#note-g) |
| 49 | In | [indium](elements/Indium.md) | 114.818(1) |  |
| 50 | Sn | [tin](elements/Tin.md) | 118.710(7) | [g](#note-g) |
| 51 | Sb | [antimony](elements/Antimony.md) | 121.760(1) | [g](#note-g) |
| 52 | Te | [tellurium](elements/Tellurium.md) | 127.60(3) | [g](#note-g) |
| 53 | I | [iodine](elements/Iodine.md) | 126.904 47(3) |  |
| 54 | Xe | [xenon](elements/Xenon.md) | 131.293(6) | [g](#note-g) [m](#note-m) |
| 55 | Cs | [caesium](elements/Caesium.md) | 132.905 451 96(6) |  |
| 56 | Ba | [barium](elements/Barium.md) | 137.327(7) |  |
| 57 | La | [lanthanum](elements/Lanthanum.md) | 138.905 47(7) | [g](#note-g) |
| 58 | Ce | [cerium](elements/Cerium.md) | 140.116(1) | [g](#note-g) |
| 59 | Pr | [praseodymium](elements/Praseodymium.md) | 140.907 66(1) |  |
| 60 | Nd | [neodymium](elements/Neodymium.md) | 144.242(3) | [g](#note-g) |
| 61 | Pm | [promethium](elements/Promethium.md) | — |  |
| 62 | Sm | [samarium](elements/Samarium.md) | 150.36(2) | [g](#note-g) |
| 63 | Eu | [europium](elements/Europium.md) | 151.964(1) | [g](#note-g) |
| 64 | Gd | [gadolinium](elements/Gadolinium.md) | 157.249(2) | [g](#note-g) |
| 65 | Tb | [terbium](elements/Terbium.md) | 158.925 354(7) |  |
| 66 | Dy | [dysprosium](elements/Dysprosium.md) | 162.500(1) | [g](#note-g) |
| 67 | Ho | [holmium](elements/Holmium.md) | 164.930 329(5) |  |
| 68 | Er | [erbium](elements/Erbium.md) | 167.259(3) | [g](#note-g) |
| 69 | Tm | [thulium](elements/Thulium.md) | 168.934 219(5) |  |
| 70 | Yb | [ytterbium](elements/Ytterbium.md) | 173.045(10) | [g](#note-g) |
| 71 | Lu | [lutetium](elements/Lutetium.md) | 174.966 69(5) | [g](#note-g) |
| 72 | Hf | [hafnium](elements/Hafnium.md) | 178.486(6) | [g](#note-g) |
| 73 | Ta | [tantalum](elements/Tantalum.md) | 180.947 88(2) |  |
| 74 | W | [tungsten](elements/Tungsten.md) | 183.84(1) |  |
| 75 | Re | [rhenium](elements/Rhenium.md) | 186.207(1) |  |
| 76 | Os | [osmium](elements/Osmium.md) | 190.23(3) | [g](#note-g) |
| 77 | Ir | [iridium](elements/Iridium.md) | 192.217(2) |  |
| 78 | Pt | [platinum](elements/Platinum.md) | 195.084(9) |  |
| 79 | Au | [gold](elements/Gold.md) | 196.966 570(4) |  |
| 80 | Hg | [mercury](elements/Mercury.md) | 200.592(3) |  |
| 81 | Tl | [thallium](elements/Thallium.md) | [204.382, 204.385] |  |
| 82 | Pb | [lead](elements/Lead.md) | [206.14, 207.94] |  |
| 83 | Bi | [bismuth](elements/Bismuth.md) | 208.980 40(1) |  |
| 84 | Po | [polonium](elements/Polonium.md) | — |  |
| 85 | At | [astatine](elements/Astatine.md) | — |  |
| 86 | Rn | [radon](elements/Radon.md) | — |  |
| 87 | Fr | [francium](elements/Francium.md) | — |  |
| 88 | Ra | [radium](elements/Radium.md) | — |  |
| 89 | Ac | [actinium](elements/Actinium.md) | — |  |
| 90 | Th | [thorium](elements/Thorium.md) | 232.0377(4) | [g](#note-g) |
| 91 | Pa | [protactinium](elements/Protactinium.md) | 231.035 88(1) |  |
| 92 | U | [uranium](elements/Uranium.md) | 238.028 91(3) | [g](#note-g) [m](#note-m) |
| 93 | Np | [neptunium](elements/Neptunium.md) | — |  |
| 94 | Pu | [plutonium](elements/Plutonium.md) | — |  |
| 95 | Am | [americium](elements/Americium.md) | — |  |
| 96 | Cm | [curium](elements/Curium.md) | — |  |
| 97 | Bk | [berkelium](elements/Berkelium.md) | — |  |
| 98 | Cf | [californium](elements/Californium.md) | — |  |
| 99 | Es | [einsteinium](elements/Einsteinium.md) | — |  |
| 100 | Fm | [fermium](elements/Fermium.md) | — |  |
| 101 | Md | [mendelevium](elements/Mendelevium.md) | — |  |
| 102 | No | [nobelium](elements/Nobelium.md) | — |  |
| 103 | Lr | [lawrencium](elements/Lawrencium.md) | — |  |
| 104 | Rf | [rutherfordium](elements/Rutherfordium.md) | — |  |
| 105 | Db | [dubnium](elements/Dubnium.md) | — |  |
| 106 | Sg | [seaborgium](elements/Seaborgium.md) | — |  |
| 107 | Bh | [bohrium](elements/Bohrium.md) | — |  |
| 108 | Hs | [hassium](elements/Hassium.md) | — |  |
| 109 | Mt | [meitnerium](elements/Meitnerium.md) | — |  |
| 110 | Ds | [darmstadtium](elements/Darmstadtium.md) | — |  |
| 111 | Rg | [roentgenium](elements/Roentgenium.md) | — |  |
| 112 | Cn | [copernicium](elements/Copernicium.md) | — |  |
| 113 | Nh | [nihonium](elements/Nihonium.md) | — |  |
| 114 | Fl | [flerovium](elements/Flerovium.md) | — |  |
| 115 | Mc | [moscovium](elements/Moscovium.md) | — |  |
| 116 | Lv | [livermorium](elements/Livermorium.md) | — |  |
| 117 | Ts | [tennessine](elements/Tennessine.md) | — |  |
| 118 | Og | [oganesson](elements/Oganesson.md) | — |  |

## Notes

<a id="note-g"></a>**g** Geological and biological materials 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 materials and that given in the table may exceed the stated uncertainty.

<a id="note-m"></a>**m** Modified isotopic compositions may be found in commercially available material because the material has been subjected to some undisclosed or inadvertent isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the table can occur.

<a id="note-r"></a>**r** Range in isotopic composition of normal terrestrial material prevents a more precise standard atomic weight being given; the tabulated value and uncertainty should be applicable to normal material.