Chemical elements listed by atomic mass

Compare the chemical elements by atomic weight, with names, symbols and atomic numbers.

The first table lists 84 elements in increasing order of abridged standard atomic weight. The remaining 34 elements have no standard atomic weight and appear in a separate table below. Select an element name to open its properties, uses, health and environmental information.

View the colour periodic table Names A–Z List by atomic number List by symbol

Reading the values: standard atomic weights are unitless. Values and ± uncertainties follow CIAAW’s abridged 2024 table. Molar mass uses g/mol; see the explanation below.

Elements sorted by standard atomic weight

Increasing order uses the displayed central values. Some uncertainty ranges overlap, so the ordering is a convenient lookup convention rather than a universal ordering for every sample.

84 elements in increasing order of abridged standard atomic weight; values have no unit.
Abridged standard atomic weight ± uncertainty	Element	Symbol	Atomic number
1.0080 ± 0.0002	Hydrogen	H	1
4.0026 ± 0.0001	Helium	He	2
6.94 ± 0.06	Lithium	Li	3
9.0122 ± 0.0001	Beryllium	Be	4
10.81 ± 0.02	Boron	B	5
12.011 ± 0.002	Carbon	C	6
14.007 ± 0.001	Nitrogen	N	7
15.999 ± 0.001	Oxygen	O	8
18.998 ± 0.001	Fluorine	F	9
20.180 ± 0.001	Neon	Ne	10
22.990 ± 0.001	Sodium	Na	11
24.305 ± 0.002	Magnesium	Mg	12
26.982 ± 0.001	Aluminum Also aluminium	Al	13
28.085 ± 0.001	Silicon	Si	14
30.974 ± 0.001	Phosphorus	P	15
32.06 ± 0.02	Sulfur Also sulphur	S	16
35.45 ± 0.01	Chlorine	Cl	17
39.098 ± 0.001	Potassium	K	19
39.95 ± 0.16	Argon	Ar	18
40.078 ± 0.004	Calcium	Ca	20
44.956 ± 0.001	Scandium	Sc	21
47.867 ± 0.001	Titanium	Ti	22
50.942 ± 0.001	Vanadium	V	23
51.996 ± 0.001	Chromium	Cr	24
54.938 ± 0.001	Manganese	Mn	25
55.845 ± 0.002	Iron	Fe	26
58.693 ± 0.001	Nickel	Ni	28
58.933 ± 0.001	Cobalt	Co	27
63.546 ± 0.003	Copper	Cu	29
65.38 ± 0.02	Zinc	Zn	30
69.723 ± 0.001	Gallium	Ga	31
72.630 ± 0.008	Germanium	Ge	32
74.922 ± 0.001	Arsenic	As	33
78.971 ± 0.008	Selenium	Se	34
79.904 ± 0.003	Bromine	Br	35
83.798 ± 0.002	Krypton	Kr	36
85.468 ± 0.001	Rubidium	Rb	37
87.62 ± 0.01	Strontium	Sr	38
88.906 ± 0.001	Yttrium	Y	39
91.222 ± 0.003	Zirconium	Zr	40
92.906 ± 0.001	Niobium	Nb	41
95.95 ± 0.01	Molybdenum	Mo	42
101.07 ± 0.02	Ruthenium	Ru	44
102.91 ± 0.01	Rhodium	Rh	45
106.42 ± 0.01	Palladium	Pd	46
107.87 ± 0.01	Silver	Ag	47
112.41 ± 0.01	Cadmium	Cd	48
114.82 ± 0.01	Indium	In	49
118.71 ± 0.01	Tin	Sn	50
121.76 ± 0.01	Antimony	Sb	51
126.90 ± 0.01	Iodine	I	53
127.60 ± 0.03	Tellurium	Te	52
131.29 ± 0.01	Xenon	Xe	54
132.91 ± 0.01	Cesium Also caesium	Cs	55
137.33 ± 0.01	Barium	Ba	56
138.91 ± 0.01	Lanthanum	La	57
140.12 ± 0.01	Cerium	Ce	58
140.91 ± 0.01	Praseodymium	Pr	59
144.24 ± 0.01	Neodymium	Nd	60
150.36 ± 0.02	Samarium	Sm	62
151.96 ± 0.01	Europium	Eu	63
157.25 ± 0.01	Gadolinium	Gd	64
158.93 ± 0.01	Terbium	Tb	65
162.50 ± 0.01	Dysprosium	Dy	66
164.93 ± 0.01	Holmium	Ho	67
167.26 ± 0.01	Erbium	Er	68
168.93 ± 0.01	Thulium	Tm	69
173.05 ± 0.02	Ytterbium	Yb	70
174.97 ± 0.01	Lutetium	Lu	71
178.49 ± 0.01	Hafnium	Hf	72
180.95 ± 0.01	Tantalum	Ta	73
183.84 ± 0.01	Tungsten	W	74
186.21 ± 0.01	Rhenium	Re	75
190.23 ± 0.03	Osmium	Os	76
192.22 ± 0.01	Iridium	Ir	77
195.08 ± 0.02	Platinum	Pt	78
196.97 ± 0.01	Gold	Au	79
200.59 ± 0.01	Mercury	Hg	80
204.38 ± 0.01	Thallium	Tl	81
207.2 ± 1.1	Lead	Pb	82
208.98 ± 0.01	Bismuth	Bi	83
231.04 ± 0.01	Protactinium	Pa	91
232.04 ± 0.01	Thorium	Th	90
238.03 ± 0.01	Uranium	U	92

Uncertainty, natural variation and exceptional samples

Isotope proportions vary between materials. CIAAW provides intervals for some elements in its full table; this page uses its abridged values and uncertainties for convenient lookup. For high-precision work, use the full CIAAW table and the isotopic composition of the material being measured.

CIAAW also flags geological materials outside normal variation, modified commercial isotopic compositions and limitations caused by natural variation. Those element-specific flags are not reproduced here; consult the linked source table before applying the values to a particular material. A standard atomic weight is not an exact isotope mass.

Elements without a standard atomic weight

These 34 elements do not have a characteristic isotopic composition in normal terrestrial materials on which to base a standard atomic weight. They are listed here by atomic number.

Some periodic tables show an isotope’s mass number in square brackets for these elements. That integer counts protons plus neutrons in the specified isotope; it is neither a standard atomic weight nor a precise isotope mass. No such isotope mass numbers are mixed into the first table. Thorium, protactinium and uranium do have standard atomic weights and are included above despite being radioactive.

34 elements with no CIAAW standard atomic weight, listed by atomic number.
Standard atomic weight	Element	Symbol	Atomic number
Not assigned	Technetium	Tc	43
Not assigned	Promethium	Pm	61
Not assigned	Polonium	Po	84
Not assigned	Astatine	At	85
Not assigned	Radon	Rn	86
Not assigned	Francium	Fr	87
Not assigned	Radium	Ra	88
Not assigned	Actinium	Ac	89
Not assigned	Neptunium	Np	93
Not assigned	Plutonium	Pu	94
Not assigned	Americium	Am	95
Not assigned	Curium	Cm	96
Not assigned	Berkelium	Bk	97
Not assigned	Californium	Cf	98
Not assigned	Einsteinium	Es	99
Not assigned	Fermium	Fm	100
Not assigned	Mendelevium	Md	101
Not assigned	Nobelium	No	102
Not assigned	Lawrencium	Lr	103
Not assigned	Rutherfordium	Rf	104
Not assigned	Dubnium	Db	105
Not assigned	Seaborgium	Sg	106
Not assigned	Bohrium	Bh	107
Not assigned	Hassium	Hs	108
Not assigned	Meitnerium	Mt	109
Not assigned	Darmstadtium	Ds	110
Not assigned	Roentgenium	Rg	111
Not assigned	Copernicium	Cn	112
Not assigned	Nihonium	Nh	113
Not assigned	Flerovium	Fl	114
Not assigned	Moscovium	Mc	115
Not assigned	Livermorium	Lv	116
Not assigned	Tennessine	Ts	117
Not assigned	Oganesson	Og	118

What do the numbers mean?

Standard atomic weight is a relative value with no unit. Atomic mass describes the mass of an atom and can be expressed in u or Da. Molar mass is expressed in g/mol. At the precision of this table, an element’s atomic-weight value can be used as the numerical molar mass in g/mol for its atoms; for example, iron is approximately 55.845 g/mol.

The values above are the CIAAW abridged standard atomic weights 2024, including the published uncertainties. They describe normal terrestrial materials, rather than a particular isotope or an isotopically enriched sample. The ± notation gives the published uncertainty.

Atomic mass, atomic weight and molar mass: common questions

Why do atomic weights have decimal values?

An element can contain isotopes with different numbers of neutrons. Atomic weight reflects the isotope masses and their relative abundances in the material. For example, chlorine’s abridged standard atomic weight is 35.45 ± 0.01; it is not a statement that a chlorine nucleus contains 35.45 particles.

Why is this order different from the periodic table?

The periodic table follows atomic number, which counts protons. Atomic weight also depends on neutron numbers and isotope proportions. For example, nickel precedes cobalt in this mass-based list even though cobalt has the lower atomic number. Iodine similarly precedes tellurium.

Which element is the lightest or heaviest?

Hydrogen has the lowest standard atomic weight and uranium has the highest among the 84 elements with assigned standard values. Oganesson has the highest atomic number among the 118 recognised elements. For elements without a standard atomic weight, a mass comparison must specify an isotope; a single unqualified “heaviest atomic weight” ranking is misleading.

How do I calculate a compound’s molar mass?

Add each element’s atomic-weight contribution according to the chemical formula. For sodium chloride, NaCl: 22.990 + 35.45 ≈ 58.44 g/mol. For water, H₂O: 2 × 1.0080 + 15.999 ≈ 18.015 g/mol. Elemental oxygen gas is O₂, so its molar mass is approximately 31.998 g/mol, rather than the value for one mole of oxygen atoms.

For formula calculations, open the molecular weight calculator. Use the values and precision appropriate to your material; independently confirm inputs for isotope-labelled or enriched substances.

Using molar mass in water chemistry

Molar mass connects mass concentration with amount concentration. For example, 40.078 mg/L calcium as Ca corresponds to approximately 1.000 mmol/L Ca. Reporting calcium as Ca differs from reporting hardness as CaCO₃; always check the reporting basis before converting.

Explore the elements and water overview, or browse iron in water and lead in water.

More element properties

Property and discovery lists

Electronegativity · Density · Melting point · Boiling point · van der Waals radius · Year of discovery · Discoverer surname · Elements in Earth’s crust · Elements in human body · Covalent radius · Ionization energy

Sources and data version

Values: CIAAW abridged standard atomic weights 2024, based on the 2021 report with the 2024 revisions. For intervals, higher precision and element-specific notes, use the full CIAAW standard atomic weights table. The abridged table can conceal changes visible only at higher precision.

Terminology: IUPAC atomic mass, relative atomic mass and molar mass. For element names, symbols and isotope mass-number notation, see the IUPAC periodic table.

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