It is defined as the average mass of atoms of an element, which is calculated with the help of relative abundance of isotopes of a naturally occurring element. For example, the atomic mass of hydrogen is 1.0079 and carbon is 12.011. Atomic number is defined as the number of protons in an element. Average atomic mass = f 1 M 1 + f 2 M 2 + + f n M n where f is the fraction representing the natural abundance of the isotope and M is the mass number (weight) of the isotope. The average atomic mass of an element can be found on the periodic table, typically under the elemental symbol.

IUPAC Commission on Isotopic Abundances and Atomic Weights.

• List of elements by atomic mass This is a list of chemical elements, sorted by atomic mass (or most stable isotope) and color coded according to type of element. Each element's atomic number, name, element symbol, and group and period numbers on the periodic table are given.
• Atomic Mass of Chemical Elements The atomic mass is the mass of an atom.
• Note that isotopic atomic species of a given element is uniquely identified by the mass number A, also called atomic mass number, which is the number of nucleons (protons and neutrons) in an atomic nucleus.

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

Atomic Mass Of Elements List

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.

Atomic Mass Of Elements Rounded Off

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.

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.]

Table 2. List of Elements in Atomic Number Order.

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

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.
2. 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.
3. 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.
4. 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.
5. 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

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.
2. 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.
3. 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.
4. 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.
5. See table 1 for details of range and original paper for the atomic weight of the element from different sources.

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No.		Atomic weight	Name	Sym.	M.P. (°C)	B.P. (°C)	Density* (g/cm3)	Earth crust (%)*	Discovery (Year)	Group*	Electron configuration	Ionization energy (eV)
1	1.008	Hydrogen	H	-259	-253	0.09	0.14	1776	1	1s1	13.60
2	4.003	Helium	He	-272	-269	0.18	1895	18	1s2	24.59
3	6.941	Lithium	Li	180	1,347	0.53	1817	1	[He] 2s1	5.39
4	9.012	Beryllium	Be	1,278	2,970	1.85	1797	2	[He] 2s2	9.32
5	10.811	Boron	B	2,300	2,550	2.34	1808	13	[He] 2s2 2p1	8.30
6	12.011	Carbon	C	3,500	4,827	2.26	0.09	ancient	14	[He] 2s2 2p2	11.26
7	14.007	Nitrogen	N	-210	-196	1.25	1772	15	[He] 2s2 2p3	14.53
8	15.999	Oxygen	O	-218	-183	1.43	46.71	1774	16	[He] 2s2 2p4	13.62
9	18.998	Fluorine	F	-220	-188	1.70	0.03	1886	17	[He] 2s2 2p5	17.42
10	20.180	Neon	Ne	-249	-246	0.90	1898	18	[He] 2s2 2p6	21.56
11	22.990	Sodium	Na	98	883	0.97	2.75	1807	1	[Ne] 3s1	5.14
12	24.305	Magnesium	Mg	639	1,090	1.74	2.08	1755	2	[Ne] 3s2	7.65
13	26.982	Aluminum	Al	660	2,467	2.70	8.07	1825	13	[Ne] 3s2 3p1	5.99
14	28.086	Silicon	Si	1,410	2,355	2.33	27.69	1824	14	[Ne] 3s2 3p2	8.15
15	30.974	Phosphorus	P	44	280	1.82	0.13	1669	15	[Ne] 3s2 3p3	10.49
16	32.065	Sulfur	S	113	445	2.07	0.05	ancient	16	[Ne] 3s2 3p4	10.36
17	35.453	Chlorine	Cl	-101	-35	3.21	0.05	1774	17	[Ne] 3s2 3p5	12.97
18	39.948	Argon	Ar	-189	-186	1.78	1894	18	[Ne] 3s2 3p6	15.76
19	39.098	Potassium	K	64	774	0.86	2.58	1807	1	[Ar] 4s1	4.34
20	40.078	Calcium	Ca	839	1,484	1.55	3.65	1808	2	[Ar] 4s2	6.11
21	44.956	Scandium	Sc	1,539	2,832	2.99	1879	3	[Ar] 3d1 4s2	6.56
22	47.867	Titanium	Ti	1,660	3,287	4.54	0.62	1791	4	[Ar] 3d2 4s2	6.83
23	50.942	Vanadium	V	1,890	3,380	6.11	1830	5	[Ar] 3d3 4s2	6.75
24	51.996	Chromium	Cr	1,857	2,672	7.19	0.04	1797	6	[Ar] 3d5 4s1	6.77
25	54.938	Manganese	Mn	1,245	1,962	7.43	0.09	1774	7	[Ar] 3d5 4s2	7.43
26	55.845	Iron	Fe	1,535	2,750	7.87	5.05	ancient	8	[Ar] 3d6 4s2	7.90
27	58.933	Cobalt	Co	1,495	2,870	8.90	1735	9	[Ar] 3d7 4s2	7.88
28	58.693	Nickel	Ni	1,453	2,732	8.90	0.02	1751	10	[Ar] 3d8 4s2	7.64
29	63.546	Copper	Cu	1,083	2,567	8.96	ancient	11	[Ar] 3d10 4s1	7.73
30	65.390	Zinc	Zn	420	907	7.13	ancient	12	[Ar] 3d10 4s2	9.39
31	69.723	Gallium	Ga	30	2,403	5.91	1875	13	[Ar] 3d10 4s2 4p1	6.00
32	72.640	Germanium	Ge	937	2,830	5.32	1886	14	[Ar] 3d10 4s2 4p2	7.90
33	74.922	Arsenic	As	81	613	5.72	ancient	15	[Ar] 3d10 4s2 4p3	9.79
34	78.960	Selenium	Se	217	685	4.79	1817	16	[Ar] 3d10 4s2 4p4	9.75
35	79.904	Bromine	Br	-7	59	3.12	1826	17	[Ar] 3d10 4s2 4p5	11.81
36	83.800	Krypton	Kr	-157	-153	3.75	1898	18	[Ar] 3d10 4s2 4p6	14.00
37	85.468	Rubidium	Rb	39	688	1.63	1861	1	[Kr] 5s1	4.18
38	87.620	Strontium	Sr	769	1,384	2.54	1790	2	[Kr] 5s2	5.69
39	88.906	Yttrium	Y	1,523	3,337	4.47	1794	3	[Kr] 4d1 5s2	6.22
40	91.224	Zirconium	Zr	1,852	4,377	6.51	0.03	1789	4	[Kr] 4d2 5s2	6.63
41	92.906	Niobium	Nb	2,468	4,927	8.57	1801	5	[Kr] 4d4 5s1	6.76
42	95.940	Molybdenum	Mo	2,617	4,612	10.22	1781	6	[Kr] 4d5 5s1	7.09
43	*	98.000	Technetium	Tc	2,200	4,877	11.50	1937	7	[Kr] 4d5 5s2	7.28
44	101.070	Ruthenium	Ru	2,250	3,900	12.37	1844	8	[Kr] 4d7 5s1	7.36
45	102.906	Rhodium	Rh	1,966	3,727	12.41	1803	9	[Kr] 4d8 5s1	7.46
46	106.420	Palladium	Pd	1,552	2,927	12.02	1803	10	[Kr] 4d10	8.34
47	107.868	Silver	Ag	962	2,212	10.50	ancient	11	[Kr] 4d10 5s1	7.58
48	112.411	Cadmium	Cd	321	765	8.65	1817	12	[Kr] 4d10 5s2	8.99
49	114.818	Indium	In	157	2,000	7.31	1863	13	[Kr] 4d10 5s2 5p1	5.79
50	118.710	Tin	Sn	232	2,270	7.31	ancient	14	[Kr] 4d10 5s2 5p2	7.34
51	121.760	Antimony	Sb	630	1,750	6.68	ancient	15	[Kr] 4d10 5s2 5p3	8.61
52	127.600	Tellurium	Te	449	990	6.24	1783	16	[Kr] 4d10 5s2 5p4	9.01
53	126.905	Iodine	I	114	184	4.93	1811	17	[Kr] 4d10 5s2 5p5	10.45
54	131.293	Xenon	Xe	-112	-108	5.90	1898	18	[Kr] 4d10 5s2 5p6	12.13
55	132.906	Cesium	Cs	29	678	1.87	1860	1	[Xe] 6s1	3.89
56	137.327	Barium	Ba	725	1,140	3.59	0.05	1808	2	[Xe] 6s2	5.21
57	138.906	Lanthanum	La	920	3,469	6.15	1839	3	[Xe] 5d1 6s2	5.58
58	140.116	Cerium	Ce	795	3,257	6.77	1803	101	[Xe] 4f1 5d1 6s2	5.54
59	140.908	Praseodymium	Pr	935	3,127	6.77	1885	101	[Xe] 4f3 6s2	5.47
60	144.240	Neodymium	Nd	1,010	3,127	7.01	1885	101	[Xe] 4f4 6s2	5.53
61	*	145.000	Promethium	Pm	1,100	3,000	7.30	1945	101	[Xe] 4f5 6s2	5.58
62	150.360	Samarium	Sm	1,072	1,900	7.52	1879	101	[Xe] 4f6 6s2	5.64
63	151.964	Europium	Eu	822	1,597	5.24	1901	101	[Xe] 4f7 6s2	5.67
64	157.250	Gadolinium	Gd	1,311	3,233	7.90	1880	101	[Xe] 4f7 5d1 6s2	6.15
65	158.925	Terbium	Tb	1,360	3,041	8.23	1843	101	[Xe] 4f9 6s2	5.86
66	162.500	Dysprosium	Dy	1,412	2,562	8.55	1886	101	[Xe] 4f10 6s2	5.94
67	164.930	Holmium	Ho	1,470	2,720	8.80	1867	101	[Xe] 4f11 6s2	6.02
68	167.259	Erbium	Er	1,522	2,510	9.07	1842	101	[Xe] 4f12 6s2	6.11
69	168.934	Thulium	Tm	1,545	1,727	9.32	1879	101	[Xe] 4f13 6s2	6.18
70	173.040	Ytterbium	Yb	824	1,466	6.90	1878	101	[Xe] 4f14 6s2	6.25
71	174.967	Lutetium	Lu	1,656	3,315	9.84	1907	101	[Xe] 4f14 5d1 6s2	5.43
72	178.490	Hafnium	Hf	2,150	5,400	13.31	1923	4	[Xe] 4f14 5d2 6s2	6.83
73	180.948	Tantalum	Ta	2,996	5,425	16.65	1802	5	[Xe] 4f14 5d3 6s2	7.55
74	183.840	Tungsten	W	3,410	5,660	19.35	1783	6	[Xe] 4f14 5d4 6s2	7.86
75	186.207	Rhenium	Re	3,180	5,627	21.04	1925	7	[Xe] 4f14 5d5 6s2	7.83
76	190.230	Osmium	Os	3,045	5,027	22.60	1803	8	[Xe] 4f14 5d6 6s2	8.44
77	192.217	Iridium	Ir	2,410	4,527	22.40	1803	9	[Xe] 4f14 5d7 6s2	8.97
78	195.078	Platinum	Pt	1,772	3,827	21.45	1735	10	[Xe] 4f14 5d9 6s1	8.96
79	196.967	Gold	Au	1,064	2,807	19.32	ancient	11	[Xe] 4f14 5d10 6s1	9.23
80	200.590	Mercury	Hg	-39	357	13.55	ancient	12	[Xe] 4f14 5d10 6s2	10.44
81	204.383	Thallium	Tl	303	1,457	11.85	1861	13	[Xe] 4f14 5d10 6s2 6p1	6.11
82	207.200	Lead	Pb	327	1,740	11.35	ancient	14	[Xe] 4f14 5d10 6s2 6p2	7.42
83	208.980	Bismuth	Bi	271	1,560	9.75	ancient	15	[Xe] 4f14 5d10 6s2 6p3	7.29
84	*	209.000	Polonium	Po	254	962	9.30	1898	16	[Xe] 4f14 5d10 6s2 6p4	8.42
85	*	210.000	Astatine	At	302	337	0.00	1940	17	[Xe] 4f14 5d10 6s2 6p5	9.30
86	*	222.000	Radon	Rn	-71	-62	9.73	1900	18	[Xe] 4f14 5d10 6s2 6p6	10.75
87	*	223.000	Francium	Fr	27	677	0.00	1939	1	[Rn] 7s1	4.07
88	*	226.000	Radium	Ra	700	1,737	5.50	1898	2	[Rn] 7s2	5.28
89	*	227.000	Actinium	Ac	1,050	3,200	10.07	1899	3	[Rn] 6d1 7s2	5.17
90	232.038	Thorium	Th	1,750	4,790	11.72	1829	102	[Rn] 6d2 7s2	6.31
91	231.036	Protactinium	Pa	1,568	0	15.40	1913	102	[Rn] 5f2 6d1 7s2	5.89
92	238.029	Uranium	U	1,132	3,818	18.95	1789	102	[Rn] 5f3 6d1 7s2	6.19
93	*	237.000	Neptunium	Np	640	3,902	20.20	1940	102	[Rn] 5f4 6d1 7s2	6.27
94	*	244.000	Plutonium	Pu	640	3,235	19.84	1940	102	[Rn] 5f6 7s2	6.03
95	*	243.000	Americium	Am	994	2,607	13.67	1944	102	[Rn] 5f7 7s2	5.97
96	*	247.000	Curium	Cm	1,340	0	13.50	1944	102	5.99
97	*	247.000	Berkelium	Bk	986	0	14.78	1949	102	6.20
98	*	251.000	Californium	Cf	900	0	15.10	1950	102	6.28
99	*	252.000	Einsteinium	Es	860	0	0.00	1952	102	6.42
100	*	257.000	Fermium	Fm	1,527	0	0.00	1952	102	6.50
101	*	258.000	Mendelevium	Md	0	0	0.00	1955	102	6.58
102	*	259.000	Nobelium	No	827	0	0.00	1958	102	6.65
103	*	262.000	Lawrencium	Lr	1,627	0	0.00	1961	102	4.90
104	*	261.000	Rutherfordium	Rf	0	0	0.00	1964	4	0.00
105	*	262.000	Dubnium	Db	0	0	0.00	1967	5	0.00
106	*	266.000	Seaborgium	Sg	0	0	0.00	1974	6	0.00
107	*	264.000	Bohrium	Bh	0	0	0.00	1981	7	0.00
108	*	277.000	Hassium	Hs	0	0	0.00	1984	8	0.00
109	*	268.000	Meitnerium	Mt	0	0	0.00	1982	9	0.00
No.		Atomic weight	Name	Sym.	M.P. (°C)	B.P. (°C)	Density* (g/cm3)	Earth crust (%)*	Discovery (Year)	Group*	Electron configuration	Ionization energy (eV)

Notes:
• Density of elements with boiling points below 0°C is given in g/l. In a sorted list, these elements are shown before other elements that have boiling points >0°C.
• Earth crust composition average values are from a report by F. W. Clarke and H. S. Washington, 1924. Elemental composition of crustal rocks differ between different localities (see article).
• Group: There are only 18 groups in the periodic table that constitute the columns of the table. Lanthanoids and Actinoids are numbered as 101 and 102 to separate them in sorting by group.
• The elements marked with an asterisk (in the 2nd column) have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Abbreviations and Definitions:

No. - Atomic Number; M.P. - melting point; B.P. - boiling point

Atomic number: The number of protons in an atom. Each element is uniquely defined by its atomic number.

Atomic mass: The mass of an atom is primarily determined by the number of protons and neutrons in its nucleus. Atomic mass is measured in Atomic Mass Units (amu) which are scaled relative to carbon, ¹²C, that is taken as a standard element with an atomic mass of 12. This isotope of carbon has 6 protons and 6 neutrons. Thus, each proton and neutron has a mass of about 1 amu.

Atomic Mass Table

Isotope: Atoms of the same element with the same atomic number, but different number of neutrons. Isotope of an element is defined by the sum of the number of protons and neutrons in its nucleus. Elements have more than one isotope with varying numbers of neutrons. For example, there are two common isotopes of carbon, ¹²C and ¹³C which have 6 and 7 neutrons respectively. The abundances of different isotopes of elements vary in nature depending on the source of materials. For relative abundances of isotopes in nature see reference on Atomic Weights and Isotopic Compositions.

Atomic weight: Atomic weight values represent weighted average of the masses of all naturally occurring isotopes of an element. The values shown here are based on the IUPAC Commission determinations (Pure Appl. Chem. 73:667-683, 2001). The elements marked with an asterisk have no stable nuclides. For these elements the weight value shown represents the mass number of the longest-lived isotope of the element.

Electron configuration: See next page for explanation of electron configuration of atoms.

Ionization energy (IE): The energy required to remove the outermost electron from an atom or a positive ion in its ground level. The table lists only the first IE in eV units. To convert to kJ/mol multiply by 96.4869. Reference: NIST Reference Table on Ground states and ionization energies for the neutral atoms. IE decreases going down a column of the periodic table, and increases from left to right in a row. Thus, alkali metals have the lowest IE in a period and Rare gases have the highest.

Atomic Mass Of Elements Pdf

Atomic Mass Of Elements On The Periodic Table

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Atomic Mass Of Elements Pdf

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