Atomic Mass Of Elements

This is a list of the 118 chemical elements which have been identified as of 2021. A chemical element, often simply called an element, is a species of atoms which all have the same number of protons in their atomic nuclei (i.e., the same atomic number, or Z). The atomic weights data were published by J. Meija et al in Atomic Weights of the Elements 2013, and the isotopic compositions data were published by M. Berglund and M.E. Wieser in Isotopic Compositions of the Elements 2009. The relative atomic masses of the isotopes data were published by M. Atomic Mass of Some ElementsGram atomic mass. Gram atomic mass of an element is defined as that much quantity of the element whose mass expressed in grams is numerically equal to its atomic mass. To find gram atomic mass we keep the numerical value the some as the atomic mass, but simply change the units from u to g. For example, atomic mass of.

Atomic Mass Of Elements
Atomic Mass Of Elements Table
Elements Atomic Number And Mass

IUPAC Commission on Isotopic Abundances and Atomic Weights.

These tables are based on the 2015 table with changes from the 2015 table for the values of aluminium, argon, cobalt, gold, holmium, iridium, manganese, niobium, praseodymium, protactinium, rhodium, terbium, thulium and yttrium. See report 5 June 2018. The revised value of hafnium was reported 11 December 2019

https://www.qmul.ac.uk/sbcs/iupac/AtWt/

World Wide Web version of atomic weight data originally prepared by G. P. Moss, from a file provided by D. R. Lide.

Previous values may be consulted from the 1993 table, the 1995 table, the 1997 table, the 1999 table, the 2001 table, the 2005 table, the 2007 table, the 2009 table, the 2011 table, the 2013 table or the 2015 table.

The standard atomic weights of twelve elements having two or more stable isotopes have variability of atomic-weight values in natural terrestrial materials. These are given in table 1 below. In the other lists the values quoted are those suggested for material where the origin of the sample is unknown. For radioactive elements the isotope with the longest half-life is quoted in parenthesis. The original paper should be consulted for full details of the variation in atomic weight and the half life of the radioisotopes quoted below.

A number in parentheses indicates the uncertainty in the last digit of the atomic weight.

See below for the elements listed in Atomic Number Order or Name order.

Atomic Mass Of Elements

See also a copy of the periodic table with atomic weights to five significant figures.

Table 1. List of Elements with Range of Atomic Weights.

At No	Symbol	Name	Minimum Atomic Wt	Maximum Atomic Wt
1	H	hydrogen	1.007 84	1.008 11
3	Li	lithium	6.938	6.997
5	B	boron	10.806	10.821
6	C	carbon	12.0096	12.0116
7	N	nitrogen	14.006 43	14.007 28
8	O	oxygen	15.999 03	15.999 77
12	Mg	magnesium	24.304	24.307
14	Si	silicon	28.084	28.086
16	S	sulfur	32.059	32.076
17	Cl	chlorine	35.446	35.457
18	Ar	argon	39.792	39.963
35	Br	bromine	79.901	79.907
81	Tl	thallium	204.382	204.385

See original paper for the range of these elements from different sources [Isotope-abundance variations and atomic weights of selected elements: 2016 (IUPAC Technical Report), Pure Appl. Chem. 2016, 88(12), 1203-1224.]

Atomic Mass Of Elements Table

Table 2. List of Elements in Atomic Number Order.

Elements Atomic Number And Mass

At No	Symbol	Name	Atomic Wt	Notes
1	H	Hydrogen	1.008	3, 5
2	He	Helium	4.002 602(2)	1, 2
3	Li	Lithium	6.94	3, 5
4	Be	Beryllium	9.012 1831(5)
5	B	Boron	10.81	3, 5
6	C	Carbon	12.011	5
7	N	Nitrogen	14.007	5
8	O	Oxygen	15.999	5
9	F	Fluorine	18.998 403 163(6)
10	Ne	Neon	20.1797(6)	1, 3
11	Na	Sodium	22.989 769 28(2)
12	Mg	Magnesium	24.305	5
13	Al	Aluminium	26.981 5384(3)
14	Si	Silicon	28.085	5
15	P	Phosphorus	30.973 761 998(5)
16	S	Sulfur	32.06	5
17	Cl	Chlorine	35.45	3, 5
18	Ar	Argon	39.948(1)	1, 2, 5
19	K	Potassium	39.0983(1)
20	Ca	Calcium	40.078(4)
21	Sc	Scandium	44.955 908(5)
22	Ti	Titanium	47.867(1)
23	V	Vanadium	50.9415(1)
24	Cr	Chromium	51.9961(6)
25	Mn	Manganese	54.938 043(2)
26	Fe	Iron	55.845(2)
27	Co	Cobalt	58.933 194(3)
28	Ni	Nickel	58.6934(4)	2
29	Cu	Copper	63.546(3)	2
30	Zn	Zinc	65.38(2)	2
31	Ga	Gallium	69.723(1)
32	Ge	Germanium	72.630(8)
33	As	Arsenic	74.921 595(6)
34	Se	Selenium	78.971(8)
35	Br	Bromine	79.904	5
36	Kr	Krypton	83.798(2)	1, 3
37	Rb	Rubidium	85.4678(3)	1
38	Sr	Strontium	87.62(1)	1, 2
39	Y	Yttrium	88.905 84(1)
40	Zr	Zirconium	91.224(2)	1
41	Nb	Niobium	92.906 37(1)
42	Mo	Molybdenum	95.95(1)	1
43	Tc	Technetium	[97]	4
44	Ru	Ruthenium	101.07(2)	1
45	Rh	Rhodium	102.905 49(2)
46	Pd	Palladium	106.42(1)	1
47	Ag	Silver	107.8682(2)	1
48	Cd	Cadmium	112.414(4)	1
49	In	Indium	114.818(1)
50	Sn	Tin	118.710(7)	1
51	Sb	Antimony	121.760(1)	1
52	Te	Tellurium	127.60(3)	1
53	I	Iodine	126.904 47(3)
54	Xe	Xenon	131.293(6)	1, 3
55	Cs	Caesium	132.905 451 96(6)
56	Ba	Barium	137.327(7)
57	La	Lanthanum	138.905 47(7)	1
58	Ce	Cerium	140.116(1)	1
59	Pr	Praseodymium	140.907 66(1)
60	Nd	Neodymium	144.242(3)	1
61	Pm	Promethium	[145]
62	Sm	Samarium	150.36(2)	1
63	Eu	Europium	151.964(1)	1
64	Gd	Gadolinium	157.25(3)	1
65	Tb	Terbium	158.925 354(8)
66	Dy	Dysprosium	162.500(1)	1
67	Ho	Holmium	164.930 328(7)
68	Er	Erbium	167.259(3)	1
69	Tm	Thulium	168.934 218(6)
70	Yb	Ytterbium	173.045(10)	1
71	Lu	Lutetium	174.9668(1)	1
72	Hf	Hafnium	178.486(6)
73	Ta	Tantalum	180.947 88(2)
74	W	Tungsten	183.84(1)
75	Re	Rhenium	186.207(1)
76	Os	Osmium	190.23(3)	1
77	Ir	Iridium	192.217(2)
78	Pt	Platinum	195.084(9)
79	Au	Gold	196.966 570(4)
80	Hg	Mercury	200.592(3)
81	Tl	Thallium	204.38	5
82	Pb	Lead	207.2(1)	1, 2
83	Bi	Bismuth	208.980 40(1)
84	Po	Polonium	[209]	4
85	At	Astatine	[210]	4
86	Rn	Radon	[222]	4
87	Fr	Francium	[223]	4
88	Ra	Radium	[226]	4
89	Ac	Actinium	[227]	4
90	Th	Thorium	232.0377(4)	1, 4
91	Pa	Protactinium	231.035 88(1)	4
92	U	Uranium	238.028 91(3)	1, 3, 4
93	Np	Neptunium	[237]	4
94	Pu	Plutonium	[244]	4
95	Am	Americium	[243]	4
96	Cm	Curium	[247]	4
97	Bk	Berkelium	[247]	4
98	Cf	Californium	[251]	4
99	Es	Einsteinium	[252]	4
100	Fm	Fermium	[257]	4
101	Md	Mendelevium	[258]	4
102	No	Nobelium	[259]	4
103	Lr	Lawrencium	[262]	4
104	Rf	Rutherfordium	[267]	4
105	Db	Dubnium	[270]	4
106	Sg	Seaborgium	[269]	4
107	Bh	Bohrium	[270]	4
108	Hs	Hassium	[270]	4
109	Mt	Meitnerium	[278]	4
110	Ds	Darmstadtium	[281]	4
111	Rg	Roentgenium	[281]	4
112	Cn	Copernicium	[285]	4
113	Nh	Nihonium	[286]	4
114	Fl	Flerovium	[289]	4
115	Mc	Moscovium	[289]	4
116	Lv	Livermorium	[293]	4
117	Ts	Tennessine	[293]	4
118	Og	Oganesson	[294]	4

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.
Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertant isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
See table 1 for details of range and original paper for the atomic weight of the element from different sources.

Table 3. List of Elements in Name Order.

At No	Symbol	Name	Atomic Wt	Notes
89	Ac	Actinium	[227]	4
13	Al	Aluminium	26.981 5384(3)
95	Am	Americium	[243]	4
51	Sb	Antimony	121.760(1)	1
18	Ar	Argon	39.948(1)	1, 2, 5
33	As	Arsenic	74.921 595(6)
85	At	Astatine	[210]	4
56	Ba	Barium	137.327(7)
97	Bk	Berkelium	[247]	4
4	Be	Beryllium	9.012 1831(5)
83	Bi	Bismuth	208.980 40(1)
107	Bh	Bohrium	[270]	4
5	B	Boron	10.81	3, 5
35	Br	Bromine	79.904	5
48	Cd	Cadmium	112.414(4)	1
55	Cs	Caesium	132.905 451 96(6)
20	Ca	Calcium	40.078(4)	1
98	Cf	Californium	[251]	4
6	C	Carbon	12.011	5
58	Ce	Cerium	140.116(1)	1
17	Cl	Chlorine	35.45	3, 5
24	Cr	Chromium	51.9961(6)
27	Co	Cobalt	58.933 194(3)
112	Cn	Copernicium	[285]	4
29	Cu	Copper	63.546(3)	2
96	Cm	Curium	[247]	4
110	Ds	Darmstadtium	[281]	4
105	Db	Dubnium	[270]	4
66	Dy	Dysprosium	162.500(1)	1
99	Es	Einsteinium	[252]	4
68	Er	Erbium	167.259(3)	1
63	Eu	Europium	151.964(1)	1
100	Fm	Fermium	[257]	4
114	Fl	Flerovium	[289]	4
9	F	Fluorine	18.998 403 163(6)
87	Fr	Francium	[223]	4
64	Gd	Gadolinium	157.25(3)	1
31	Ga	Gallium	69.723(1)
32	Ge	Germanium	72.630(8)
79	Au	Gold	196.966 570(4)
72	Hf	Hafnium	178.486(6)
108	Hs	Hassium	[270]	4
2	He	Helium	4.002 602(2)	1, 2
67	Ho	Holmium	164.930 328(7)
1	H	Hydrogen	1.008	3, 5
49	In	Indium	114.818(1)
53	I	Iodine	126.904 47(3)
77	Ir	Iridium	192.217(2)
26	Fe	Iron	55.845(2)
36	Kr	Krypton	83.798(2)	1, 3
57	La	Lanthanum	138.905 47(7)	1
103	Lr	Lawrencium	[262]	4
82	Pb	Lead	207.2(1)	1, 2
3	Li	Lithium	6.94	3, 5
116	Lv	Livermorium	[293]	4
71	Lu	Lutetium	174.9668(1)	1
12	Mg	Magnesium	24.305	5
25	Mn	Manganese	54.938 043(2)
109	Mt	Meitnerium	[278]	4
101	Md	Mendelevium	[258]	4
80	Hg	Mercury	200.592(3)
42	Mo	Molybdenum	95.95(1)	1
115	Mc	Moscovium	[289]	4
60	Nd	Neodymium	144.242(3)	1
10	Ne	Neon	20.1797(6)	1, 3
93	Np	Neptunium	[237]	4
28	Ni	Nickel	58.6934(4)
113	Nh	Nihonium	[286]	4
41	Nb	Niobium	92.906 37(1)
7	N	Nitrogen	14.007	5
102	No	Nobelium	[259]	4
118	Og	Oganesson	[294]	4
76	Os	Osmium	190.23(3)	1
8	O	Oxygen	15.999	5
46	Pd	Palladium	106.42(1)	1
15	P	Phosphorus	30.973 761 998(5)
78	Pt	Platinum	195.084(9)
94	Pu	Plutonium	[244]	4
84	Po	Polonium	[209]	4
19	K	Potassium	39.0983(1)
59	Pr	Praseodymium	140.907 66(1)
61	Pm	Promethium	[145]	4
91	Pa	Protactinium	231.035 88(1)	4
88	Ra	Radium	[226]	4
86	Rn	Radon	[222]	4
75	Re	Rhenium	186.207(1)
45	Rh	Rhodium	102.905 49(2)
111	Rg	Roentgenium	[281]	4
37	Rb	Rubidium	85.4678(3)	1
44	Ru	Ruthenium	101.07(2)	1
104	Rf	Rutherfordium	[267]	4
62	Sm	Samarium	150.36(2)	1
21	Sc	Scandium	44.955 908(5)
106	Sg	Seaborgium	[269]	4
34	Se	Selenium	78.971(8)
14	Si	Silicon	28.085	5
47	Ag	Silver	107.8682(2)	1
11	Na	Sodium	22.989 769 28(2)
38	Sr	Strontium	87.62(1)	1, 2
16	S	Sulfur	32.06	5
73	Ta	Tantalum	180.947 88(2)
43	Tc	Technetium	[97]	4
52	Te	Tellurium	127.60(3)	1
117	Ts	Tennessine	[293]	4
65	Tb	Terbium	158.925 354(8)
81	Tl	Thallium	204.38	5
90	Th	Thorium	232.0377(4)	1, 4
69	Tm	Thulium	168.934 218(6)
50	Sn	Tin	118.710(7)	1
22	Ti	Titanium	47.867(1)
74	W	Tungsten	183.84(1)
92	U	Uranium	238.028 91(3)	1, 3, 4
23	V	Vanadium	50.9415(1)
54	Xe	Xenon	131.293(6)	1, 3
70	Yb	Ytterbium	173.045(10)	1
39	Y	Yttrium	88.905 84(1)
30	Zn	Zinc	65.38(2)	2
40	Zr	Zirconium	91.224(2)	1

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.
Range in isotopic composition of normal terrestrial material prevents a more precise value being given; the tabulated value should be applicable to any normal material.
Modified isotopic compositions may be found in commercially available material because it has been subject to an undisclosed or inadvertant isotopic fractionation. Substantial deviations in atomic weight of the element from that given in the Table can occur.
Element has no stable nuclides. The value enclosed in brackets, e.g. [209], indicates the mass number of the longest-lived isotope of the element. However three such elements (Th, Pa, and U) do have a characteristic terrestrial isotopic composition, and for these an atomic weight is tabulated.
See table 1 for details of range and original paper for the atomic weight of the element from different sources.

Return to IUPAC Chemical Nomenclature home page

The atomic mass of an element is the average mass of the atoms of an element measured in atomic mass unit (amu, also known as daltons, D). The atomic mass is a weighted average of all of the isotopes of that element, in which the mass of each isotope is multiplied by the abundance of that particular isotope. (Atomic mass is also referred to as atomic weight, but the term 'mass' is more accurate.)

For instance, it can be determined experimentally that neon consists of three isotopes: neon-20 (with 10 protons and 10 neutrons in its nucleus) with a mass of 19.992 amu and an abundance of 90.48%, neon-21 (with 10 protons and 11 neutrons) with a mass of 20.994 amu and an abundance of 0.27%, and neon-22 (with 10 protons and 12 neutrons) with a mass of 21.991 amu and an abundance of 9.25%. The average atomic mass of neon is thus:

0.9048	×	19.992 amu	=	18.09 amu
0.0027	×	20.994 amu	=	0.057 amu
0.0925	×	21.991 amu	=	2.03 amu
20.18 amu

The atomic mass is useful in chemistry when it is paired with the mole concept: the atomic mass of an element, measured in amu, is the same as the mass in grams of one mole of an element. Thus, since the atomic mass of iron is 55.847 amu, one mole of iron atoms would weigh 55.847 grams. The same concept can be extended to ionic compounds and molecules. One formula unit of sodium chloride (NaCl) would weigh 58.44 amu (22.98977 amu for Na + 35.453 amu for Cl), so a mole of sodium chloride would weigh 58.44 grams. One molecule of water (H₂O) would weigh 18.02 amu (2×1.00797 amu for H + 15.9994 amu for O), and a mole of water molecules would weigh 18.02 grams.

The original periodic table of the elements published by Dimitri Mendeleev in 1869 arranged the elements that were known at the time in order of increasing atomic weight, since this was prior to the discovery of the nucleus and the interior structure of the atom. The modern periodic table is arranged in order of increasing atomic number instead.