The Info List - Standard Atomic Weight

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The standard atomic weight (Ar, standard, a relative atomic mass) is the atomic weight (Ar) of a chemical element, as appearing and met in the earthly environment. It reflects the variance of natural isotopes (and so weight differences) of an element. Values are defined by (restricted to) the IUPAC
(CIAAW) definition of natural, stable, terrestridal sources. It is the most common and practical atomic weight used, for example to determine molar mass. The specified definition is to use many representative sources (samples) from the Earth, so that the value can widely be used as 'the' atomic weight for real life substances—for example, in pharmaceuticals and scientific research. Atomic weights are specific to single sources and samples of an element, such as the atomic weight of carbon in a particular bone from a particular archeological site. Standard atomic weight
Standard atomic weight
generalizes such values to the range of atomic weights which a chemist might expect to derive from many random samples from Earth. This range is the cause of the interval notation in some standard atomic weight values. Out of the 118 known chemical elements, 84 are stable and have this Earth-environment based value. Typically, such a value is, for example helium: Ar, standard(He) = 7000400260200000000♠4.002602(2). The "(2)" indicates the uncertainty in the last digit shown, to read 7000400260200000000♠4.002602 ±6994200000000000000♠0.000002. IUPAC
also publishes abridged values, rounded to five significant figures. For helium, Ar, abridged(He) = 7000400260000000000♠4.0026. For twelve elements the samples diverge on this value, because their sample sources have had a different decay history. For example, thallium (Tl) in sedimentary rocks has a different isotopic composition than in igneous rocks and volcanic gases. For these elements, the standard atomic weight is noted as an interval: Ar, standard(Tl) = [204.38, 204.39]. With such an interval, for less demanding situations, IUPAC
also publishes an conventional value. For thallium, Ar, conventional(Tl) = 7002204380000000000♠204.38.


1 Definition

1.1 Terrestrial definition 1.2 Causes of uncertainty on Earth

2 Determination of relative atomic mass 3 Naming controversy 4 Published values

4.1 Abridged atomic weight 4.2 Conventional atomic weight 4.3 A formal short atomic weight

5 List of atomic weights

5.1 In the periodic table

6 See also 7 References 8 External links


Excerpt of an IUPAC
Periodic Table showing the interval notation of the standard atomic weights of boron, carbon, and nitrogen (Chemistry International, IUPAC). Example: the pie chart for boron shows it to be composed of about 20% 10B and 80% 11B. This isotope mix causes the atomic weight of ordinary Earthly boron samples to be expected to fall within the interval 10.806 to 10.821. and this interval is the standard atomic weight. Boron
samples from unusual sources, particularly non-terrestrial sources, might have measured atomic weights that fall outside this range. Atomic weight and relative atomic mass are synonyms.

The standard atomic weight is thus a more special value of the relative atomic mass. It is defined as the "recommended values" of relative atomic masses of sources in the local environment of the Earth's crust and atmosphere as determined by the IUPAC
Commission on Atomic Weights and Isotopic Abundances. (CIAAW)[2] In general, values from different sources are subject to natural variation due to a different radioactive history of sources. Thus, standard atomic weights are an expectation range of atomic weights from a range of samples or sources. By limiting the sources to terrestrial origin only, the CIAAW-determined values have less variance, and are a more precise value for relative atomic masses (atomic weights) actually found and used in worldly materials. The CIAAW-published values are used and sometimes lawfully required in mass calculations. The values have an uncertainty (noted in brackets), or are an expectation interval (see example in illustration immediately above). This uncertainty reflects natural variability in isotopic distribution for an element, rather than uncertainty in measurement (which is much smaller with quality instruments).[3] Although there is an attempt to cover the range of variability on Earth with standard atomic weight figures, there are known cases of mineral samples which contain elements with atomic weights that are outliers from the standard atomic weight range.[4] For synthetic elements the isotope formed depends on the means of synthesis, so the concept of natural isotope abundance has no meaning. Therefore, for synthetic elements the total nucleon count[dubious – discuss] of the most stable isotope (i.e., the isotope with the longest half-life) is listed in brackets, in place of the standard atomic weight.

When the term "atomic weight" is used in chemistry, usually it is the more specific standard atomic weight that is implied. It is standard atomic weights that are used in periodic tables and many standard references in ordinary terrestrial chemistry. Lithium
represents a unique case where the natural abundances of the isotopes have in some cases been found to have been perturbed by human isotopic separation activities to the point of affecting the uncertainty in its standard atomic weight, even in samples obtained from natural sources, such as rivers.[citation needed, dubious] Terrestrial definition[edit] An example of why “conventional terrestrial sources" must be specified in giving standard atomic weight values is the element argon. Between locations in the Solar System, the atomic weight of argon varies as much as 10%, due to extreme variance in isotopic composition. Where the major source of argon is the decay of 40K in rocks, 40Ar will be the dominant isotope. Such locations include the planets Mercury and Mars, and the moon Titan. On Earth the ratios of the three isotopes 36Ar : 38Ar : 40Ar are approximately 5 : 1 : 1600, giving terrestrial argon a standard atomic weight of 39.948(1). This atomic weight is larger than that of the next element potassium, causing confusion in the days when the places of elements in the periodic table was largely determined according to atomic weight. However, such is not the case in the rest of the universe. Argon produced directly by stellar nucleosynthesis, is dominated by the alpha-process nuclide 36Ar. Correspondingly, solar argon contains 84.6% 36Ar (according to solar wind measurements),[5] and the ratio of the three isotopes 36Ar : 38Ar : 40Ar in the atmospheres of the outer planets is 8400 : 1600 : 1.[6] The atomic weight of argon in the Sun and most of the universe, therefore, would be only approximately 36.3.[7] Causes of uncertainty on Earth[edit] Famously, the published atomic weight value comes with an uncertainty. This uncertainty (and related: precision) follows from its definition, the source being "terrestrial and stable". Systematic causes for uncertainty are:

Measurement limits. As always, the physical measurement is never finite. There is always more detail to be found and read. This applies to every single, pure isotope found. For example, today the mass of the main natural fluorine isotope can be measured to the accuracy of eleven decimal places: 7001189984031630000♠18.998403163(6). But a still more precise measurement system could become available, producing more decimals. Imperfect mixtures of isotopes. In the samples taken and measured the mix (relative abundance) of those isotopes may vary. For example copper. While in general its two isotopes make out 69.15% and 30.85% each of all copper found, the natural sample being measured can have had an incomplete 'stirring' and so the percentages are different. The precision is improved by measuring more samples of course, but there remains this cause of uncertainty. (Example: lead samples vary so much, it can not be noted more precise than four figures: 7002207200000000000♠207.2) Earthly sources with a different history. A source is the greater area being researched, for example 'ocean water' or 'volcanic rock' (as opposed to a 'sample': the single heap of material being investigated). It appears that some elements have a different isotopic mix per source. For example, thallium in igneous rock has more lighter isotopes, while in sedimentary rock it has more heavy isotopes. There is no Earthly mean number. These elements show the interval notation: Ar, standard(Tl) = [7002204380000000000♠204.38, 7002204390000000000♠204.39]. For practical reasons, a simplified 'conventional' number is published too (for Tl: 204.38).

These three uncertainties are accumulative. The published value is a result of all these. Determination of relative atomic mass[edit] Main article: Isotope
geochemistry Modern relative atomic masses (a term specific to a given element sample) are calculated from measured values of atomic mass (for each nuclide) and isotopic composition of a sample. Highly accurate atomic masses are available[8][9] for virtually all non-radioactive nuclides, but isotopic compositions are both harder to measure to high precision and more subject to variation between samples.[10][11] For this reason, the relative atomic masses of the 22 mononuclidic elements (which are the same as the isotopic masses for each of the single naturally occurring nuclides of these elements) are known to especially high accuracy. For example, there is an uncertainty of only one part in 38 million for the relative atomic mass of fluorine, a precision which is greater than the current best value for the Avogadro constant
Avogadro constant
(one part in 20 million).

Isotope Atomic mass[9] Abundance[10]

Standard Range

28Si 27.976 926 532 46(194) 92.2297(7)% 92.21–92.25%

29Si 28.976 494 700(22) 4.6832(5)% 4.67–4.69%

30Si 29.973 770 171(32) 3.0872(5)% 3.08–3.10%

The calculation is exemplified for silicon, whose relative atomic mass is especially important in metrology. Silicon
exists in nature as a mixture of three isotopes: 28Si, 29Si and 30Si. The atomic masses of these nuclides are known to a precision of one part in 14 billion for 28Si and about one part in one billion for the others. However the range of natural abundance for the isotopes is such that the standard abundance can only be given to about ±0.001% (see table). The calculation is

Ar(Si) = (27.97693 × 0.922297) + (28.97649 × 0.046832) + (29.97377 × 0.030872) = 28.0854

The estimation of the uncertainty is complicated,[12] especially as the sample distribution is not necessarily symmetrical: the IUPAC standard relative atomic masses are quoted with estimated symmetrical uncertainties,[13] and the value for silicon is 28.0855(3). The relative standard uncertainty in this value is 1×10–5 or 10 ppm. To further reflect this natural variability, in 2010, IUPAC
made the decision to list the relative atomic masses of 10 elements as an interval rather than a fixed number.[14] Naming controversy[edit] The use of the name "atomic weight" has attracted a great deal of controversy among scientists.[15] Objectors to the name usually prefer the term "relative atomic mass" (not to be confused with atomic mass). The basic objection is that atomic weight is not a weight, that is the force exerted on an object in a gravitational field, measured in units of force such as the newton or poundal. In reply, supporters of the term "atomic weight" point out (among other arguments)[15] that

the name has been in continuous use for the same quantity since it was first conceptualized in 1808;[16] for most of that time, atomic weights really were measured by weighing (that is by gravimetric analysis) and the name of a physical quantity should not change simply because the method of its determination has changed; the term "relative atomic mass" should be reserved for the mass of a specific nuclide (or isotope), while "atomic weight" be used for the weighted mean of the atomic masses over all the atoms in the sample; it is not uncommon to have misleading names of physical quantities which are retained for historical reasons, such as

electromotive force, which is not a force resolving power, which is not a power quantity molar concentration, which is not a molar quantity (a quantity expressed per unit amount of substance).

It could be added that atomic weight is often not truly "atomic" either, as it does not correspond to the property of any individual atom. The same argument could be made against "relative atomic mass" used in this sense. Published values[edit] IUPAC
publishes one formal value for each stable element, called the standard atomic weight.[17][18] Any updates are published biannually (in uneven years). The last change was published in 2015, setting a new value for ytterbium[19] In 2017, no changes were published. The value published can have and uncertainty be an interval like for neon: 7001201797000000000♠20.1797(6), or can be an interval, like for boron: [10.806, 10.821]. Next to these 84 values, IUPAC
also publises abridged values (up to five digits per number only), and for the twelve interval values, conventional values (single number values). Symbol Ar is a relative atomic mass, for example from a specific sample. To be specific, the standard atomic weight can be noted as Ar, standard(E), where (E) is the element symbol. Abridged atomic weight[edit] The abridged atomic weight, also published by CIAAW, is derived from the standard atomic weight reducing the numbers to five digits (five significant figures). The name does not say 'rounded'. Interval borders are rounded downwards for the first (lowmost) border, and upwards for the upward (upmost) border. This way, the more precise original interval is fully covered.[20] Examples:

Calcium: Ar, standard(Ca) = 40.078(4) → Ar, abridged(Ca) = 40.078 Helium: Ar, standard(He) = 4.002602(2) → Ar, abridged(He) = 4.0026 Hydrogen: Ar, standard(H) = [1.00784, 1.00811] → Ar, abridged(H) = [1.0078, 1.0082]

Conventional atomic weight[edit] Twelve chemical elements have a standard atomic weight that is defined not as a single number, but as an interval. For example, hydrogen has Ar, standard(H) = [1.00 784, 1.00811]. This notation states that the various sources on Earth have substantially different isotopic constitutions, and uncertainties are incorporated in the two numbers. For these elements, there is not an 'Earth average' constitution, and the 'right' value is not its middle (that would be 1.007975 for hydrogen, with an uncertainty of (±0.000135) that would make it just cover the interval). However, for situations where a less precise value is acceptable, CIAAW
has published a single-number conventional atomic weight that can be used for example in trade. For hydrogen, Ar, conventional(H) = 1.008. The twelve elements are: hydrogen, lithium, boron, carbon, nitrogen, oxygen, magnesium, silicon, sulfur, chlorine, bromine and thallium.[21] A formal short atomic weight[edit] By using the abridged value, and the conventional value for the twelve interval values, a short IUPAC-defined value (5 digits plus uncertainty) can be given for all stable elements. In many situations, and in periodic tables, this may be sufficiently detailed.[22]

Overview: formal values the standard atomic weight[1]

v t e

Element Ar, standard Ar, std abridged[18] Ar, std conventional[20] Ar, std formal short[21] Mass number (most stable isotope)

hydrogen 1H [7000100784000000000♠1.00784, 7000100811000000000♠1.00811] [7000100780000000000♠1.0078, 7000100820000000000♠1.0082] 7000100800000000000♠1.008 7000100800000000000♠1.008

nitrogen 7N [7001140064300000000♠14.00643, 7001140072800000000♠14.00728] [7001140060000000000♠14.006, 7001140079999999999♠14.008] 7001140070000000000♠14.007 7001140070000000000♠14.007

fluorine 9F 7001189984031630000♠18.998403163(6) 7001189980000000000♠18.998


calcium 20Ca 7001400780000000000♠40.078(4) 7001400780000000000♠40.078(4)


technetium 43Tc (none)


List of atomic weights[edit]

v t e

Standard atomic weight
Standard atomic weight
of the elements ( IUPAC
2013,[1] 2015[23])

Z Symbol Name Ar, standard abridged conventional → formal, short note


1 H hydrogen [7000100784000000000♠1.00784, 7000100811000000000♠1.00811] [7000100780000000000♠1.0078, 7000100820000000000♠1.0082] 7000100800000000000♠1.008 7000100800000000000♠1.008

2 He helium 7000400260200000000♠4.002602(2) 7000400260000000000♠4.0026


3 Li lithium [7000693800000000000♠6.938, 7000699700000000000♠6.997] [7000693800000000000♠6.938, 7000699700000000000♠6.997] 7000694000000000000♠6.94 7000694000000000000♠6.94

4 Be beryllium 7000901218310000000♠9.0121831(5) 7000901220000000000♠9.0122


5 B boron [7001108059999999999♠10.806, 7001108210000000000♠10.821] [7001108059999999999♠10.806, 7001108210000000000♠10.821] 7001108100000000000♠10.81 7001108100000000000♠10.81

6 C carbon [7001120096000000000♠12.0096, 7001120116000000000♠12.0116] [7001120090000000000♠12.009, 7001120120000000000♠12.012] 7001120110000000000♠12.011 7001120110000000000♠12.011

7 N nitrogen [7001140064300000000♠14.00643, 7001140072800000000♠14.00728] [7001140060000000000♠14.006, 7001140079999999999♠14.008] 7001140070000000000♠14.007 7001140070000000000♠14.007

8 O oxygen [7001159990300000000♠15.99903, 7001159997700000000♠15.99977] [7001159990000000000♠15.999, 7001160000000000000♠16.000] 7001159990000000000♠15.999 7001159990000000000♠15.999

9 F fluorine 7001189984031630000♠18.998403163(6) 7001189980000000000♠18.998


10 Ne neon 7001201797000000000♠20.1797(6) 7001201800000000000♠20.180


11 Na sodium 7001229897692800000♠22.98976928(2) 7001229899999999999♠22.990


12 Mg magnesium [7001243040000000000♠24.304, 7001243070000000000♠24.307] [7001243040000000000♠24.304, 7001243070000000000♠24.307] 7001243050000000000♠24.305 7001243050000000000♠24.305

13 Al aluminium 7001269815385000000♠26.9815385(7) 7001269820000000000♠26.982


14 Si silicon [7001280840000000000♠28.084, 7001280860000000000♠28.086] [7001280840000000000♠28.084, 7001280860000000000♠28.086] 7001280850000000000♠28.085 7001280850000000000♠28.085

15 P phosphorus 7001309737619980000♠30.973761998(5) 7001309740000000000♠30.974


16 S sulfur [7001320590000000000♠32.059, 7001320760000000000♠32.076] [7001320590000000000♠32.059, 7001320760000000000♠32.076] 7001320600000000000♠32.06 7001320600000000000♠32.06

17 Cl chlorine [7001354460000000000♠35.446, 7001354570000000000♠35.457] [7001354460000000000♠35.446, 7001354570000000000♠35.457] 7001354500000000000♠35.45 7001354500000000000♠35.45

18 Ar argon 7001399480000000000♠39.948(1) 7001399480000000000♠39.948


19 K potassium 7001390983000000000♠39.0983(1) 7001390980000000000♠39.098


20 Ca calcium 7001400780000000000♠40.078(4) 7001400780000000000♠40.078(4)


21 Sc scandium 7001449559080000000♠44.955908(5) 7001449560000000000♠44.956


22 Ti titanium 7001478670000000000♠47.867(1) 7001478670000000000♠47.867


23 V vanadium 7001509415000000000♠50.9415(1) 7001509420000000000♠50.942


24 Cr chromium 7001519961000000000♠51.9961(6) 7001519960000000000♠51.996


25 Mn manganese 7001549380440000000♠54.938044(3) 7001549380000000000♠54.938


26 Fe iron 7001558450000000000♠55.845(2) 7001558450000000000♠55.845(2)


27 Co cobalt 7001589331940000000♠58.933194(4) 7001589330000000000♠58.933


28 Ni nickel 7001586934000000000♠58.6934(4) 7001586930000000000♠58.693


29 Cu copper 7001635460000000000♠63.546(3) 7001635460000000000♠63.546(3)


30 Zn zinc 7001653800000000000♠65.38(2) 7001653800000000000♠65.38(2)


31 Ga gallium 7001697230000000000♠69.723(1) 7001697230000000000♠69.723


32 Ge germanium 7001726300000000000♠72.630(8) 7001726300000000000♠72.630(8)


33 As arsenic 7001749215950000000♠74.921595(6) 7001749220000000000♠74.922


34 Se selenium 7001789710000000000♠78.971(8) 7001789710000000000♠78.971(8)


35 Br bromine [7001799010000000000♠79.901, 7001799070000000000♠79.907] [7001799010000000000♠79.901, 7001799070000000000♠79.907] 7001799040000000000♠79.904 7001799040000000000♠79.904

36 Kr krypton 7001837980000000000♠83.798(2) 7001837980000000000♠83.798(2)


37 Rb rubidium 7001854678000000000♠85.4678(3) 7001854680000000000♠85.468


38 Sr strontium 7001876200000000000♠87.62(1) 7001876200000000000♠87.62


39 Y yttrium 7001889058400000000♠88.90584(2) 7001889060000000000♠88.906


40 Zr zirconium 7001912240000000000♠91.224(2) 7001912240000000000♠91.224(2)


41 Nb niobium 7001929063700000000♠92.90637(2) 7001929060000000000♠92.906


42 Mo molybdenum 7001959500000000000♠95.95(1) 7001959500000000000♠95.95


43 Tc technetium -


44 Ru ruthenium 7002101070000000000♠101.07(2) 7002101070000000000♠101.07(2)


45 Rh rhodium 7002102905500000000♠102.90550(2) 7002102910000000000♠102.91


46 Pd palladium 7002106420000000000♠106.42(1) 7002106420000000000♠106.42


47 Ag silver 7002107868200000000♠107.8682(2) 7002107870000000000♠107.87


48 Cd cadmium 7002112414000000000♠112.414(4) 7002112410000000000♠112.41


49 In indium 7002114818000000000♠114.818(1) 7002114820000000000♠114.82


50 Sn tin 7002118710000000000♠118.710(7) 7002118710000000000♠118.71


51 Sb antimony 7002121760000000000♠121.760(1) 7002121760000000000♠121.76


52 Te tellurium 7002127600000000000♠127.60(3) 7002127600000000000♠127.60(3)


53 I iodine 7002126904470000000♠126.90447(3) 7002126900000000000♠126.90


54 Xe xenon 7002131293000000000♠131.293(6) 7002131289999999999♠131.29


55 Cs caesium 7002132905451960000♠132.90545196(6) 7002132910000000000♠132.91


56 Ba barium 7002137327000000000♠137.327(7) 7002137330000000000♠137.33


57 La lanthanum 7002138905470000000♠138.90547(7) 7002138910000000000♠138.91


58 Ce cerium 7002140116000000000♠140.116(1) 7002140120000000000♠140.12


59 Pr praseodymium 7002140907660000000♠140.90766(2) 7002140910000000000♠140.91


60 Nd neodymium 7002144242000000000♠144.242(3) 7002144240000000000♠144.24


61 Pm promethium -


62 Sm samarium 7002150360000000000♠150.36(2) 7002150360000000000♠150.36(2)


63 Eu europium 7002151964000000000♠151.964(1) 7002151960000000000♠151.96


64 Gd gadolinium 7002157250000000000♠157.25(3) 7002157250000000000♠157.25(3)


65 Tb terbium 7002158925350000000♠158.92535(2) 7002158930000000000♠158.93


66 Dy dysprosium 7002162500000000000♠162.500(1) 7002162500000000000♠162.50


67 Ho holmium 7002164930330000000♠164.93033(2) 7002164930000000000♠164.93


68 Er erbium 7002167259000000000♠167.259(3) 7002167260000000000♠167.26


69 Tm thulium 7002168934220000000♠168.93422(2) 7002168930000000000♠168.93


70 Yb ytterbium 7002173045000000000♠173.045(10) 7002173050000000000♠173.05

7002173050000000000♠173.05 2015[23]

71 Lu lutetium 7002174966800000000♠174.9668(1) 7002174970000000000♠174.97


72 Hf hafnium 7002178490000000000♠178.49(2) 7002178490000000000♠178.49(2)


73 Ta tantalum 7002180947880000000♠180.94788(2) 7002180950000000000♠180.95


74 W tungsten 7002183840000000000♠183.84(1) 7002183840000000000♠183.84


75 Re rhenium 7002186207000000000♠186.207(1) 7002186210000000000♠186.21


76 Os osmium 7002190230000000000♠190.23(3) 7002190230000000000♠190.23(3)


77 Ir iridium 7002192217000000000♠192.217(3) 7002192220000000000♠192.22


78 Pt platinum 7002195084000000000♠195.084(9) 7002195080000000000♠195.08


79 Au gold 7002196966569000000♠196.966569(5) 7002196970000000000♠196.97


80 Hg mercury 7002200592000000000♠200.592(3) 7002200590000000000♠200.59


81 Tl thallium [7002204382000000000♠204.382, 7002204385000000000♠204.385] [7002204380000000000♠204.38, 7002204390000000000♠204.39] 7002204380000000000♠204.38 7002204380000000000♠204.38

82 Pb lead 7002207200000000000♠207.2(1) 7002207200000000000♠207.2


83 Bi bismuth 7002208980400000000♠208.98040(1) 7002208980000000000♠208.98


84 Po polonium -


85 At astatine -


86 Rn radon -


87 Fr francium -


88 Ra radium -


89 Ac actinium -


90 Th thorium 7002232037700000000♠232.0377(4) 7002232040000000000♠232.04


91 Pa protactinium 7002231035880000000♠231.03588(2) 7002231040000000000♠231.04


92 U uranium 7002238028910000000♠238.02891(3) 7002238030000000000♠238.03


93 Np neptunium -


94 Pu plutonium -


95 Am americium -


96 Cm curium -


97 Bk berkelium -


98 Cf californium -


99 Es einsteinium -


100 Fm fermium -


101 Md mendelevium -


102 No nobelium -


103 Lr lawrencium -


104 Rf rutherfordium -


105 Db dubnium -


106 Sg seaborgium -


107 Bh bohrium -


108 Hs hassium -


109 Mt meitnerium -


110 Ds darmstadtium -


111 Rg roentgenium -


112 Cn copernicium -


113 Nh nihonium -


114 Fl flerovium -


115 Mc moscovium -


116 Lv livermorium -


117 Ts tennessine -


118 Og oganesson -


In the periodic table[edit]

v t e

Periodic table

Group 1 2 3   4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Alkali metals Alkaline earth metals

Pnicto­gens Chal­co­gens Halo­gens Noble gases

Period 1



2 Lith­ium3Li7000694000000000000♠6.94 Beryl­lium4Be7000901220000000000♠9.0122

Boron5B7001108100000000000♠10.81 Carbon6C7001120110000000000♠12.011 Nitro­gen7N7001140070000000000♠14.007 Oxy­gen8O7001159990000000000♠15.999 Fluor­ine9F7001189980000000000♠18.998 Neon10Ne7001201800000000000♠20.180

3 So­dium11Na7001229899999999999♠22.990 Magne­sium12Mg7001243050000000000♠24.305

Alumin­ium13Al7001269820000000000♠26.982 Sili­con14Si7001280850000000000♠28.085 Phos­phorus15P7001309740000000000♠30.974 Sulfur16S7001320600000000000♠32.06 Chlor­ine17Cl7001354500000000000♠35.45 Argon18Ar7001399480000000000♠39.948

4 Potas­sium19K7001390980000000000♠39.098 Cal­cium20Ca7001400780000000000♠40.078 Scan­dium21Sc7001449560000000000♠44.956

Tita­nium22Ti7001478670000000000♠47.867 Vana­dium23V7001509420000000000♠50.942 Chrom­ium24Cr7001519960000000000♠51.996 Manga­nese25Mn7001549380000000000♠54.938 Iron26Fe7001558450000000000♠55.845 Cobalt27Co7001589330000000000♠58.933 Nickel28Ni7001586930000000000♠58.693 Copper29Cu7001635460000000000♠63.546 Zinc30Zn7001653800000000000♠65.38 Gallium31Ga7001697230000000000♠69.723 Germa­nium32Ge7001726300000000000♠72.630 Arsenic33As7001749220000000000♠74.922 Sele­nium34Se7001789710000000000♠78.971 Bromine35Br7001799040000000000♠79.904 Kryp­ton36Kr7001837980000000000♠83.798

5 Rubid­ium37Rb7001854680000000000♠85.468 Stront­ium38Sr7001876200000000000♠87.62 Yttrium39Y7001889060000000000♠88.906

Zirco­nium40Zr7001912240000000000♠91.224 Nio­bium41Nb7001929060000000000♠92.906 Molyb­denum42Mo7001959500000000000♠95.95 Tech­netium43Tc[98] Ruthe­nium44Ru7002101070000000000♠101.07 Rho­dium45Rh7002102910000000000♠102.91 Pallad­ium46Pd7002106420000000000♠106.42 Silver47Ag7002107870000000000♠107.87 Cad­mium48Cd7002112410000000000♠112.41 Indium49In7002114820000000000♠114.82 Tin50Sn7002118710000000000♠118.71 Anti­mony51Sb7002121760000000000♠121.76 Tellur­ium52Te7002127600000000000♠127.60 Iodine53I7002126900000000000♠126.90 Xenon54Xe7002131289999999999♠131.29

6 Cae­sium55Cs7002132910000000000♠132.91 Ba­rium56Ba7002137330000000000♠137.33 Lan­thanum57La7002138910000000000♠138.91

Haf­nium72Hf7002178490000000000♠178.49 Tanta­lum73Ta7002180950000000000♠180.95 Tung­sten74W7002183840000000000♠183.84 Rhe­nium75Re7002186210000000000♠186.21 Os­mium76Os7002190230000000000♠190.23 Iridium77Ir7002192220000000000♠192.22 Plat­inum78Pt7002195080000000000♠195.08 Gold79Au7002196970000000000♠196.97 Mer­cury80Hg7002200590000000000♠200.59 Thallium81Tl7002204380000000000♠204.38 Lead82Pb7002207200000000000♠207.2 Bis­muth83Bi7002208980000000000♠208.98 Polo­nium84Po[209] Asta­tine85At[210] Radon86Rn[222]

7 Fran­cium87Fr[223] Ra­dium88Ra[226] Actin­ium89Ac[227]

Ruther­fordium104Rf[267] Dub­nium105Db[268] Sea­borgium106Sg[269] Bohr­ium107Bh[270] Has­sium108Hs[270] Meit­nerium109Mt[278] Darm­stadtium110Ds[281] Roent­genium111Rg[282] Coper­nicium112Cn[285] Nihon­ium113Nh[286] Flerov­ium114Fl[289] Moscov­ium115Mc[290] Liver­morium116Lv[293] Tenness­ine117Ts[294] Oga­nesson118Og[294]

Cerium58Ce7002140120000000000♠140.12 Praseo­dymium59Pr7002140910000000000♠140.91 Neo­dymium60Nd7002144240000000000♠144.24 Prome­thium61Pm[145] Sama­rium62Sm7002150360000000000♠150.36 Europ­ium63Eu7002151960000000000♠151.96 Gadolin­ium64Gd7002157250000000000♠157.25 Ter­bium65Tb7002158930000000000♠158.93 Dyspro­sium66Dy7002162500000000000♠162.50 Hol­mium67Ho7002164930000000000♠164.93 Erbium68Er7002167260000000000♠167.26 Thulium69Tm7002168930000000000♠168.93 Ytter­bium70Yb7002173050000000000♠173.05 Lute­tium71Lu7002174970000000000♠174.97  

Thor­ium90Th7002232040000000000♠232.04 Protac­tinium91Pa7002231040000000000♠231.04 Ura­nium92U7002238030000000000♠238.03 Neptu­nium93Np[237] Pluto­nium94Pu[244] Ameri­cium95Am[243] Curium96Cm[247] Berkel­ium97Bk[247] Califor­nium98Cf[251] Einstei­nium99Es[252] Fer­mium100Fm[257] Mende­levium101Md[258] Nobel­ium102No[259] Lawren­cium103Lr[266]

1 (red)=Gas 3 (black)=Solid 80 (green)=Liquid 109 (gray)=Unknown Color of the atomic number shows state of matter (at 0 °C and 1 atm)

Primordial  From decay  Synthetic Border shows natural occurrence of the element

Standard atomic weight
Standard atomic weight

Ca: 7001400780000000000♠40.078 — Formal short value, rounded (no uncertainty)[24] Po: [209] — mass number of the most stable isotope

Background color shows subcategory in the metal–metalloid–nonmetal trend:

Metal Metalloid Nonmetal Unknown chemical properties

Alkali metal Alkaline earth metal Lan­thanide Actinide Transition metal Post-​transition metal Polyatomic nonmetal Diatomic nonmetal Noble gas

See also[edit]

International Union of Pure and Applied Chemistry
International Union of Pure and Applied Chemistry
(IUPAC) Commission on Isotopic Abundances and Atomic Weights


^ a b c d Meija, J.; et al. (2016). "Atomic weights of the elements 2013 ( IUPAC
Technical Report)". Pure and Applied Chemistry. 88 (3): 265–91. doi:10.1515/pac-2015-0305.  ^ IUPAC
Definition of Standard Atomic Weight ^ Wieser, M. E (2006). "Atomic weights of the elements 2005 (IUPAC Technical Report)" (PDF). Pure and Applied Chemistry. 78 (11): 2051–2066. doi:10.1351/pac200678112051.  ^ IUPAC
Goldbook says Definition of standard atomic weights: "Recommended values of relative atomic masses of the elements revised biennially by the IUPAC
Commission on Atomic Weights and Isotopic Abundances and applicable to elements in any normal sample with a high level of confidence. A normal sample is any reasonably possible source of the element or its compounds in commerce for industry and science and has not been subject to significant modification of isotopic composition within a geologically brief period." ^ Lodders, K. (2008). "The solar argon abundance". Astrophysical Journal. 674: 607–611. arXiv:0710.4523 . Bibcode:2008ApJ...674..607L. doi:10.1086/524725.  ^ Cameron, A. G. W. (1973). "Elemental and isotopic abundances of the volatile elements in the outer planets". Space Science Reviews. 14 (3–4): 392–400. Bibcode:1973SSRv...14..392C. doi:10.1007/BF00214750.  ^ This can be determined from the preceding figures per the definition of atomic weight and WP:CALC ^ National Institute of Standards and Technology. Atomic Weights and Isotopic Compositions for All Elements. ^ a b Wapstra, A.H.; Audi, G.; Thibault, C. (2003), The AME2003 Atomic Mass Evaluation (Online ed.), National Nuclear Data Center . Based on:

Wapstra, A.H.; Audi, G.; Thibault, C. (2003), "The AME2003 atomic mass evaluation (I)", Nuclear Physics A, 729: 129–336, Bibcode:2003NuPhA.729..129W, doi:10.1016/j.nuclphysa.2003.11.002  Audi, G.; Wapstra, A.H.; Thibault, C. (2003), "The AME2003 atomic mass evaluation (II)", Nuclear Physics A, 729: 337–676, Bibcode:2003NuPhA.729..337A, doi:10.1016/j.nuclphysa.2003.11.003 

^ a b Rosman, K. J. R.; Taylor, P. D. P. (1998), "Isotopic Compositions of the Elements 1997" (PDF), Pure and Applied Chemistry, 70 (1): 217–35, doi:10.1351/pac199870010217  ^ Coplen, T. B.; et al. (2002), "Isotopic Abundance Variations of Selected Elements" (PDF), Pure and Applied Chemistry, 74 (10): 1987–2017, doi:10.1351/pac200274101987  ^ Meija, Juris; Mester, Zoltán (2008). "Uncertainty propagation of atomic weight measurement results". Metrologia. 45: 53–62. Bibcode:2008Metro..45...53M. doi:10.1088/0026-1394/45/1/008.  ^ Holden, Norman E. (2004). "Atomic Weights and the International Committee—A Historical Review". Chemistry International. 26 (1): 4–7.  ^ IUPAC
– International Union of Pure and Applied Chemistry: Atomic Weights of Ten Chemical Elements About to Change[dead link] ^ a b de Bièvre, P.; Peiser, H. S. (1992). "'Atomic Weight'—The Name, Its History, Definition, and Units". Pure Appl. Chem. 64 (10): 1535–43. doi:10.1351/pac199264101535.  ^ Dalton, John (1808). A New System of Chemical Philosophy. Manchester.  ^ "Atomic Weights". Retrieved 2018-03-13.  ^ a b IUPAC
2016, Table 1. ^ "Standard Atomic Weights 2015". Commission on Isotopic Abundances and Atomic Weights. 12 October 2015. Retrieved 18 February 2017.  ^ a b IUPAC
2016, Table 2. ^ a b IUPAC
2016, Table 3. ^ IUPAC
2016, Table 2 and Table 3 combined. ^ a b "Standard Atomic Weight
of Ytterbium
Revised". Chemistry International. October 2015. p. 26. doi:10.1515/ci-2015-0512. eISSN 0193-6484. ISSN 0193-6484.  ^ IUPAC
2016, Table 2, 3 combined; uncertainty removed.

External links[edit]

Commission on Isotopic Abundances and Atomic Weights NIST relative atomic masses of all isotopes and the standard atomic weights of the elements Atomic Weights of the Elements 2011

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Chemical elements data


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nomenclature systematic element name

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